1 // SPDX-License-Identifier: GPL-2.0
3 * INET An implementation of the TCP/IP protocol suite for the LINUX
4 * operating system. INET is implemented using the BSD Socket
5 * interface as the means of communication with the user level.
7 * Implementation of the Transmission Control Protocol(TCP).
10 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
11 * Mark Evans, <evansmp@uhura.aston.ac.uk>
12 * Corey Minyard <wf-rch!minyard@relay.EU.net>
13 * Florian La Roche, <flla@stud.uni-sb.de>
14 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
15 * Linus Torvalds, <torvalds@cs.helsinki.fi>
16 * Alan Cox, <gw4pts@gw4pts.ampr.org>
17 * Matthew Dillon, <dillon@apollo.west.oic.com>
18 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
19 * Jorge Cwik, <jorge@laser.satlink.net>
24 * Pedro Roque : Fast Retransmit/Recovery.
26 * Retransmit queue handled by TCP.
27 * Better retransmit timer handling.
28 * New congestion avoidance.
32 * Eric : Fast Retransmit.
33 * Randy Scott : MSS option defines.
34 * Eric Schenk : Fixes to slow start algorithm.
35 * Eric Schenk : Yet another double ACK bug.
36 * Eric Schenk : Delayed ACK bug fixes.
37 * Eric Schenk : Floyd style fast retrans war avoidance.
38 * David S. Miller : Don't allow zero congestion window.
39 * Eric Schenk : Fix retransmitter so that it sends
40 * next packet on ack of previous packet.
41 * Andi Kleen : Moved open_request checking here
42 * and process RSTs for open_requests.
43 * Andi Kleen : Better prune_queue, and other fixes.
44 * Andrey Savochkin: Fix RTT measurements in the presence of
46 * Andrey Savochkin: Check sequence numbers correctly when
47 * removing SACKs due to in sequence incoming
49 * Andi Kleen: Make sure we never ack data there is not
50 * enough room for. Also make this condition
51 * a fatal error if it might still happen.
52 * Andi Kleen: Add tcp_measure_rcv_mss to make
53 * connections with MSS<min(MTU,ann. MSS)
54 * work without delayed acks.
55 * Andi Kleen: Process packets with PSH set in the
57 * J Hadi Salim: ECN support
60 * Panu Kuhlberg: Experimental audit of TCP (re)transmission
61 * engine. Lots of bugs are found.
62 * Pasi Sarolahti: F-RTO for dealing with spurious RTOs
65 #define pr_fmt(fmt) "TCP: " fmt
68 #include <linux/slab.h>
69 #include <linux/module.h>
70 #include <linux/sysctl.h>
71 #include <linux/kernel.h>
72 #include <linux/prefetch.h>
75 #include <net/inet_common.h>
76 #include <linux/ipsec.h>
77 #include <asm/unaligned.h>
78 #include <linux/errqueue.h>
79 #include <trace/events/tcp.h>
80 #include <linux/jump_label_ratelimit.h>
81 #include <net/busy_poll.h>
82 #include <net/mptcp.h>
84 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
86 #define FLAG_DATA 0x01 /* Incoming frame contained data. */
87 #define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */
88 #define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data. */
89 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted. */
90 #define FLAG_SYN_ACKED 0x10 /* This ACK acknowledged SYN. */
91 #define FLAG_DATA_SACKED 0x20 /* New SACK. */
92 #define FLAG_ECE 0x40 /* ECE in this ACK */
93 #define FLAG_LOST_RETRANS 0x80 /* This ACK marks some retransmission lost */
94 #define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/
95 #define FLAG_ORIG_SACK_ACKED 0x200 /* Never retransmitted data are (s)acked */
96 #define FLAG_SND_UNA_ADVANCED 0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
97 #define FLAG_DSACKING_ACK 0x800 /* SACK blocks contained D-SACK info */
98 #define FLAG_SET_XMIT_TIMER 0x1000 /* Set TLP or RTO timer */
99 #define FLAG_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */
100 #define FLAG_UPDATE_TS_RECENT 0x4000 /* tcp_replace_ts_recent() */
101 #define FLAG_NO_CHALLENGE_ACK 0x8000 /* do not call tcp_send_challenge_ack() */
102 #define FLAG_ACK_MAYBE_DELAYED 0x10000 /* Likely a delayed ACK */
103 #define FLAG_DSACK_TLP 0x20000 /* DSACK for tail loss probe */
105 #define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
106 #define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
107 #define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK)
108 #define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED)
110 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
111 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
113 #define REXMIT_NONE 0 /* no loss recovery to do */
114 #define REXMIT_LOST 1 /* retransmit packets marked lost */
115 #define REXMIT_NEW 2 /* FRTO-style transmit of unsent/new packets */
117 #if IS_ENABLED(CONFIG_TLS_DEVICE)
118 static DEFINE_STATIC_KEY_DEFERRED_FALSE(clean_acked_data_enabled, HZ);
120 void clean_acked_data_enable(struct inet_connection_sock *icsk,
121 void (*cad)(struct sock *sk, u32 ack_seq))
123 icsk->icsk_clean_acked = cad;
124 static_branch_deferred_inc(&clean_acked_data_enabled);
126 EXPORT_SYMBOL_GPL(clean_acked_data_enable);
128 void clean_acked_data_disable(struct inet_connection_sock *icsk)
130 static_branch_slow_dec_deferred(&clean_acked_data_enabled);
131 icsk->icsk_clean_acked = NULL;
133 EXPORT_SYMBOL_GPL(clean_acked_data_disable);
135 void clean_acked_data_flush(void)
137 static_key_deferred_flush(&clean_acked_data_enabled);
139 EXPORT_SYMBOL_GPL(clean_acked_data_flush);
142 #ifdef CONFIG_CGROUP_BPF
143 static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb)
145 bool unknown_opt = tcp_sk(sk)->rx_opt.saw_unknown &&
146 BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk),
147 BPF_SOCK_OPS_PARSE_UNKNOWN_HDR_OPT_CB_FLAG);
148 bool parse_all_opt = BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk),
149 BPF_SOCK_OPS_PARSE_ALL_HDR_OPT_CB_FLAG);
150 struct bpf_sock_ops_kern sock_ops;
152 if (likely(!unknown_opt && !parse_all_opt))
155 /* The skb will be handled in the
156 * bpf_skops_established() or
157 * bpf_skops_write_hdr_opt().
159 switch (sk->sk_state) {
166 sock_owned_by_me(sk);
168 memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
169 sock_ops.op = BPF_SOCK_OPS_PARSE_HDR_OPT_CB;
170 sock_ops.is_fullsock = 1;
172 bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
174 BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops);
177 static void bpf_skops_established(struct sock *sk, int bpf_op,
180 struct bpf_sock_ops_kern sock_ops;
182 sock_owned_by_me(sk);
184 memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
185 sock_ops.op = bpf_op;
186 sock_ops.is_fullsock = 1;
188 /* sk with TCP_REPAIR_ON does not have skb in tcp_finish_connect */
190 bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
192 BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops);
195 static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb)
199 static void bpf_skops_established(struct sock *sk, int bpf_op,
205 static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb,
208 static bool __once __read_mostly;
211 struct net_device *dev;
216 dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif);
217 if (!dev || len >= dev->mtu)
218 pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n",
219 dev ? dev->name : "Unknown driver");
224 /* Adapt the MSS value used to make delayed ack decision to the
227 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
229 struct inet_connection_sock *icsk = inet_csk(sk);
230 const unsigned int lss = icsk->icsk_ack.last_seg_size;
233 icsk->icsk_ack.last_seg_size = 0;
235 /* skb->len may jitter because of SACKs, even if peer
236 * sends good full-sized frames.
238 len = skb_shinfo(skb)->gso_size ? : skb->len;
239 if (len >= icsk->icsk_ack.rcv_mss) {
240 icsk->icsk_ack.rcv_mss = min_t(unsigned int, len,
242 /* Account for possibly-removed options */
243 if (unlikely(len > icsk->icsk_ack.rcv_mss +
244 MAX_TCP_OPTION_SPACE))
245 tcp_gro_dev_warn(sk, skb, len);
247 /* Otherwise, we make more careful check taking into account,
248 * that SACKs block is variable.
250 * "len" is invariant segment length, including TCP header.
252 len += skb->data - skb_transport_header(skb);
253 if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
254 /* If PSH is not set, packet should be
255 * full sized, provided peer TCP is not badly broken.
256 * This observation (if it is correct 8)) allows
257 * to handle super-low mtu links fairly.
259 (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
260 !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
261 /* Subtract also invariant (if peer is RFC compliant),
262 * tcp header plus fixed timestamp option length.
263 * Resulting "len" is MSS free of SACK jitter.
265 len -= tcp_sk(sk)->tcp_header_len;
266 icsk->icsk_ack.last_seg_size = len;
268 icsk->icsk_ack.rcv_mss = len;
272 if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
273 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
274 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
278 static void tcp_incr_quickack(struct sock *sk, unsigned int max_quickacks)
280 struct inet_connection_sock *icsk = inet_csk(sk);
281 unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
285 quickacks = min(quickacks, max_quickacks);
286 if (quickacks > icsk->icsk_ack.quick)
287 icsk->icsk_ack.quick = quickacks;
290 void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks)
292 struct inet_connection_sock *icsk = inet_csk(sk);
294 tcp_incr_quickack(sk, max_quickacks);
295 inet_csk_exit_pingpong_mode(sk);
296 icsk->icsk_ack.ato = TCP_ATO_MIN;
298 EXPORT_SYMBOL(tcp_enter_quickack_mode);
300 /* Send ACKs quickly, if "quick" count is not exhausted
301 * and the session is not interactive.
304 static bool tcp_in_quickack_mode(struct sock *sk)
306 const struct inet_connection_sock *icsk = inet_csk(sk);
307 const struct dst_entry *dst = __sk_dst_get(sk);
309 return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
310 (icsk->icsk_ack.quick && !inet_csk_in_pingpong_mode(sk));
313 static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
315 if (tp->ecn_flags & TCP_ECN_OK)
316 tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
319 static void tcp_ecn_accept_cwr(struct sock *sk, const struct sk_buff *skb)
321 if (tcp_hdr(skb)->cwr) {
322 tcp_sk(sk)->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
324 /* If the sender is telling us it has entered CWR, then its
325 * cwnd may be very low (even just 1 packet), so we should ACK
328 if (TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq)
329 inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
333 static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
335 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
338 static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
340 struct tcp_sock *tp = tcp_sk(sk);
342 switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
343 case INET_ECN_NOT_ECT:
344 /* Funny extension: if ECT is not set on a segment,
345 * and we already seen ECT on a previous segment,
346 * it is probably a retransmit.
348 if (tp->ecn_flags & TCP_ECN_SEEN)
349 tcp_enter_quickack_mode(sk, 2);
352 if (tcp_ca_needs_ecn(sk))
353 tcp_ca_event(sk, CA_EVENT_ECN_IS_CE);
355 if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
356 /* Better not delay acks, sender can have a very low cwnd */
357 tcp_enter_quickack_mode(sk, 2);
358 tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
360 tp->ecn_flags |= TCP_ECN_SEEN;
363 if (tcp_ca_needs_ecn(sk))
364 tcp_ca_event(sk, CA_EVENT_ECN_NO_CE);
365 tp->ecn_flags |= TCP_ECN_SEEN;
370 static void tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
372 if (tcp_sk(sk)->ecn_flags & TCP_ECN_OK)
373 __tcp_ecn_check_ce(sk, skb);
376 static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
378 if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
379 tp->ecn_flags &= ~TCP_ECN_OK;
382 static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
384 if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
385 tp->ecn_flags &= ~TCP_ECN_OK;
388 static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
390 if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
395 /* Buffer size and advertised window tuning.
397 * 1. Tuning sk->sk_sndbuf, when connection enters established state.
400 static void tcp_sndbuf_expand(struct sock *sk)
402 const struct tcp_sock *tp = tcp_sk(sk);
403 const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
407 /* Worst case is non GSO/TSO : each frame consumes one skb
408 * and skb->head is kmalloced using power of two area of memory
410 per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
412 SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
414 per_mss = roundup_pow_of_two(per_mss) +
415 SKB_DATA_ALIGN(sizeof(struct sk_buff));
417 nr_segs = max_t(u32, TCP_INIT_CWND, tcp_snd_cwnd(tp));
418 nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
420 /* Fast Recovery (RFC 5681 3.2) :
421 * Cubic needs 1.7 factor, rounded to 2 to include
422 * extra cushion (application might react slowly to EPOLLOUT)
424 sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2;
425 sndmem *= nr_segs * per_mss;
427 if (sk->sk_sndbuf < sndmem)
428 WRITE_ONCE(sk->sk_sndbuf,
429 min(sndmem, sock_net(sk)->ipv4.sysctl_tcp_wmem[2]));
432 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
434 * All tcp_full_space() is split to two parts: "network" buffer, allocated
435 * forward and advertised in receiver window (tp->rcv_wnd) and
436 * "application buffer", required to isolate scheduling/application
437 * latencies from network.
438 * window_clamp is maximal advertised window. It can be less than
439 * tcp_full_space(), in this case tcp_full_space() - window_clamp
440 * is reserved for "application" buffer. The less window_clamp is
441 * the smoother our behaviour from viewpoint of network, but the lower
442 * throughput and the higher sensitivity of the connection to losses. 8)
444 * rcv_ssthresh is more strict window_clamp used at "slow start"
445 * phase to predict further behaviour of this connection.
446 * It is used for two goals:
447 * - to enforce header prediction at sender, even when application
448 * requires some significant "application buffer". It is check #1.
449 * - to prevent pruning of receive queue because of misprediction
450 * of receiver window. Check #2.
452 * The scheme does not work when sender sends good segments opening
453 * window and then starts to feed us spaghetti. But it should work
454 * in common situations. Otherwise, we have to rely on queue collapsing.
457 /* Slow part of check#2. */
458 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb,
459 unsigned int skbtruesize)
461 struct tcp_sock *tp = tcp_sk(sk);
463 int truesize = tcp_win_from_space(sk, skbtruesize) >> 1;
464 int window = tcp_win_from_space(sk, sock_net(sk)->ipv4.sysctl_tcp_rmem[2]) >> 1;
466 while (tp->rcv_ssthresh <= window) {
467 if (truesize <= skb->len)
468 return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
476 /* Even if skb appears to have a bad len/truesize ratio, TCP coalescing
477 * can play nice with us, as sk_buff and skb->head might be either
478 * freed or shared with up to MAX_SKB_FRAGS segments.
479 * Only give a boost to drivers using page frag(s) to hold the frame(s),
480 * and if no payload was pulled in skb->head before reaching us.
482 static u32 truesize_adjust(bool adjust, const struct sk_buff *skb)
484 u32 truesize = skb->truesize;
486 if (adjust && !skb_headlen(skb)) {
487 truesize -= SKB_TRUESIZE(skb_end_offset(skb));
488 /* paranoid check, some drivers might be buggy */
489 if (unlikely((int)truesize < (int)skb->len))
490 truesize = skb->truesize;
495 static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb,
498 struct tcp_sock *tp = tcp_sk(sk);
501 room = min_t(int, tp->window_clamp, tcp_space(sk)) - tp->rcv_ssthresh;
507 if (!tcp_under_memory_pressure(sk)) {
508 unsigned int truesize = truesize_adjust(adjust, skb);
511 /* Check #2. Increase window, if skb with such overhead
512 * will fit to rcvbuf in future.
514 if (tcp_win_from_space(sk, truesize) <= skb->len)
515 incr = 2 * tp->advmss;
517 incr = __tcp_grow_window(sk, skb, truesize);
520 incr = max_t(int, incr, 2 * skb->len);
521 tp->rcv_ssthresh += min(room, incr);
522 inet_csk(sk)->icsk_ack.quick |= 1;
526 * Adjust rcv_ssthresh according to reserved mem
528 tcp_adjust_rcv_ssthresh(sk);
532 /* 3. Try to fixup all. It is made immediately after connection enters
535 static void tcp_init_buffer_space(struct sock *sk)
537 int tcp_app_win = sock_net(sk)->ipv4.sysctl_tcp_app_win;
538 struct tcp_sock *tp = tcp_sk(sk);
541 if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
542 tcp_sndbuf_expand(sk);
544 tcp_mstamp_refresh(tp);
545 tp->rcvq_space.time = tp->tcp_mstamp;
546 tp->rcvq_space.seq = tp->copied_seq;
548 maxwin = tcp_full_space(sk);
550 if (tp->window_clamp >= maxwin) {
551 tp->window_clamp = maxwin;
553 if (tcp_app_win && maxwin > 4 * tp->advmss)
554 tp->window_clamp = max(maxwin -
555 (maxwin >> tcp_app_win),
559 /* Force reservation of one segment. */
561 tp->window_clamp > 2 * tp->advmss &&
562 tp->window_clamp + tp->advmss > maxwin)
563 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
565 tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
566 tp->snd_cwnd_stamp = tcp_jiffies32;
567 tp->rcvq_space.space = min3(tp->rcv_ssthresh, tp->rcv_wnd,
568 (u32)TCP_INIT_CWND * tp->advmss);
571 /* 4. Recalculate window clamp after socket hit its memory bounds. */
572 static void tcp_clamp_window(struct sock *sk)
574 struct tcp_sock *tp = tcp_sk(sk);
575 struct inet_connection_sock *icsk = inet_csk(sk);
576 struct net *net = sock_net(sk);
578 icsk->icsk_ack.quick = 0;
580 if (sk->sk_rcvbuf < net->ipv4.sysctl_tcp_rmem[2] &&
581 !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
582 !tcp_under_memory_pressure(sk) &&
583 sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
584 WRITE_ONCE(sk->sk_rcvbuf,
585 min(atomic_read(&sk->sk_rmem_alloc),
586 net->ipv4.sysctl_tcp_rmem[2]));
588 if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
589 tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
592 /* Initialize RCV_MSS value.
593 * RCV_MSS is an our guess about MSS used by the peer.
594 * We haven't any direct information about the MSS.
595 * It's better to underestimate the RCV_MSS rather than overestimate.
596 * Overestimations make us ACKing less frequently than needed.
597 * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
599 void tcp_initialize_rcv_mss(struct sock *sk)
601 const struct tcp_sock *tp = tcp_sk(sk);
602 unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
604 hint = min(hint, tp->rcv_wnd / 2);
605 hint = min(hint, TCP_MSS_DEFAULT);
606 hint = max(hint, TCP_MIN_MSS);
608 inet_csk(sk)->icsk_ack.rcv_mss = hint;
610 EXPORT_SYMBOL(tcp_initialize_rcv_mss);
612 /* Receiver "autotuning" code.
614 * The algorithm for RTT estimation w/o timestamps is based on
615 * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
616 * <https://public.lanl.gov/radiant/pubs.html#DRS>
618 * More detail on this code can be found at
619 * <http://staff.psc.edu/jheffner/>,
620 * though this reference is out of date. A new paper
623 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
625 u32 new_sample = tp->rcv_rtt_est.rtt_us;
628 if (new_sample != 0) {
629 /* If we sample in larger samples in the non-timestamp
630 * case, we could grossly overestimate the RTT especially
631 * with chatty applications or bulk transfer apps which
632 * are stalled on filesystem I/O.
634 * Also, since we are only going for a minimum in the
635 * non-timestamp case, we do not smooth things out
636 * else with timestamps disabled convergence takes too
640 m -= (new_sample >> 3);
648 /* No previous measure. */
652 tp->rcv_rtt_est.rtt_us = new_sample;
655 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
659 if (tp->rcv_rtt_est.time == 0)
661 if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
663 delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time);
666 tcp_rcv_rtt_update(tp, delta_us, 1);
669 tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
670 tp->rcv_rtt_est.time = tp->tcp_mstamp;
673 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
674 const struct sk_buff *skb)
676 struct tcp_sock *tp = tcp_sk(sk);
678 if (tp->rx_opt.rcv_tsecr == tp->rcv_rtt_last_tsecr)
680 tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
682 if (TCP_SKB_CB(skb)->end_seq -
683 TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss) {
684 u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
687 if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
690 delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
691 tcp_rcv_rtt_update(tp, delta_us, 0);
697 * This function should be called every time data is copied to user space.
698 * It calculates the appropriate TCP receive buffer space.
700 void tcp_rcv_space_adjust(struct sock *sk)
702 struct tcp_sock *tp = tcp_sk(sk);
706 trace_tcp_rcv_space_adjust(sk);
708 tcp_mstamp_refresh(tp);
709 time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time);
710 if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0)
713 /* Number of bytes copied to user in last RTT */
714 copied = tp->copied_seq - tp->rcvq_space.seq;
715 if (copied <= tp->rcvq_space.space)
719 * copied = bytes received in previous RTT, our base window
720 * To cope with packet losses, we need a 2x factor
721 * To cope with slow start, and sender growing its cwin by 100 %
722 * every RTT, we need a 4x factor, because the ACK we are sending
723 * now is for the next RTT, not the current one :
724 * <prev RTT . ><current RTT .. ><next RTT .... >
727 if (sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf &&
728 !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
732 /* minimal window to cope with packet losses, assuming
733 * steady state. Add some cushion because of small variations.
735 rcvwin = ((u64)copied << 1) + 16 * tp->advmss;
737 /* Accommodate for sender rate increase (eg. slow start) */
738 grow = rcvwin * (copied - tp->rcvq_space.space);
739 do_div(grow, tp->rcvq_space.space);
740 rcvwin += (grow << 1);
742 rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
743 while (tcp_win_from_space(sk, rcvmem) < tp->advmss)
746 do_div(rcvwin, tp->advmss);
747 rcvbuf = min_t(u64, rcvwin * rcvmem,
748 sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);
749 if (rcvbuf > sk->sk_rcvbuf) {
750 WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
752 /* Make the window clamp follow along. */
753 tp->window_clamp = tcp_win_from_space(sk, rcvbuf);
756 tp->rcvq_space.space = copied;
759 tp->rcvq_space.seq = tp->copied_seq;
760 tp->rcvq_space.time = tp->tcp_mstamp;
763 /* There is something which you must keep in mind when you analyze the
764 * behavior of the tp->ato delayed ack timeout interval. When a
765 * connection starts up, we want to ack as quickly as possible. The
766 * problem is that "good" TCP's do slow start at the beginning of data
767 * transmission. The means that until we send the first few ACK's the
768 * sender will sit on his end and only queue most of his data, because
769 * he can only send snd_cwnd unacked packets at any given time. For
770 * each ACK we send, he increments snd_cwnd and transmits more of his
773 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
775 struct tcp_sock *tp = tcp_sk(sk);
776 struct inet_connection_sock *icsk = inet_csk(sk);
779 inet_csk_schedule_ack(sk);
781 tcp_measure_rcv_mss(sk, skb);
783 tcp_rcv_rtt_measure(tp);
787 if (!icsk->icsk_ack.ato) {
788 /* The _first_ data packet received, initialize
789 * delayed ACK engine.
791 tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
792 icsk->icsk_ack.ato = TCP_ATO_MIN;
794 int m = now - icsk->icsk_ack.lrcvtime;
796 if (m <= TCP_ATO_MIN / 2) {
797 /* The fastest case is the first. */
798 icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
799 } else if (m < icsk->icsk_ack.ato) {
800 icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
801 if (icsk->icsk_ack.ato > icsk->icsk_rto)
802 icsk->icsk_ack.ato = icsk->icsk_rto;
803 } else if (m > icsk->icsk_rto) {
804 /* Too long gap. Apparently sender failed to
805 * restart window, so that we send ACKs quickly.
807 tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
811 icsk->icsk_ack.lrcvtime = now;
813 tcp_ecn_check_ce(sk, skb);
816 tcp_grow_window(sk, skb, true);
819 /* Called to compute a smoothed rtt estimate. The data fed to this
820 * routine either comes from timestamps, or from segments that were
821 * known _not_ to have been retransmitted [see Karn/Partridge
822 * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
823 * piece by Van Jacobson.
824 * NOTE: the next three routines used to be one big routine.
825 * To save cycles in the RFC 1323 implementation it was better to break
826 * it up into three procedures. -- erics
828 static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
830 struct tcp_sock *tp = tcp_sk(sk);
831 long m = mrtt_us; /* RTT */
832 u32 srtt = tp->srtt_us;
834 /* The following amusing code comes from Jacobson's
835 * article in SIGCOMM '88. Note that rtt and mdev
836 * are scaled versions of rtt and mean deviation.
837 * This is designed to be as fast as possible
838 * m stands for "measurement".
840 * On a 1990 paper the rto value is changed to:
841 * RTO = rtt + 4 * mdev
843 * Funny. This algorithm seems to be very broken.
844 * These formulae increase RTO, when it should be decreased, increase
845 * too slowly, when it should be increased quickly, decrease too quickly
846 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
847 * does not matter how to _calculate_ it. Seems, it was trap
848 * that VJ failed to avoid. 8)
851 m -= (srtt >> 3); /* m is now error in rtt est */
852 srtt += m; /* rtt = 7/8 rtt + 1/8 new */
854 m = -m; /* m is now abs(error) */
855 m -= (tp->mdev_us >> 2); /* similar update on mdev */
856 /* This is similar to one of Eifel findings.
857 * Eifel blocks mdev updates when rtt decreases.
858 * This solution is a bit different: we use finer gain
859 * for mdev in this case (alpha*beta).
860 * Like Eifel it also prevents growth of rto,
861 * but also it limits too fast rto decreases,
862 * happening in pure Eifel.
867 m -= (tp->mdev_us >> 2); /* similar update on mdev */
869 tp->mdev_us += m; /* mdev = 3/4 mdev + 1/4 new */
870 if (tp->mdev_us > tp->mdev_max_us) {
871 tp->mdev_max_us = tp->mdev_us;
872 if (tp->mdev_max_us > tp->rttvar_us)
873 tp->rttvar_us = tp->mdev_max_us;
875 if (after(tp->snd_una, tp->rtt_seq)) {
876 if (tp->mdev_max_us < tp->rttvar_us)
877 tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
878 tp->rtt_seq = tp->snd_nxt;
879 tp->mdev_max_us = tcp_rto_min_us(sk);
884 /* no previous measure. */
885 srtt = m << 3; /* take the measured time to be rtt */
886 tp->mdev_us = m << 1; /* make sure rto = 3*rtt */
887 tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
888 tp->mdev_max_us = tp->rttvar_us;
889 tp->rtt_seq = tp->snd_nxt;
893 tp->srtt_us = max(1U, srtt);
896 static void tcp_update_pacing_rate(struct sock *sk)
898 const struct tcp_sock *tp = tcp_sk(sk);
901 /* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
902 rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
904 /* current rate is (cwnd * mss) / srtt
905 * In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
906 * In Congestion Avoidance phase, set it to 120 % the current rate.
908 * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
909 * If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
910 * end of slow start and should slow down.
912 if (tcp_snd_cwnd(tp) < tp->snd_ssthresh / 2)
913 rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ss_ratio;
915 rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ca_ratio;
917 rate *= max(tcp_snd_cwnd(tp), tp->packets_out);
919 if (likely(tp->srtt_us))
920 do_div(rate, tp->srtt_us);
922 /* WRITE_ONCE() is needed because sch_fq fetches sk_pacing_rate
923 * without any lock. We want to make sure compiler wont store
924 * intermediate values in this location.
926 WRITE_ONCE(sk->sk_pacing_rate, min_t(u64, rate,
927 sk->sk_max_pacing_rate));
930 /* Calculate rto without backoff. This is the second half of Van Jacobson's
931 * routine referred to above.
933 static void tcp_set_rto(struct sock *sk)
935 const struct tcp_sock *tp = tcp_sk(sk);
936 /* Old crap is replaced with new one. 8)
939 * 1. If rtt variance happened to be less 50msec, it is hallucination.
940 * It cannot be less due to utterly erratic ACK generation made
941 * at least by solaris and freebsd. "Erratic ACKs" has _nothing_
942 * to do with delayed acks, because at cwnd>2 true delack timeout
943 * is invisible. Actually, Linux-2.4 also generates erratic
944 * ACKs in some circumstances.
946 inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
948 /* 2. Fixups made earlier cannot be right.
949 * If we do not estimate RTO correctly without them,
950 * all the algo is pure shit and should be replaced
951 * with correct one. It is exactly, which we pretend to do.
954 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
955 * guarantees that rto is higher.
960 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
962 __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
965 cwnd = TCP_INIT_CWND;
966 return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
969 struct tcp_sacktag_state {
970 /* Timestamps for earliest and latest never-retransmitted segment
971 * that was SACKed. RTO needs the earliest RTT to stay conservative,
972 * but congestion control should still get an accurate delay signal.
979 unsigned int mss_now;
980 struct rate_sample *rate;
983 /* Take a notice that peer is sending D-SACKs. Skip update of data delivery
984 * and spurious retransmission information if this DSACK is unlikely caused by
986 * - DSACKed sequence range is larger than maximum receiver's window.
987 * - Total no. of DSACKed segments exceed the total no. of retransmitted segs.
989 static u32 tcp_dsack_seen(struct tcp_sock *tp, u32 start_seq,
990 u32 end_seq, struct tcp_sacktag_state *state)
992 u32 seq_len, dup_segs = 1;
994 if (!before(start_seq, end_seq))
997 seq_len = end_seq - start_seq;
998 /* Dubious DSACK: DSACKed range greater than maximum advertised rwnd */
999 if (seq_len > tp->max_window)
1001 if (seq_len > tp->mss_cache)
1002 dup_segs = DIV_ROUND_UP(seq_len, tp->mss_cache);
1003 else if (tp->tlp_high_seq && tp->tlp_high_seq == end_seq)
1004 state->flag |= FLAG_DSACK_TLP;
1006 tp->dsack_dups += dup_segs;
1007 /* Skip the DSACK if dup segs weren't retransmitted by sender */
1008 if (tp->dsack_dups > tp->total_retrans)
1011 tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
1012 /* We increase the RACK ordering window in rounds where we receive
1013 * DSACKs that may have been due to reordering causing RACK to trigger
1014 * a spurious fast recovery. Thus RACK ignores DSACKs that happen
1015 * without having seen reordering, or that match TLP probes (TLP
1016 * is timer-driven, not triggered by RACK).
1018 if (tp->reord_seen && !(state->flag & FLAG_DSACK_TLP))
1019 tp->rack.dsack_seen = 1;
1021 state->flag |= FLAG_DSACKING_ACK;
1022 /* A spurious retransmission is delivered */
1023 state->sack_delivered += dup_segs;
1028 /* It's reordering when higher sequence was delivered (i.e. sacked) before
1029 * some lower never-retransmitted sequence ("low_seq"). The maximum reordering
1030 * distance is approximated in full-mss packet distance ("reordering").
1032 static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq,
1035 struct tcp_sock *tp = tcp_sk(sk);
1036 const u32 mss = tp->mss_cache;
1039 fack = tcp_highest_sack_seq(tp);
1040 if (!before(low_seq, fack))
1043 metric = fack - low_seq;
1044 if ((metric > tp->reordering * mss) && mss) {
1045 #if FASTRETRANS_DEBUG > 1
1046 pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
1047 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
1051 tp->undo_marker ? tp->undo_retrans : 0);
1053 tp->reordering = min_t(u32, (metric + mss - 1) / mss,
1054 sock_net(sk)->ipv4.sysctl_tcp_max_reordering);
1057 /* This exciting event is worth to be remembered. 8) */
1059 NET_INC_STATS(sock_net(sk),
1060 ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER);
1063 /* This must be called before lost_out or retrans_out are updated
1064 * on a new loss, because we want to know if all skbs previously
1065 * known to be lost have already been retransmitted, indicating
1066 * that this newly lost skb is our next skb to retransmit.
1068 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
1070 if ((!tp->retransmit_skb_hint && tp->retrans_out >= tp->lost_out) ||
1071 (tp->retransmit_skb_hint &&
1072 before(TCP_SKB_CB(skb)->seq,
1073 TCP_SKB_CB(tp->retransmit_skb_hint)->seq)))
1074 tp->retransmit_skb_hint = skb;
1077 /* Sum the number of packets on the wire we have marked as lost, and
1078 * notify the congestion control module that the given skb was marked lost.
1080 static void tcp_notify_skb_loss_event(struct tcp_sock *tp, const struct sk_buff *skb)
1082 tp->lost += tcp_skb_pcount(skb);
1085 void tcp_mark_skb_lost(struct sock *sk, struct sk_buff *skb)
1087 __u8 sacked = TCP_SKB_CB(skb)->sacked;
1088 struct tcp_sock *tp = tcp_sk(sk);
1090 if (sacked & TCPCB_SACKED_ACKED)
1093 tcp_verify_retransmit_hint(tp, skb);
1094 if (sacked & TCPCB_LOST) {
1095 if (sacked & TCPCB_SACKED_RETRANS) {
1096 /* Account for retransmits that are lost again */
1097 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1098 tp->retrans_out -= tcp_skb_pcount(skb);
1099 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT,
1100 tcp_skb_pcount(skb));
1101 tcp_notify_skb_loss_event(tp, skb);
1104 tp->lost_out += tcp_skb_pcount(skb);
1105 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1106 tcp_notify_skb_loss_event(tp, skb);
1110 /* Updates the delivered and delivered_ce counts */
1111 static void tcp_count_delivered(struct tcp_sock *tp, u32 delivered,
1114 tp->delivered += delivered;
1116 tp->delivered_ce += delivered;
1119 /* This procedure tags the retransmission queue when SACKs arrive.
1121 * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
1122 * Packets in queue with these bits set are counted in variables
1123 * sacked_out, retrans_out and lost_out, correspondingly.
1125 * Valid combinations are:
1126 * Tag InFlight Description
1127 * 0 1 - orig segment is in flight.
1128 * S 0 - nothing flies, orig reached receiver.
1129 * L 0 - nothing flies, orig lost by net.
1130 * R 2 - both orig and retransmit are in flight.
1131 * L|R 1 - orig is lost, retransmit is in flight.
1132 * S|R 1 - orig reached receiver, retrans is still in flight.
1133 * (L|S|R is logically valid, it could occur when L|R is sacked,
1134 * but it is equivalent to plain S and code short-curcuits it to S.
1135 * L|S is logically invalid, it would mean -1 packet in flight 8))
1137 * These 6 states form finite state machine, controlled by the following events:
1138 * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
1139 * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
1140 * 3. Loss detection event of two flavors:
1141 * A. Scoreboard estimator decided the packet is lost.
1142 * A'. Reno "three dupacks" marks head of queue lost.
1143 * B. SACK arrives sacking SND.NXT at the moment, when the
1144 * segment was retransmitted.
1145 * 4. D-SACK added new rule: D-SACK changes any tag to S.
1147 * It is pleasant to note, that state diagram turns out to be commutative,
1148 * so that we are allowed not to be bothered by order of our actions,
1149 * when multiple events arrive simultaneously. (see the function below).
1151 * Reordering detection.
1152 * --------------------
1153 * Reordering metric is maximal distance, which a packet can be displaced
1154 * in packet stream. With SACKs we can estimate it:
1156 * 1. SACK fills old hole and the corresponding segment was not
1157 * ever retransmitted -> reordering. Alas, we cannot use it
1158 * when segment was retransmitted.
1159 * 2. The last flaw is solved with D-SACK. D-SACK arrives
1160 * for retransmitted and already SACKed segment -> reordering..
1161 * Both of these heuristics are not used in Loss state, when we cannot
1162 * account for retransmits accurately.
1164 * SACK block validation.
1165 * ----------------------
1167 * SACK block range validation checks that the received SACK block fits to
1168 * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1169 * Note that SND.UNA is not included to the range though being valid because
1170 * it means that the receiver is rather inconsistent with itself reporting
1171 * SACK reneging when it should advance SND.UNA. Such SACK block this is
1172 * perfectly valid, however, in light of RFC2018 which explicitly states
1173 * that "SACK block MUST reflect the newest segment. Even if the newest
1174 * segment is going to be discarded ...", not that it looks very clever
1175 * in case of head skb. Due to potentional receiver driven attacks, we
1176 * choose to avoid immediate execution of a walk in write queue due to
1177 * reneging and defer head skb's loss recovery to standard loss recovery
1178 * procedure that will eventually trigger (nothing forbids us doing this).
1180 * Implements also blockage to start_seq wrap-around. Problem lies in the
1181 * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1182 * there's no guarantee that it will be before snd_nxt (n). The problem
1183 * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1186 * <- outs wnd -> <- wrapzone ->
1187 * u e n u_w e_w s n_w
1189 * |<------------+------+----- TCP seqno space --------------+---------->|
1190 * ...-- <2^31 ->| |<--------...
1191 * ...---- >2^31 ------>| |<--------...
1193 * Current code wouldn't be vulnerable but it's better still to discard such
1194 * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1195 * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1196 * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1197 * equal to the ideal case (infinite seqno space without wrap caused issues).
1199 * With D-SACK the lower bound is extended to cover sequence space below
1200 * SND.UNA down to undo_marker, which is the last point of interest. Yet
1201 * again, D-SACK block must not to go across snd_una (for the same reason as
1202 * for the normal SACK blocks, explained above). But there all simplicity
1203 * ends, TCP might receive valid D-SACKs below that. As long as they reside
1204 * fully below undo_marker they do not affect behavior in anyway and can
1205 * therefore be safely ignored. In rare cases (which are more or less
1206 * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1207 * fragmentation and packet reordering past skb's retransmission. To consider
1208 * them correctly, the acceptable range must be extended even more though
1209 * the exact amount is rather hard to quantify. However, tp->max_window can
1210 * be used as an exaggerated estimate.
1212 static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
1213 u32 start_seq, u32 end_seq)
1215 /* Too far in future, or reversed (interpretation is ambiguous) */
1216 if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1219 /* Nasty start_seq wrap-around check (see comments above) */
1220 if (!before(start_seq, tp->snd_nxt))
1223 /* In outstanding window? ...This is valid exit for D-SACKs too.
1224 * start_seq == snd_una is non-sensical (see comments above)
1226 if (after(start_seq, tp->snd_una))
1229 if (!is_dsack || !tp->undo_marker)
1232 /* ...Then it's D-SACK, and must reside below snd_una completely */
1233 if (after(end_seq, tp->snd_una))
1236 if (!before(start_seq, tp->undo_marker))
1240 if (!after(end_seq, tp->undo_marker))
1243 /* Undo_marker boundary crossing (overestimates a lot). Known already:
1244 * start_seq < undo_marker and end_seq >= undo_marker.
1246 return !before(start_seq, end_seq - tp->max_window);
1249 static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1250 struct tcp_sack_block_wire *sp, int num_sacks,
1251 u32 prior_snd_una, struct tcp_sacktag_state *state)
1253 struct tcp_sock *tp = tcp_sk(sk);
1254 u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1255 u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1258 if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1259 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1260 } else if (num_sacks > 1) {
1261 u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1262 u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1264 if (after(end_seq_0, end_seq_1) || before(start_seq_0, start_seq_1))
1266 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKOFORECV);
1271 dup_segs = tcp_dsack_seen(tp, start_seq_0, end_seq_0, state);
1272 if (!dup_segs) { /* Skip dubious DSACK */
1273 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKIGNOREDDUBIOUS);
1277 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECVSEGS, dup_segs);
1279 /* D-SACK for already forgotten data... Do dumb counting. */
1280 if (tp->undo_marker && tp->undo_retrans > 0 &&
1281 !after(end_seq_0, prior_snd_una) &&
1282 after(end_seq_0, tp->undo_marker))
1283 tp->undo_retrans = max_t(int, 0, tp->undo_retrans - dup_segs);
1288 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1289 * the incoming SACK may not exactly match but we can find smaller MSS
1290 * aligned portion of it that matches. Therefore we might need to fragment
1291 * which may fail and creates some hassle (caller must handle error case
1294 * FIXME: this could be merged to shift decision code
1296 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1297 u32 start_seq, u32 end_seq)
1301 unsigned int pkt_len;
1304 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1305 !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1307 if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1308 after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1309 mss = tcp_skb_mss(skb);
1310 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1313 pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1317 pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1322 /* Round if necessary so that SACKs cover only full MSSes
1323 * and/or the remaining small portion (if present)
1325 if (pkt_len > mss) {
1326 unsigned int new_len = (pkt_len / mss) * mss;
1327 if (!in_sack && new_len < pkt_len)
1332 if (pkt_len >= skb->len && !in_sack)
1335 err = tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
1336 pkt_len, mss, GFP_ATOMIC);
1344 /* Mark the given newly-SACKed range as such, adjusting counters and hints. */
1345 static u8 tcp_sacktag_one(struct sock *sk,
1346 struct tcp_sacktag_state *state, u8 sacked,
1347 u32 start_seq, u32 end_seq,
1348 int dup_sack, int pcount,
1351 struct tcp_sock *tp = tcp_sk(sk);
1353 /* Account D-SACK for retransmitted packet. */
1354 if (dup_sack && (sacked & TCPCB_RETRANS)) {
1355 if (tp->undo_marker && tp->undo_retrans > 0 &&
1356 after(end_seq, tp->undo_marker))
1357 tp->undo_retrans = max_t(int, 0, tp->undo_retrans - pcount);
1358 if ((sacked & TCPCB_SACKED_ACKED) &&
1359 before(start_seq, state->reord))
1360 state->reord = start_seq;
1363 /* Nothing to do; acked frame is about to be dropped (was ACKed). */
1364 if (!after(end_seq, tp->snd_una))
1367 if (!(sacked & TCPCB_SACKED_ACKED)) {
1368 tcp_rack_advance(tp, sacked, end_seq, xmit_time);
1370 if (sacked & TCPCB_SACKED_RETRANS) {
1371 /* If the segment is not tagged as lost,
1372 * we do not clear RETRANS, believing
1373 * that retransmission is still in flight.
1375 if (sacked & TCPCB_LOST) {
1376 sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1377 tp->lost_out -= pcount;
1378 tp->retrans_out -= pcount;
1381 if (!(sacked & TCPCB_RETRANS)) {
1382 /* New sack for not retransmitted frame,
1383 * which was in hole. It is reordering.
1385 if (before(start_seq,
1386 tcp_highest_sack_seq(tp)) &&
1387 before(start_seq, state->reord))
1388 state->reord = start_seq;
1390 if (!after(end_seq, tp->high_seq))
1391 state->flag |= FLAG_ORIG_SACK_ACKED;
1392 if (state->first_sackt == 0)
1393 state->first_sackt = xmit_time;
1394 state->last_sackt = xmit_time;
1397 if (sacked & TCPCB_LOST) {
1398 sacked &= ~TCPCB_LOST;
1399 tp->lost_out -= pcount;
1403 sacked |= TCPCB_SACKED_ACKED;
1404 state->flag |= FLAG_DATA_SACKED;
1405 tp->sacked_out += pcount;
1406 /* Out-of-order packets delivered */
1407 state->sack_delivered += pcount;
1409 /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1410 if (tp->lost_skb_hint &&
1411 before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1412 tp->lost_cnt_hint += pcount;
1415 /* D-SACK. We can detect redundant retransmission in S|R and plain R
1416 * frames and clear it. undo_retrans is decreased above, L|R frames
1417 * are accounted above as well.
1419 if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1420 sacked &= ~TCPCB_SACKED_RETRANS;
1421 tp->retrans_out -= pcount;
1427 /* Shift newly-SACKed bytes from this skb to the immediately previous
1428 * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1430 static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev,
1431 struct sk_buff *skb,
1432 struct tcp_sacktag_state *state,
1433 unsigned int pcount, int shifted, int mss,
1436 struct tcp_sock *tp = tcp_sk(sk);
1437 u32 start_seq = TCP_SKB_CB(skb)->seq; /* start of newly-SACKed */
1438 u32 end_seq = start_seq + shifted; /* end of newly-SACKed */
1442 /* Adjust counters and hints for the newly sacked sequence
1443 * range but discard the return value since prev is already
1444 * marked. We must tag the range first because the seq
1445 * advancement below implicitly advances
1446 * tcp_highest_sack_seq() when skb is highest_sack.
1448 tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1449 start_seq, end_seq, dup_sack, pcount,
1450 tcp_skb_timestamp_us(skb));
1451 tcp_rate_skb_delivered(sk, skb, state->rate);
1453 if (skb == tp->lost_skb_hint)
1454 tp->lost_cnt_hint += pcount;
1456 TCP_SKB_CB(prev)->end_seq += shifted;
1457 TCP_SKB_CB(skb)->seq += shifted;
1459 tcp_skb_pcount_add(prev, pcount);
1460 WARN_ON_ONCE(tcp_skb_pcount(skb) < pcount);
1461 tcp_skb_pcount_add(skb, -pcount);
1463 /* When we're adding to gso_segs == 1, gso_size will be zero,
1464 * in theory this shouldn't be necessary but as long as DSACK
1465 * code can come after this skb later on it's better to keep
1466 * setting gso_size to something.
1468 if (!TCP_SKB_CB(prev)->tcp_gso_size)
1469 TCP_SKB_CB(prev)->tcp_gso_size = mss;
1471 /* CHECKME: To clear or not to clear? Mimics normal skb currently */
1472 if (tcp_skb_pcount(skb) <= 1)
1473 TCP_SKB_CB(skb)->tcp_gso_size = 0;
1475 /* Difference in this won't matter, both ACKed by the same cumul. ACK */
1476 TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1479 BUG_ON(!tcp_skb_pcount(skb));
1480 NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1484 /* Whole SKB was eaten :-) */
1486 if (skb == tp->retransmit_skb_hint)
1487 tp->retransmit_skb_hint = prev;
1488 if (skb == tp->lost_skb_hint) {
1489 tp->lost_skb_hint = prev;
1490 tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1493 TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1494 TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
1495 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1496 TCP_SKB_CB(prev)->end_seq++;
1498 if (skb == tcp_highest_sack(sk))
1499 tcp_advance_highest_sack(sk, skb);
1501 tcp_skb_collapse_tstamp(prev, skb);
1502 if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp))
1503 TCP_SKB_CB(prev)->tx.delivered_mstamp = 0;
1505 tcp_rtx_queue_unlink_and_free(skb, sk);
1507 NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED);
1512 /* I wish gso_size would have a bit more sane initialization than
1513 * something-or-zero which complicates things
1515 static int tcp_skb_seglen(const struct sk_buff *skb)
1517 return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1520 /* Shifting pages past head area doesn't work */
1521 static int skb_can_shift(const struct sk_buff *skb)
1523 return !skb_headlen(skb) && skb_is_nonlinear(skb);
1526 int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from,
1527 int pcount, int shiftlen)
1529 /* TCP min gso_size is 8 bytes (TCP_MIN_GSO_SIZE)
1530 * Since TCP_SKB_CB(skb)->tcp_gso_segs is 16 bits, we need
1531 * to make sure not storing more than 65535 * 8 bytes per skb,
1532 * even if current MSS is bigger.
1534 if (unlikely(to->len + shiftlen >= 65535 * TCP_MIN_GSO_SIZE))
1536 if (unlikely(tcp_skb_pcount(to) + pcount > 65535))
1538 return skb_shift(to, from, shiftlen);
1541 /* Try collapsing SACK blocks spanning across multiple skbs to a single
1544 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1545 struct tcp_sacktag_state *state,
1546 u32 start_seq, u32 end_seq,
1549 struct tcp_sock *tp = tcp_sk(sk);
1550 struct sk_buff *prev;
1556 /* Normally R but no L won't result in plain S */
1558 (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1560 if (!skb_can_shift(skb))
1562 /* This frame is about to be dropped (was ACKed). */
1563 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1566 /* Can only happen with delayed DSACK + discard craziness */
1567 prev = skb_rb_prev(skb);
1571 if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1574 if (!tcp_skb_can_collapse(prev, skb))
1577 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1578 !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1582 pcount = tcp_skb_pcount(skb);
1583 mss = tcp_skb_seglen(skb);
1585 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1586 * drop this restriction as unnecessary
1588 if (mss != tcp_skb_seglen(prev))
1591 if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1593 /* CHECKME: This is non-MSS split case only?, this will
1594 * cause skipped skbs due to advancing loop btw, original
1595 * has that feature too
1597 if (tcp_skb_pcount(skb) <= 1)
1600 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1602 /* TODO: head merge to next could be attempted here
1603 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1604 * though it might not be worth of the additional hassle
1606 * ...we can probably just fallback to what was done
1607 * previously. We could try merging non-SACKed ones
1608 * as well but it probably isn't going to buy off
1609 * because later SACKs might again split them, and
1610 * it would make skb timestamp tracking considerably
1616 len = end_seq - TCP_SKB_CB(skb)->seq;
1618 BUG_ON(len > skb->len);
1620 /* MSS boundaries should be honoured or else pcount will
1621 * severely break even though it makes things bit trickier.
1622 * Optimize common case to avoid most of the divides
1624 mss = tcp_skb_mss(skb);
1626 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1627 * drop this restriction as unnecessary
1629 if (mss != tcp_skb_seglen(prev))
1634 } else if (len < mss) {
1642 /* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1643 if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1646 if (!tcp_skb_shift(prev, skb, pcount, len))
1648 if (!tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, dup_sack))
1651 /* Hole filled allows collapsing with the next as well, this is very
1652 * useful when hole on every nth skb pattern happens
1654 skb = skb_rb_next(prev);
1658 if (!skb_can_shift(skb) ||
1659 ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1660 (mss != tcp_skb_seglen(skb)))
1663 if (!tcp_skb_can_collapse(prev, skb))
1666 pcount = tcp_skb_pcount(skb);
1667 if (tcp_skb_shift(prev, skb, pcount, len))
1668 tcp_shifted_skb(sk, prev, skb, state, pcount,
1678 NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1682 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1683 struct tcp_sack_block *next_dup,
1684 struct tcp_sacktag_state *state,
1685 u32 start_seq, u32 end_seq,
1688 struct tcp_sock *tp = tcp_sk(sk);
1689 struct sk_buff *tmp;
1691 skb_rbtree_walk_from(skb) {
1693 bool dup_sack = dup_sack_in;
1695 /* queue is in-order => we can short-circuit the walk early */
1696 if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1700 before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1701 in_sack = tcp_match_skb_to_sack(sk, skb,
1702 next_dup->start_seq,
1708 /* skb reference here is a bit tricky to get right, since
1709 * shifting can eat and free both this skb and the next,
1710 * so not even _safe variant of the loop is enough.
1713 tmp = tcp_shift_skb_data(sk, skb, state,
1714 start_seq, end_seq, dup_sack);
1723 in_sack = tcp_match_skb_to_sack(sk, skb,
1729 if (unlikely(in_sack < 0))
1733 TCP_SKB_CB(skb)->sacked =
1736 TCP_SKB_CB(skb)->sacked,
1737 TCP_SKB_CB(skb)->seq,
1738 TCP_SKB_CB(skb)->end_seq,
1740 tcp_skb_pcount(skb),
1741 tcp_skb_timestamp_us(skb));
1742 tcp_rate_skb_delivered(sk, skb, state->rate);
1743 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1744 list_del_init(&skb->tcp_tsorted_anchor);
1746 if (!before(TCP_SKB_CB(skb)->seq,
1747 tcp_highest_sack_seq(tp)))
1748 tcp_advance_highest_sack(sk, skb);
1754 static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk, u32 seq)
1756 struct rb_node *parent, **p = &sk->tcp_rtx_queue.rb_node;
1757 struct sk_buff *skb;
1761 skb = rb_to_skb(parent);
1762 if (before(seq, TCP_SKB_CB(skb)->seq)) {
1763 p = &parent->rb_left;
1766 if (!before(seq, TCP_SKB_CB(skb)->end_seq)) {
1767 p = &parent->rb_right;
1775 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1778 if (skb && after(TCP_SKB_CB(skb)->seq, skip_to_seq))
1781 return tcp_sacktag_bsearch(sk, skip_to_seq);
1784 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1786 struct tcp_sack_block *next_dup,
1787 struct tcp_sacktag_state *state,
1793 if (before(next_dup->start_seq, skip_to_seq)) {
1794 skb = tcp_sacktag_skip(skb, sk, next_dup->start_seq);
1795 skb = tcp_sacktag_walk(skb, sk, NULL, state,
1796 next_dup->start_seq, next_dup->end_seq,
1803 static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1805 return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1809 tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1810 u32 prior_snd_una, struct tcp_sacktag_state *state)
1812 struct tcp_sock *tp = tcp_sk(sk);
1813 const unsigned char *ptr = (skb_transport_header(ack_skb) +
1814 TCP_SKB_CB(ack_skb)->sacked);
1815 struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1816 struct tcp_sack_block sp[TCP_NUM_SACKS];
1817 struct tcp_sack_block *cache;
1818 struct sk_buff *skb;
1819 int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1821 bool found_dup_sack = false;
1823 int first_sack_index;
1826 state->reord = tp->snd_nxt;
1828 if (!tp->sacked_out)
1829 tcp_highest_sack_reset(sk);
1831 found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1832 num_sacks, prior_snd_una, state);
1834 /* Eliminate too old ACKs, but take into
1835 * account more or less fresh ones, they can
1836 * contain valid SACK info.
1838 if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1841 if (!tp->packets_out)
1845 first_sack_index = 0;
1846 for (i = 0; i < num_sacks; i++) {
1847 bool dup_sack = !i && found_dup_sack;
1849 sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1850 sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1852 if (!tcp_is_sackblock_valid(tp, dup_sack,
1853 sp[used_sacks].start_seq,
1854 sp[used_sacks].end_seq)) {
1858 if (!tp->undo_marker)
1859 mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1861 mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1863 /* Don't count olds caused by ACK reordering */
1864 if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1865 !after(sp[used_sacks].end_seq, tp->snd_una))
1867 mib_idx = LINUX_MIB_TCPSACKDISCARD;
1870 NET_INC_STATS(sock_net(sk), mib_idx);
1872 first_sack_index = -1;
1876 /* Ignore very old stuff early */
1877 if (!after(sp[used_sacks].end_seq, prior_snd_una)) {
1879 first_sack_index = -1;
1886 /* order SACK blocks to allow in order walk of the retrans queue */
1887 for (i = used_sacks - 1; i > 0; i--) {
1888 for (j = 0; j < i; j++) {
1889 if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1890 swap(sp[j], sp[j + 1]);
1892 /* Track where the first SACK block goes to */
1893 if (j == first_sack_index)
1894 first_sack_index = j + 1;
1899 state->mss_now = tcp_current_mss(sk);
1903 if (!tp->sacked_out) {
1904 /* It's already past, so skip checking against it */
1905 cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1907 cache = tp->recv_sack_cache;
1908 /* Skip empty blocks in at head of the cache */
1909 while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1914 while (i < used_sacks) {
1915 u32 start_seq = sp[i].start_seq;
1916 u32 end_seq = sp[i].end_seq;
1917 bool dup_sack = (found_dup_sack && (i == first_sack_index));
1918 struct tcp_sack_block *next_dup = NULL;
1920 if (found_dup_sack && ((i + 1) == first_sack_index))
1921 next_dup = &sp[i + 1];
1923 /* Skip too early cached blocks */
1924 while (tcp_sack_cache_ok(tp, cache) &&
1925 !before(start_seq, cache->end_seq))
1928 /* Can skip some work by looking recv_sack_cache? */
1929 if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1930 after(end_seq, cache->start_seq)) {
1933 if (before(start_seq, cache->start_seq)) {
1934 skb = tcp_sacktag_skip(skb, sk, start_seq);
1935 skb = tcp_sacktag_walk(skb, sk, next_dup,
1942 /* Rest of the block already fully processed? */
1943 if (!after(end_seq, cache->end_seq))
1946 skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1950 /* ...tail remains todo... */
1951 if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1952 /* ...but better entrypoint exists! */
1953 skb = tcp_highest_sack(sk);
1960 skb = tcp_sacktag_skip(skb, sk, cache->end_seq);
1961 /* Check overlap against next cached too (past this one already) */
1966 if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1967 skb = tcp_highest_sack(sk);
1971 skb = tcp_sacktag_skip(skb, sk, start_seq);
1974 skb = tcp_sacktag_walk(skb, sk, next_dup, state,
1975 start_seq, end_seq, dup_sack);
1981 /* Clear the head of the cache sack blocks so we can skip it next time */
1982 for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1983 tp->recv_sack_cache[i].start_seq = 0;
1984 tp->recv_sack_cache[i].end_seq = 0;
1986 for (j = 0; j < used_sacks; j++)
1987 tp->recv_sack_cache[i++] = sp[j];
1989 if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss || tp->undo_marker)
1990 tcp_check_sack_reordering(sk, state->reord, 0);
1992 tcp_verify_left_out(tp);
1995 #if FASTRETRANS_DEBUG > 0
1996 WARN_ON((int)tp->sacked_out < 0);
1997 WARN_ON((int)tp->lost_out < 0);
1998 WARN_ON((int)tp->retrans_out < 0);
1999 WARN_ON((int)tcp_packets_in_flight(tp) < 0);
2004 /* Limits sacked_out so that sum with lost_out isn't ever larger than
2005 * packets_out. Returns false if sacked_out adjustement wasn't necessary.
2007 static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
2011 holes = max(tp->lost_out, 1U);
2012 holes = min(holes, tp->packets_out);
2014 if ((tp->sacked_out + holes) > tp->packets_out) {
2015 tp->sacked_out = tp->packets_out - holes;
2021 /* If we receive more dupacks than we expected counting segments
2022 * in assumption of absent reordering, interpret this as reordering.
2023 * The only another reason could be bug in receiver TCP.
2025 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
2027 struct tcp_sock *tp = tcp_sk(sk);
2029 if (!tcp_limit_reno_sacked(tp))
2032 tp->reordering = min_t(u32, tp->packets_out + addend,
2033 sock_net(sk)->ipv4.sysctl_tcp_max_reordering);
2035 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRENOREORDER);
2038 /* Emulate SACKs for SACKless connection: account for a new dupack. */
2040 static void tcp_add_reno_sack(struct sock *sk, int num_dupack, bool ece_ack)
2043 struct tcp_sock *tp = tcp_sk(sk);
2044 u32 prior_sacked = tp->sacked_out;
2047 tp->sacked_out += num_dupack;
2048 tcp_check_reno_reordering(sk, 0);
2049 delivered = tp->sacked_out - prior_sacked;
2051 tcp_count_delivered(tp, delivered, ece_ack);
2052 tcp_verify_left_out(tp);
2056 /* Account for ACK, ACKing some data in Reno Recovery phase. */
2058 static void tcp_remove_reno_sacks(struct sock *sk, int acked, bool ece_ack)
2060 struct tcp_sock *tp = tcp_sk(sk);
2063 /* One ACK acked hole. The rest eat duplicate ACKs. */
2064 tcp_count_delivered(tp, max_t(int, acked - tp->sacked_out, 1),
2066 if (acked - 1 >= tp->sacked_out)
2069 tp->sacked_out -= acked - 1;
2071 tcp_check_reno_reordering(sk, acked);
2072 tcp_verify_left_out(tp);
2075 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
2080 void tcp_clear_retrans(struct tcp_sock *tp)
2082 tp->retrans_out = 0;
2084 tp->undo_marker = 0;
2085 tp->undo_retrans = -1;
2089 static inline void tcp_init_undo(struct tcp_sock *tp)
2091 tp->undo_marker = tp->snd_una;
2092 /* Retransmission still in flight may cause DSACKs later. */
2093 tp->undo_retrans = tp->retrans_out ? : -1;
2096 static bool tcp_is_rack(const struct sock *sk)
2098 return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_recovery) &
2099 TCP_RACK_LOSS_DETECTION;
2102 /* If we detect SACK reneging, forget all SACK information
2103 * and reset tags completely, otherwise preserve SACKs. If receiver
2104 * dropped its ofo queue, we will know this due to reneging detection.
2106 static void tcp_timeout_mark_lost(struct sock *sk)
2108 struct tcp_sock *tp = tcp_sk(sk);
2109 struct sk_buff *skb, *head;
2110 bool is_reneg; /* is receiver reneging on SACKs? */
2112 head = tcp_rtx_queue_head(sk);
2113 is_reneg = head && (TCP_SKB_CB(head)->sacked & TCPCB_SACKED_ACKED);
2115 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
2117 /* Mark SACK reneging until we recover from this loss event. */
2118 tp->is_sack_reneg = 1;
2119 } else if (tcp_is_reno(tp)) {
2120 tcp_reset_reno_sack(tp);
2124 skb_rbtree_walk_from(skb) {
2126 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
2127 else if (tcp_is_rack(sk) && skb != head &&
2128 tcp_rack_skb_timeout(tp, skb, 0) > 0)
2129 continue; /* Don't mark recently sent ones lost yet */
2130 tcp_mark_skb_lost(sk, skb);
2132 tcp_verify_left_out(tp);
2133 tcp_clear_all_retrans_hints(tp);
2136 /* Enter Loss state. */
2137 void tcp_enter_loss(struct sock *sk)
2139 const struct inet_connection_sock *icsk = inet_csk(sk);
2140 struct tcp_sock *tp = tcp_sk(sk);
2141 struct net *net = sock_net(sk);
2142 bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
2145 tcp_timeout_mark_lost(sk);
2147 /* Reduce ssthresh if it has not yet been made inside this window. */
2148 if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
2149 !after(tp->high_seq, tp->snd_una) ||
2150 (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
2151 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2152 tp->prior_cwnd = tcp_snd_cwnd(tp);
2153 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2154 tcp_ca_event(sk, CA_EVENT_LOSS);
2157 tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + 1);
2158 tp->snd_cwnd_cnt = 0;
2159 tp->snd_cwnd_stamp = tcp_jiffies32;
2161 /* Timeout in disordered state after receiving substantial DUPACKs
2162 * suggests that the degree of reordering is over-estimated.
2164 reordering = READ_ONCE(net->ipv4.sysctl_tcp_reordering);
2165 if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
2166 tp->sacked_out >= reordering)
2167 tp->reordering = min_t(unsigned int, tp->reordering,
2170 tcp_set_ca_state(sk, TCP_CA_Loss);
2171 tp->high_seq = tp->snd_nxt;
2172 tcp_ecn_queue_cwr(tp);
2174 /* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
2175 * loss recovery is underway except recurring timeout(s) on
2176 * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
2178 tp->frto = net->ipv4.sysctl_tcp_frto &&
2179 (new_recovery || icsk->icsk_retransmits) &&
2180 !inet_csk(sk)->icsk_mtup.probe_size;
2183 /* If ACK arrived pointing to a remembered SACK, it means that our
2184 * remembered SACKs do not reflect real state of receiver i.e.
2185 * receiver _host_ is heavily congested (or buggy).
2187 * To avoid big spurious retransmission bursts due to transient SACK
2188 * scoreboard oddities that look like reneging, we give the receiver a
2189 * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
2190 * restore sanity to the SACK scoreboard. If the apparent reneging
2191 * persists until this RTO then we'll clear the SACK scoreboard.
2193 static bool tcp_check_sack_reneging(struct sock *sk, int flag)
2195 if (flag & FLAG_SACK_RENEGING) {
2196 struct tcp_sock *tp = tcp_sk(sk);
2197 unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
2198 msecs_to_jiffies(10));
2200 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2201 delay, TCP_RTO_MAX);
2207 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2208 * counter when SACK is enabled (without SACK, sacked_out is used for
2211 * With reordering, holes may still be in flight, so RFC3517 recovery
2212 * uses pure sacked_out (total number of SACKed segments) even though
2213 * it violates the RFC that uses duplicate ACKs, often these are equal
2214 * but when e.g. out-of-window ACKs or packet duplication occurs,
2215 * they differ. Since neither occurs due to loss, TCP should really
2218 static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
2220 return tp->sacked_out + 1;
2223 /* Linux NewReno/SACK/ECN state machine.
2224 * --------------------------------------
2226 * "Open" Normal state, no dubious events, fast path.
2227 * "Disorder" In all the respects it is "Open",
2228 * but requires a bit more attention. It is entered when
2229 * we see some SACKs or dupacks. It is split of "Open"
2230 * mainly to move some processing from fast path to slow one.
2231 * "CWR" CWND was reduced due to some Congestion Notification event.
2232 * It can be ECN, ICMP source quench, local device congestion.
2233 * "Recovery" CWND was reduced, we are fast-retransmitting.
2234 * "Loss" CWND was reduced due to RTO timeout or SACK reneging.
2236 * tcp_fastretrans_alert() is entered:
2237 * - each incoming ACK, if state is not "Open"
2238 * - when arrived ACK is unusual, namely:
2243 * Counting packets in flight is pretty simple.
2245 * in_flight = packets_out - left_out + retrans_out
2247 * packets_out is SND.NXT-SND.UNA counted in packets.
2249 * retrans_out is number of retransmitted segments.
2251 * left_out is number of segments left network, but not ACKed yet.
2253 * left_out = sacked_out + lost_out
2255 * sacked_out: Packets, which arrived to receiver out of order
2256 * and hence not ACKed. With SACKs this number is simply
2257 * amount of SACKed data. Even without SACKs
2258 * it is easy to give pretty reliable estimate of this number,
2259 * counting duplicate ACKs.
2261 * lost_out: Packets lost by network. TCP has no explicit
2262 * "loss notification" feedback from network (for now).
2263 * It means that this number can be only _guessed_.
2264 * Actually, it is the heuristics to predict lossage that
2265 * distinguishes different algorithms.
2267 * F.e. after RTO, when all the queue is considered as lost,
2268 * lost_out = packets_out and in_flight = retrans_out.
2270 * Essentially, we have now a few algorithms detecting
2273 * If the receiver supports SACK:
2275 * RFC6675/3517: It is the conventional algorithm. A packet is
2276 * considered lost if the number of higher sequence packets
2277 * SACKed is greater than or equal the DUPACK thoreshold
2278 * (reordering). This is implemented in tcp_mark_head_lost and
2279 * tcp_update_scoreboard.
2281 * RACK (draft-ietf-tcpm-rack-01): it is a newer algorithm
2282 * (2017-) that checks timing instead of counting DUPACKs.
2283 * Essentially a packet is considered lost if it's not S/ACKed
2284 * after RTT + reordering_window, where both metrics are
2285 * dynamically measured and adjusted. This is implemented in
2286 * tcp_rack_mark_lost.
2288 * If the receiver does not support SACK:
2290 * NewReno (RFC6582): in Recovery we assume that one segment
2291 * is lost (classic Reno). While we are in Recovery and
2292 * a partial ACK arrives, we assume that one more packet
2293 * is lost (NewReno). This heuristics are the same in NewReno
2296 * Really tricky (and requiring careful tuning) part of algorithm
2297 * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2298 * The first determines the moment _when_ we should reduce CWND and,
2299 * hence, slow down forward transmission. In fact, it determines the moment
2300 * when we decide that hole is caused by loss, rather than by a reorder.
2302 * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2303 * holes, caused by lost packets.
2305 * And the most logically complicated part of algorithm is undo
2306 * heuristics. We detect false retransmits due to both too early
2307 * fast retransmit (reordering) and underestimated RTO, analyzing
2308 * timestamps and D-SACKs. When we detect that some segments were
2309 * retransmitted by mistake and CWND reduction was wrong, we undo
2310 * window reduction and abort recovery phase. This logic is hidden
2311 * inside several functions named tcp_try_undo_<something>.
2314 /* This function decides, when we should leave Disordered state
2315 * and enter Recovery phase, reducing congestion window.
2317 * Main question: may we further continue forward transmission
2318 * with the same cwnd?
2320 static bool tcp_time_to_recover(struct sock *sk, int flag)
2322 struct tcp_sock *tp = tcp_sk(sk);
2324 /* Trick#1: The loss is proven. */
2328 /* Not-A-Trick#2 : Classic rule... */
2329 if (!tcp_is_rack(sk) && tcp_dupack_heuristics(tp) > tp->reordering)
2335 /* Detect loss in event "A" above by marking head of queue up as lost.
2336 * For RFC3517 SACK, a segment is considered lost if it
2337 * has at least tp->reordering SACKed seqments above it; "packets" refers to
2338 * the maximum SACKed segments to pass before reaching this limit.
2340 static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2342 struct tcp_sock *tp = tcp_sk(sk);
2343 struct sk_buff *skb;
2345 /* Use SACK to deduce losses of new sequences sent during recovery */
2346 const u32 loss_high = tp->snd_nxt;
2348 WARN_ON(packets > tp->packets_out);
2349 skb = tp->lost_skb_hint;
2351 /* Head already handled? */
2352 if (mark_head && after(TCP_SKB_CB(skb)->seq, tp->snd_una))
2354 cnt = tp->lost_cnt_hint;
2356 skb = tcp_rtx_queue_head(sk);
2360 skb_rbtree_walk_from(skb) {
2361 /* TODO: do this better */
2362 /* this is not the most efficient way to do this... */
2363 tp->lost_skb_hint = skb;
2364 tp->lost_cnt_hint = cnt;
2366 if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
2369 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2370 cnt += tcp_skb_pcount(skb);
2375 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_LOST))
2376 tcp_mark_skb_lost(sk, skb);
2381 tcp_verify_left_out(tp);
2384 /* Account newly detected lost packet(s) */
2386 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2388 struct tcp_sock *tp = tcp_sk(sk);
2390 if (tcp_is_sack(tp)) {
2391 int sacked_upto = tp->sacked_out - tp->reordering;
2392 if (sacked_upto >= 0)
2393 tcp_mark_head_lost(sk, sacked_upto, 0);
2394 else if (fast_rexmit)
2395 tcp_mark_head_lost(sk, 1, 1);
2399 static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
2401 return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2402 before(tp->rx_opt.rcv_tsecr, when);
2405 /* skb is spurious retransmitted if the returned timestamp echo
2406 * reply is prior to the skb transmission time
2408 static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
2409 const struct sk_buff *skb)
2411 return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) &&
2412 tcp_tsopt_ecr_before(tp, tcp_skb_timestamp(skb));
2415 /* Nothing was retransmitted or returned timestamp is less
2416 * than timestamp of the first retransmission.
2418 static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
2420 return tp->retrans_stamp &&
2421 tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
2424 /* Undo procedures. */
2426 /* We can clear retrans_stamp when there are no retransmissions in the
2427 * window. It would seem that it is trivially available for us in
2428 * tp->retrans_out, however, that kind of assumptions doesn't consider
2429 * what will happen if errors occur when sending retransmission for the
2430 * second time. ...It could the that such segment has only
2431 * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2432 * the head skb is enough except for some reneging corner cases that
2433 * are not worth the effort.
2435 * Main reason for all this complexity is the fact that connection dying
2436 * time now depends on the validity of the retrans_stamp, in particular,
2437 * that successive retransmissions of a segment must not advance
2438 * retrans_stamp under any conditions.
2440 static bool tcp_any_retrans_done(const struct sock *sk)
2442 const struct tcp_sock *tp = tcp_sk(sk);
2443 struct sk_buff *skb;
2445 if (tp->retrans_out)
2448 skb = tcp_rtx_queue_head(sk);
2449 if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2455 static void DBGUNDO(struct sock *sk, const char *msg)
2457 #if FASTRETRANS_DEBUG > 1
2458 struct tcp_sock *tp = tcp_sk(sk);
2459 struct inet_sock *inet = inet_sk(sk);
2461 if (sk->sk_family == AF_INET) {
2462 pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2464 &inet->inet_daddr, ntohs(inet->inet_dport),
2465 tcp_snd_cwnd(tp), tcp_left_out(tp),
2466 tp->snd_ssthresh, tp->prior_ssthresh,
2469 #if IS_ENABLED(CONFIG_IPV6)
2470 else if (sk->sk_family == AF_INET6) {
2471 pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2473 &sk->sk_v6_daddr, ntohs(inet->inet_dport),
2474 tcp_snd_cwnd(tp), tcp_left_out(tp),
2475 tp->snd_ssthresh, tp->prior_ssthresh,
2482 static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
2484 struct tcp_sock *tp = tcp_sk(sk);
2487 struct sk_buff *skb;
2489 skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2490 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2493 tcp_clear_all_retrans_hints(tp);
2496 if (tp->prior_ssthresh) {
2497 const struct inet_connection_sock *icsk = inet_csk(sk);
2499 tcp_snd_cwnd_set(tp, icsk->icsk_ca_ops->undo_cwnd(sk));
2501 if (tp->prior_ssthresh > tp->snd_ssthresh) {
2502 tp->snd_ssthresh = tp->prior_ssthresh;
2503 tcp_ecn_withdraw_cwr(tp);
2506 tp->snd_cwnd_stamp = tcp_jiffies32;
2507 tp->undo_marker = 0;
2508 tp->rack.advanced = 1; /* Force RACK to re-exam losses */
2511 static inline bool tcp_may_undo(const struct tcp_sock *tp)
2513 return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2516 /* People celebrate: "We love our President!" */
2517 static bool tcp_try_undo_recovery(struct sock *sk)
2519 struct tcp_sock *tp = tcp_sk(sk);
2521 if (tcp_may_undo(tp)) {
2524 /* Happy end! We did not retransmit anything
2525 * or our original transmission succeeded.
2527 DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2528 tcp_undo_cwnd_reduction(sk, false);
2529 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2530 mib_idx = LINUX_MIB_TCPLOSSUNDO;
2532 mib_idx = LINUX_MIB_TCPFULLUNDO;
2534 NET_INC_STATS(sock_net(sk), mib_idx);
2535 } else if (tp->rack.reo_wnd_persist) {
2536 tp->rack.reo_wnd_persist--;
2538 if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2539 /* Hold old state until something *above* high_seq
2540 * is ACKed. For Reno it is MUST to prevent false
2541 * fast retransmits (RFC2582). SACK TCP is safe. */
2542 if (!tcp_any_retrans_done(sk))
2543 tp->retrans_stamp = 0;
2546 tcp_set_ca_state(sk, TCP_CA_Open);
2547 tp->is_sack_reneg = 0;
2551 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2552 static bool tcp_try_undo_dsack(struct sock *sk)
2554 struct tcp_sock *tp = tcp_sk(sk);
2556 if (tp->undo_marker && !tp->undo_retrans) {
2557 tp->rack.reo_wnd_persist = min(TCP_RACK_RECOVERY_THRESH,
2558 tp->rack.reo_wnd_persist + 1);
2559 DBGUNDO(sk, "D-SACK");
2560 tcp_undo_cwnd_reduction(sk, false);
2561 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2567 /* Undo during loss recovery after partial ACK or using F-RTO. */
2568 static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
2570 struct tcp_sock *tp = tcp_sk(sk);
2572 if (frto_undo || tcp_may_undo(tp)) {
2573 tcp_undo_cwnd_reduction(sk, true);
2575 DBGUNDO(sk, "partial loss");
2576 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2578 NET_INC_STATS(sock_net(sk),
2579 LINUX_MIB_TCPSPURIOUSRTOS);
2580 inet_csk(sk)->icsk_retransmits = 0;
2581 if (frto_undo || tcp_is_sack(tp)) {
2582 tcp_set_ca_state(sk, TCP_CA_Open);
2583 tp->is_sack_reneg = 0;
2590 /* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
2591 * It computes the number of packets to send (sndcnt) based on packets newly
2593 * 1) If the packets in flight is larger than ssthresh, PRR spreads the
2594 * cwnd reductions across a full RTT.
2595 * 2) Otherwise PRR uses packet conservation to send as much as delivered.
2596 * But when SND_UNA is acked without further losses,
2597 * slow starts cwnd up to ssthresh to speed up the recovery.
2599 static void tcp_init_cwnd_reduction(struct sock *sk)
2601 struct tcp_sock *tp = tcp_sk(sk);
2603 tp->high_seq = tp->snd_nxt;
2604 tp->tlp_high_seq = 0;
2605 tp->snd_cwnd_cnt = 0;
2606 tp->prior_cwnd = tcp_snd_cwnd(tp);
2607 tp->prr_delivered = 0;
2609 tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
2610 tcp_ecn_queue_cwr(tp);
2613 void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int newly_lost, int flag)
2615 struct tcp_sock *tp = tcp_sk(sk);
2617 int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2619 if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
2622 tp->prr_delivered += newly_acked_sacked;
2624 u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2626 sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
2628 sndcnt = max_t(int, tp->prr_delivered - tp->prr_out,
2629 newly_acked_sacked);
2630 if (flag & FLAG_SND_UNA_ADVANCED && !newly_lost)
2632 sndcnt = min(delta, sndcnt);
2634 /* Force a fast retransmit upon entering fast recovery */
2635 sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
2636 tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + sndcnt);
2639 static inline void tcp_end_cwnd_reduction(struct sock *sk)
2641 struct tcp_sock *tp = tcp_sk(sk);
2643 if (inet_csk(sk)->icsk_ca_ops->cong_control)
2646 /* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
2647 if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
2648 (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) {
2649 tcp_snd_cwnd_set(tp, tp->snd_ssthresh);
2650 tp->snd_cwnd_stamp = tcp_jiffies32;
2652 tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2655 /* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
2656 void tcp_enter_cwr(struct sock *sk)
2658 struct tcp_sock *tp = tcp_sk(sk);
2660 tp->prior_ssthresh = 0;
2661 if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2662 tp->undo_marker = 0;
2663 tcp_init_cwnd_reduction(sk);
2664 tcp_set_ca_state(sk, TCP_CA_CWR);
2667 EXPORT_SYMBOL(tcp_enter_cwr);
2669 static void tcp_try_keep_open(struct sock *sk)
2671 struct tcp_sock *tp = tcp_sk(sk);
2672 int state = TCP_CA_Open;
2674 if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2675 state = TCP_CA_Disorder;
2677 if (inet_csk(sk)->icsk_ca_state != state) {
2678 tcp_set_ca_state(sk, state);
2679 tp->high_seq = tp->snd_nxt;
2683 static void tcp_try_to_open(struct sock *sk, int flag)
2685 struct tcp_sock *tp = tcp_sk(sk);
2687 tcp_verify_left_out(tp);
2689 if (!tcp_any_retrans_done(sk))
2690 tp->retrans_stamp = 0;
2692 if (flag & FLAG_ECE)
2695 if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2696 tcp_try_keep_open(sk);
2700 static void tcp_mtup_probe_failed(struct sock *sk)
2702 struct inet_connection_sock *icsk = inet_csk(sk);
2704 icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2705 icsk->icsk_mtup.probe_size = 0;
2706 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
2709 static void tcp_mtup_probe_success(struct sock *sk)
2711 struct tcp_sock *tp = tcp_sk(sk);
2712 struct inet_connection_sock *icsk = inet_csk(sk);
2715 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2717 val = (u64)tcp_snd_cwnd(tp) * tcp_mss_to_mtu(sk, tp->mss_cache);
2718 do_div(val, icsk->icsk_mtup.probe_size);
2719 DEBUG_NET_WARN_ON_ONCE((u32)val != val);
2720 tcp_snd_cwnd_set(tp, max_t(u32, 1U, val));
2722 tp->snd_cwnd_cnt = 0;
2723 tp->snd_cwnd_stamp = tcp_jiffies32;
2724 tp->snd_ssthresh = tcp_current_ssthresh(sk);
2726 icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2727 icsk->icsk_mtup.probe_size = 0;
2728 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2729 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
2732 /* Do a simple retransmit without using the backoff mechanisms in
2733 * tcp_timer. This is used for path mtu discovery.
2734 * The socket is already locked here.
2736 void tcp_simple_retransmit(struct sock *sk)
2738 const struct inet_connection_sock *icsk = inet_csk(sk);
2739 struct tcp_sock *tp = tcp_sk(sk);
2740 struct sk_buff *skb;
2743 /* A fastopen SYN request is stored as two separate packets within
2744 * the retransmit queue, this is done by tcp_send_syn_data().
2745 * As a result simply checking the MSS of the frames in the queue
2746 * will not work for the SYN packet.
2748 * Us being here is an indication of a path MTU issue so we can
2749 * assume that the fastopen SYN was lost and just mark all the
2750 * frames in the retransmit queue as lost. We will use an MSS of
2751 * -1 to mark all frames as lost, otherwise compute the current MSS.
2753 if (tp->syn_data && sk->sk_state == TCP_SYN_SENT)
2756 mss = tcp_current_mss(sk);
2758 skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2759 if (tcp_skb_seglen(skb) > mss)
2760 tcp_mark_skb_lost(sk, skb);
2763 tcp_clear_retrans_hints_partial(tp);
2768 if (tcp_is_reno(tp))
2769 tcp_limit_reno_sacked(tp);
2771 tcp_verify_left_out(tp);
2773 /* Don't muck with the congestion window here.
2774 * Reason is that we do not increase amount of _data_
2775 * in network, but units changed and effective
2776 * cwnd/ssthresh really reduced now.
2778 if (icsk->icsk_ca_state != TCP_CA_Loss) {
2779 tp->high_seq = tp->snd_nxt;
2780 tp->snd_ssthresh = tcp_current_ssthresh(sk);
2781 tp->prior_ssthresh = 0;
2782 tp->undo_marker = 0;
2783 tcp_set_ca_state(sk, TCP_CA_Loss);
2785 tcp_xmit_retransmit_queue(sk);
2787 EXPORT_SYMBOL(tcp_simple_retransmit);
2789 void tcp_enter_recovery(struct sock *sk, bool ece_ack)
2791 struct tcp_sock *tp = tcp_sk(sk);
2794 if (tcp_is_reno(tp))
2795 mib_idx = LINUX_MIB_TCPRENORECOVERY;
2797 mib_idx = LINUX_MIB_TCPSACKRECOVERY;
2799 NET_INC_STATS(sock_net(sk), mib_idx);
2801 tp->prior_ssthresh = 0;
2804 if (!tcp_in_cwnd_reduction(sk)) {
2806 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2807 tcp_init_cwnd_reduction(sk);
2809 tcp_set_ca_state(sk, TCP_CA_Recovery);
2812 /* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
2813 * recovered or spurious. Otherwise retransmits more on partial ACKs.
2815 static void tcp_process_loss(struct sock *sk, int flag, int num_dupack,
2818 struct tcp_sock *tp = tcp_sk(sk);
2819 bool recovered = !before(tp->snd_una, tp->high_seq);
2821 if ((flag & FLAG_SND_UNA_ADVANCED || rcu_access_pointer(tp->fastopen_rsk)) &&
2822 tcp_try_undo_loss(sk, false))
2825 if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
2826 /* Step 3.b. A timeout is spurious if not all data are
2827 * lost, i.e., never-retransmitted data are (s)acked.
2829 if ((flag & FLAG_ORIG_SACK_ACKED) &&
2830 tcp_try_undo_loss(sk, true))
2833 if (after(tp->snd_nxt, tp->high_seq)) {
2834 if (flag & FLAG_DATA_SACKED || num_dupack)
2835 tp->frto = 0; /* Step 3.a. loss was real */
2836 } else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
2837 tp->high_seq = tp->snd_nxt;
2838 /* Step 2.b. Try send new data (but deferred until cwnd
2839 * is updated in tcp_ack()). Otherwise fall back to
2840 * the conventional recovery.
2842 if (!tcp_write_queue_empty(sk) &&
2843 after(tcp_wnd_end(tp), tp->snd_nxt)) {
2844 *rexmit = REXMIT_NEW;
2852 /* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
2853 tcp_try_undo_recovery(sk);
2856 if (tcp_is_reno(tp)) {
2857 /* A Reno DUPACK means new data in F-RTO step 2.b above are
2858 * delivered. Lower inflight to clock out (re)tranmissions.
2860 if (after(tp->snd_nxt, tp->high_seq) && num_dupack)
2861 tcp_add_reno_sack(sk, num_dupack, flag & FLAG_ECE);
2862 else if (flag & FLAG_SND_UNA_ADVANCED)
2863 tcp_reset_reno_sack(tp);
2865 *rexmit = REXMIT_LOST;
2868 static bool tcp_force_fast_retransmit(struct sock *sk)
2870 struct tcp_sock *tp = tcp_sk(sk);
2872 return after(tcp_highest_sack_seq(tp),
2873 tp->snd_una + tp->reordering * tp->mss_cache);
2876 /* Undo during fast recovery after partial ACK. */
2877 static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una,
2880 struct tcp_sock *tp = tcp_sk(sk);
2882 if (tp->undo_marker && tcp_packet_delayed(tp)) {
2883 /* Plain luck! Hole if filled with delayed
2884 * packet, rather than with a retransmit. Check reordering.
2886 tcp_check_sack_reordering(sk, prior_snd_una, 1);
2888 /* We are getting evidence that the reordering degree is higher
2889 * than we realized. If there are no retransmits out then we
2890 * can undo. Otherwise we clock out new packets but do not
2891 * mark more packets lost or retransmit more.
2893 if (tp->retrans_out)
2896 if (!tcp_any_retrans_done(sk))
2897 tp->retrans_stamp = 0;
2899 DBGUNDO(sk, "partial recovery");
2900 tcp_undo_cwnd_reduction(sk, true);
2901 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2902 tcp_try_keep_open(sk);
2904 /* Partial ACK arrived. Force fast retransmit. */
2905 *do_lost = tcp_force_fast_retransmit(sk);
2910 static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag)
2912 struct tcp_sock *tp = tcp_sk(sk);
2914 if (tcp_rtx_queue_empty(sk))
2917 if (unlikely(tcp_is_reno(tp))) {
2918 tcp_newreno_mark_lost(sk, *ack_flag & FLAG_SND_UNA_ADVANCED);
2919 } else if (tcp_is_rack(sk)) {
2920 u32 prior_retrans = tp->retrans_out;
2922 if (tcp_rack_mark_lost(sk))
2923 *ack_flag &= ~FLAG_SET_XMIT_TIMER;
2924 if (prior_retrans > tp->retrans_out)
2925 *ack_flag |= FLAG_LOST_RETRANS;
2929 /* Process an event, which can update packets-in-flight not trivially.
2930 * Main goal of this function is to calculate new estimate for left_out,
2931 * taking into account both packets sitting in receiver's buffer and
2932 * packets lost by network.
2934 * Besides that it updates the congestion state when packet loss or ECN
2935 * is detected. But it does not reduce the cwnd, it is done by the
2936 * congestion control later.
2938 * It does _not_ decide what to send, it is made in function
2939 * tcp_xmit_retransmit_queue().
2941 static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
2942 int num_dupack, int *ack_flag, int *rexmit)
2944 struct inet_connection_sock *icsk = inet_csk(sk);
2945 struct tcp_sock *tp = tcp_sk(sk);
2946 int fast_rexmit = 0, flag = *ack_flag;
2947 bool ece_ack = flag & FLAG_ECE;
2948 bool do_lost = num_dupack || ((flag & FLAG_DATA_SACKED) &&
2949 tcp_force_fast_retransmit(sk));
2951 if (!tp->packets_out && tp->sacked_out)
2954 /* Now state machine starts.
2955 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2957 tp->prior_ssthresh = 0;
2959 /* B. In all the states check for reneging SACKs. */
2960 if (tcp_check_sack_reneging(sk, flag))
2963 /* C. Check consistency of the current state. */
2964 tcp_verify_left_out(tp);
2966 /* D. Check state exit conditions. State can be terminated
2967 * when high_seq is ACKed. */
2968 if (icsk->icsk_ca_state == TCP_CA_Open) {
2969 WARN_ON(tp->retrans_out != 0 && !tp->syn_data);
2970 tp->retrans_stamp = 0;
2971 } else if (!before(tp->snd_una, tp->high_seq)) {
2972 switch (icsk->icsk_ca_state) {
2974 /* CWR is to be held something *above* high_seq
2975 * is ACKed for CWR bit to reach receiver. */
2976 if (tp->snd_una != tp->high_seq) {
2977 tcp_end_cwnd_reduction(sk);
2978 tcp_set_ca_state(sk, TCP_CA_Open);
2982 case TCP_CA_Recovery:
2983 if (tcp_is_reno(tp))
2984 tcp_reset_reno_sack(tp);
2985 if (tcp_try_undo_recovery(sk))
2987 tcp_end_cwnd_reduction(sk);
2992 /* E. Process state. */
2993 switch (icsk->icsk_ca_state) {
2994 case TCP_CA_Recovery:
2995 if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2996 if (tcp_is_reno(tp))
2997 tcp_add_reno_sack(sk, num_dupack, ece_ack);
2998 } else if (tcp_try_undo_partial(sk, prior_snd_una, &do_lost))
3001 if (tcp_try_undo_dsack(sk))
3002 tcp_try_keep_open(sk);
3004 tcp_identify_packet_loss(sk, ack_flag);
3005 if (icsk->icsk_ca_state != TCP_CA_Recovery) {
3006 if (!tcp_time_to_recover(sk, flag))
3008 /* Undo reverts the recovery state. If loss is evident,
3009 * starts a new recovery (e.g. reordering then loss);
3011 tcp_enter_recovery(sk, ece_ack);
3015 tcp_process_loss(sk, flag, num_dupack, rexmit);
3016 tcp_identify_packet_loss(sk, ack_flag);
3017 if (!(icsk->icsk_ca_state == TCP_CA_Open ||
3018 (*ack_flag & FLAG_LOST_RETRANS)))
3020 /* Change state if cwnd is undone or retransmits are lost */
3023 if (tcp_is_reno(tp)) {
3024 if (flag & FLAG_SND_UNA_ADVANCED)
3025 tcp_reset_reno_sack(tp);
3026 tcp_add_reno_sack(sk, num_dupack, ece_ack);
3029 if (icsk->icsk_ca_state <= TCP_CA_Disorder)
3030 tcp_try_undo_dsack(sk);
3032 tcp_identify_packet_loss(sk, ack_flag);
3033 if (!tcp_time_to_recover(sk, flag)) {
3034 tcp_try_to_open(sk, flag);
3038 /* MTU probe failure: don't reduce cwnd */
3039 if (icsk->icsk_ca_state < TCP_CA_CWR &&
3040 icsk->icsk_mtup.probe_size &&
3041 tp->snd_una == tp->mtu_probe.probe_seq_start) {
3042 tcp_mtup_probe_failed(sk);
3043 /* Restores the reduction we did in tcp_mtup_probe() */
3044 tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
3045 tcp_simple_retransmit(sk);
3049 /* Otherwise enter Recovery state */
3050 tcp_enter_recovery(sk, ece_ack);
3054 if (!tcp_is_rack(sk) && do_lost)
3055 tcp_update_scoreboard(sk, fast_rexmit);
3056 *rexmit = REXMIT_LOST;
3059 static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us, const int flag)
3061 u32 wlen = sock_net(sk)->ipv4.sysctl_tcp_min_rtt_wlen * HZ;
3062 struct tcp_sock *tp = tcp_sk(sk);
3064 if ((flag & FLAG_ACK_MAYBE_DELAYED) && rtt_us > tcp_min_rtt(tp)) {
3065 /* If the remote keeps returning delayed ACKs, eventually
3066 * the min filter would pick it up and overestimate the
3067 * prop. delay when it expires. Skip suspected delayed ACKs.
3071 minmax_running_min(&tp->rtt_min, wlen, tcp_jiffies32,
3072 rtt_us ? : jiffies_to_usecs(1));
3075 static bool tcp_ack_update_rtt(struct sock *sk, const int flag,
3076 long seq_rtt_us, long sack_rtt_us,
3077 long ca_rtt_us, struct rate_sample *rs)
3079 const struct tcp_sock *tp = tcp_sk(sk);
3081 /* Prefer RTT measured from ACK's timing to TS-ECR. This is because
3082 * broken middle-boxes or peers may corrupt TS-ECR fields. But
3083 * Karn's algorithm forbids taking RTT if some retransmitted data
3084 * is acked (RFC6298).
3087 seq_rtt_us = sack_rtt_us;
3089 /* RTTM Rule: A TSecr value received in a segment is used to
3090 * update the averaged RTT measurement only if the segment
3091 * acknowledges some new data, i.e., only if it advances the
3092 * left edge of the send window.
3093 * See draft-ietf-tcplw-high-performance-00, section 3.3.
3095 if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
3096 flag & FLAG_ACKED) {
3097 u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
3099 if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
3102 seq_rtt_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
3103 ca_rtt_us = seq_rtt_us;
3106 rs->rtt_us = ca_rtt_us; /* RTT of last (S)ACKed packet (or -1) */
3110 /* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is
3111 * always taken together with ACK, SACK, or TS-opts. Any negative
3112 * values will be skipped with the seq_rtt_us < 0 check above.
3114 tcp_update_rtt_min(sk, ca_rtt_us, flag);
3115 tcp_rtt_estimator(sk, seq_rtt_us);
3118 /* RFC6298: only reset backoff on valid RTT measurement. */
3119 inet_csk(sk)->icsk_backoff = 0;
3123 /* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
3124 void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
3126 struct rate_sample rs;
3129 if (req && !req->num_retrans && tcp_rsk(req)->snt_synack)
3130 rtt_us = tcp_stamp_us_delta(tcp_clock_us(), tcp_rsk(req)->snt_synack);
3132 tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us, &rs);
3136 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
3138 const struct inet_connection_sock *icsk = inet_csk(sk);
3140 icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
3141 tcp_sk(sk)->snd_cwnd_stamp = tcp_jiffies32;
3144 /* Restart timer after forward progress on connection.
3145 * RFC2988 recommends to restart timer to now+rto.
3147 void tcp_rearm_rto(struct sock *sk)
3149 const struct inet_connection_sock *icsk = inet_csk(sk);
3150 struct tcp_sock *tp = tcp_sk(sk);
3152 /* If the retrans timer is currently being used by Fast Open
3153 * for SYN-ACK retrans purpose, stay put.
3155 if (rcu_access_pointer(tp->fastopen_rsk))
3158 if (!tp->packets_out) {
3159 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3161 u32 rto = inet_csk(sk)->icsk_rto;
3162 /* Offset the time elapsed after installing regular RTO */
3163 if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
3164 icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
3165 s64 delta_us = tcp_rto_delta_us(sk);
3166 /* delta_us may not be positive if the socket is locked
3167 * when the retrans timer fires and is rescheduled.
3169 rto = usecs_to_jiffies(max_t(int, delta_us, 1));
3171 tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
3176 /* Try to schedule a loss probe; if that doesn't work, then schedule an RTO. */
3177 static void tcp_set_xmit_timer(struct sock *sk)
3179 if (!tcp_schedule_loss_probe(sk, true))
3183 /* If we get here, the whole TSO packet has not been acked. */
3184 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3186 struct tcp_sock *tp = tcp_sk(sk);
3189 BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3191 packets_acked = tcp_skb_pcount(skb);
3192 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3194 packets_acked -= tcp_skb_pcount(skb);
3196 if (packets_acked) {
3197 BUG_ON(tcp_skb_pcount(skb) == 0);
3198 BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3201 return packets_acked;
3204 static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
3205 const struct sk_buff *ack_skb, u32 prior_snd_una)
3207 const struct skb_shared_info *shinfo;
3209 /* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
3210 if (likely(!TCP_SKB_CB(skb)->txstamp_ack))
3213 shinfo = skb_shinfo(skb);
3214 if (!before(shinfo->tskey, prior_snd_una) &&
3215 before(shinfo->tskey, tcp_sk(sk)->snd_una)) {
3216 tcp_skb_tsorted_save(skb) {
3217 __skb_tstamp_tx(skb, ack_skb, NULL, sk, SCM_TSTAMP_ACK);
3218 } tcp_skb_tsorted_restore(skb);
3222 /* Remove acknowledged frames from the retransmission queue. If our packet
3223 * is before the ack sequence we can discard it as it's confirmed to have
3224 * arrived at the other end.
3226 static int tcp_clean_rtx_queue(struct sock *sk, const struct sk_buff *ack_skb,
3227 u32 prior_fack, u32 prior_snd_una,
3228 struct tcp_sacktag_state *sack, bool ece_ack)
3230 const struct inet_connection_sock *icsk = inet_csk(sk);
3231 u64 first_ackt, last_ackt;
3232 struct tcp_sock *tp = tcp_sk(sk);
3233 u32 prior_sacked = tp->sacked_out;
3234 u32 reord = tp->snd_nxt; /* lowest acked un-retx un-sacked seq */
3235 struct sk_buff *skb, *next;
3236 bool fully_acked = true;
3237 long sack_rtt_us = -1L;
3238 long seq_rtt_us = -1L;
3239 long ca_rtt_us = -1L;
3246 for (skb = skb_rb_first(&sk->tcp_rtx_queue); skb; skb = next) {
3247 struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3248 const u32 start_seq = scb->seq;
3249 u8 sacked = scb->sacked;
3252 /* Determine how many packets and what bytes were acked, tso and else */
3253 if (after(scb->end_seq, tp->snd_una)) {
3254 if (tcp_skb_pcount(skb) == 1 ||
3255 !after(tp->snd_una, scb->seq))
3258 acked_pcount = tcp_tso_acked(sk, skb);
3261 fully_acked = false;
3263 acked_pcount = tcp_skb_pcount(skb);
3266 if (unlikely(sacked & TCPCB_RETRANS)) {
3267 if (sacked & TCPCB_SACKED_RETRANS)
3268 tp->retrans_out -= acked_pcount;
3269 flag |= FLAG_RETRANS_DATA_ACKED;
3270 } else if (!(sacked & TCPCB_SACKED_ACKED)) {
3271 last_ackt = tcp_skb_timestamp_us(skb);
3272 WARN_ON_ONCE(last_ackt == 0);
3274 first_ackt = last_ackt;
3276 if (before(start_seq, reord))
3278 if (!after(scb->end_seq, tp->high_seq))
3279 flag |= FLAG_ORIG_SACK_ACKED;
3282 if (sacked & TCPCB_SACKED_ACKED) {
3283 tp->sacked_out -= acked_pcount;
3284 } else if (tcp_is_sack(tp)) {
3285 tcp_count_delivered(tp, acked_pcount, ece_ack);
3286 if (!tcp_skb_spurious_retrans(tp, skb))
3287 tcp_rack_advance(tp, sacked, scb->end_seq,
3288 tcp_skb_timestamp_us(skb));
3290 if (sacked & TCPCB_LOST)
3291 tp->lost_out -= acked_pcount;
3293 tp->packets_out -= acked_pcount;
3294 pkts_acked += acked_pcount;
3295 tcp_rate_skb_delivered(sk, skb, sack->rate);
3297 /* Initial outgoing SYN's get put onto the write_queue
3298 * just like anything else we transmit. It is not
3299 * true data, and if we misinform our callers that
3300 * this ACK acks real data, we will erroneously exit
3301 * connection startup slow start one packet too
3302 * quickly. This is severely frowned upon behavior.
3304 if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
3305 flag |= FLAG_DATA_ACKED;
3307 flag |= FLAG_SYN_ACKED;
3308 tp->retrans_stamp = 0;
3314 tcp_ack_tstamp(sk, skb, ack_skb, prior_snd_una);
3316 next = skb_rb_next(skb);
3317 if (unlikely(skb == tp->retransmit_skb_hint))
3318 tp->retransmit_skb_hint = NULL;
3319 if (unlikely(skb == tp->lost_skb_hint))
3320 tp->lost_skb_hint = NULL;
3321 tcp_highest_sack_replace(sk, skb, next);
3322 tcp_rtx_queue_unlink_and_free(skb, sk);
3326 tcp_chrono_stop(sk, TCP_CHRONO_BUSY);
3328 if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3329 tp->snd_up = tp->snd_una;
3332 tcp_ack_tstamp(sk, skb, ack_skb, prior_snd_una);
3333 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
3334 flag |= FLAG_SACK_RENEGING;
3337 if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
3338 seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt);
3339 ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt);
3341 if (pkts_acked == 1 && fully_acked && !prior_sacked &&
3342 (tp->snd_una - prior_snd_una) < tp->mss_cache &&
3343 sack->rate->prior_delivered + 1 == tp->delivered &&
3344 !(flag & (FLAG_CA_ALERT | FLAG_SYN_ACKED))) {
3345 /* Conservatively mark a delayed ACK. It's typically
3346 * from a lone runt packet over the round trip to
3347 * a receiver w/o out-of-order or CE events.
3349 flag |= FLAG_ACK_MAYBE_DELAYED;
3352 if (sack->first_sackt) {
3353 sack_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->first_sackt);
3354 ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->last_sackt);
3356 rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
3357 ca_rtt_us, sack->rate);
3359 if (flag & FLAG_ACKED) {
3360 flag |= FLAG_SET_XMIT_TIMER; /* set TLP or RTO timer */
3361 if (unlikely(icsk->icsk_mtup.probe_size &&
3362 !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3363 tcp_mtup_probe_success(sk);
3366 if (tcp_is_reno(tp)) {
3367 tcp_remove_reno_sacks(sk, pkts_acked, ece_ack);
3369 /* If any of the cumulatively ACKed segments was
3370 * retransmitted, non-SACK case cannot confirm that
3371 * progress was due to original transmission due to
3372 * lack of TCPCB_SACKED_ACKED bits even if some of
3373 * the packets may have been never retransmitted.
3375 if (flag & FLAG_RETRANS_DATA_ACKED)
3376 flag &= ~FLAG_ORIG_SACK_ACKED;
3380 /* Non-retransmitted hole got filled? That's reordering */
3381 if (before(reord, prior_fack))
3382 tcp_check_sack_reordering(sk, reord, 0);
3384 delta = prior_sacked - tp->sacked_out;
3385 tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3387 } else if (skb && rtt_update && sack_rtt_us >= 0 &&
3388 sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp,
3389 tcp_skb_timestamp_us(skb))) {
3390 /* Do not re-arm RTO if the sack RTT is measured from data sent
3391 * after when the head was last (re)transmitted. Otherwise the
3392 * timeout may continue to extend in loss recovery.
3394 flag |= FLAG_SET_XMIT_TIMER; /* set TLP or RTO timer */
3397 if (icsk->icsk_ca_ops->pkts_acked) {
3398 struct ack_sample sample = { .pkts_acked = pkts_acked,
3399 .rtt_us = sack->rate->rtt_us };
3401 sample.in_flight = tp->mss_cache *
3402 (tp->delivered - sack->rate->prior_delivered);
3403 icsk->icsk_ca_ops->pkts_acked(sk, &sample);
3406 #if FASTRETRANS_DEBUG > 0
3407 WARN_ON((int)tp->sacked_out < 0);
3408 WARN_ON((int)tp->lost_out < 0);
3409 WARN_ON((int)tp->retrans_out < 0);
3410 if (!tp->packets_out && tcp_is_sack(tp)) {
3411 icsk = inet_csk(sk);
3413 pr_debug("Leak l=%u %d\n",
3414 tp->lost_out, icsk->icsk_ca_state);
3417 if (tp->sacked_out) {
3418 pr_debug("Leak s=%u %d\n",
3419 tp->sacked_out, icsk->icsk_ca_state);
3422 if (tp->retrans_out) {
3423 pr_debug("Leak r=%u %d\n",
3424 tp->retrans_out, icsk->icsk_ca_state);
3425 tp->retrans_out = 0;
3432 static void tcp_ack_probe(struct sock *sk)
3434 struct inet_connection_sock *icsk = inet_csk(sk);
3435 struct sk_buff *head = tcp_send_head(sk);
3436 const struct tcp_sock *tp = tcp_sk(sk);
3438 /* Was it a usable window open? */
3441 if (!after(TCP_SKB_CB(head)->end_seq, tcp_wnd_end(tp))) {
3442 icsk->icsk_backoff = 0;
3443 icsk->icsk_probes_tstamp = 0;
3444 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3445 /* Socket must be waked up by subsequent tcp_data_snd_check().
3446 * This function is not for random using!
3449 unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);
3451 when = tcp_clamp_probe0_to_user_timeout(sk, when);
3452 tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0, when, TCP_RTO_MAX);
3456 static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
3458 return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3459 inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3462 /* Decide wheather to run the increase function of congestion control. */
3463 static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3465 /* If reordering is high then always grow cwnd whenever data is
3466 * delivered regardless of its ordering. Otherwise stay conservative
3467 * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
3468 * new SACK or ECE mark may first advance cwnd here and later reduce
3469 * cwnd in tcp_fastretrans_alert() based on more states.
3471 if (tcp_sk(sk)->reordering >
3472 READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_reordering))
3473 return flag & FLAG_FORWARD_PROGRESS;
3475 return flag & FLAG_DATA_ACKED;
3478 /* The "ultimate" congestion control function that aims to replace the rigid
3479 * cwnd increase and decrease control (tcp_cong_avoid,tcp_*cwnd_reduction).
3480 * It's called toward the end of processing an ACK with precise rate
3481 * information. All transmission or retransmission are delayed afterwards.
3483 static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
3484 int flag, const struct rate_sample *rs)
3486 const struct inet_connection_sock *icsk = inet_csk(sk);
3488 if (icsk->icsk_ca_ops->cong_control) {
3489 icsk->icsk_ca_ops->cong_control(sk, rs);
3493 if (tcp_in_cwnd_reduction(sk)) {
3494 /* Reduce cwnd if state mandates */
3495 tcp_cwnd_reduction(sk, acked_sacked, rs->losses, flag);
3496 } else if (tcp_may_raise_cwnd(sk, flag)) {
3497 /* Advance cwnd if state allows */
3498 tcp_cong_avoid(sk, ack, acked_sacked);
3500 tcp_update_pacing_rate(sk);
3503 /* Check that window update is acceptable.
3504 * The function assumes that snd_una<=ack<=snd_next.
3506 static inline bool tcp_may_update_window(const struct tcp_sock *tp,
3507 const u32 ack, const u32 ack_seq,
3510 return after(ack, tp->snd_una) ||
3511 after(ack_seq, tp->snd_wl1) ||
3512 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
3515 /* If we update tp->snd_una, also update tp->bytes_acked */
3516 static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
3518 u32 delta = ack - tp->snd_una;
3520 sock_owned_by_me((struct sock *)tp);
3521 tp->bytes_acked += delta;
3525 /* If we update tp->rcv_nxt, also update tp->bytes_received */
3526 static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
3528 u32 delta = seq - tp->rcv_nxt;
3530 sock_owned_by_me((struct sock *)tp);
3531 tp->bytes_received += delta;
3532 WRITE_ONCE(tp->rcv_nxt, seq);
3535 /* Update our send window.
3537 * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3538 * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3540 static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3543 struct tcp_sock *tp = tcp_sk(sk);
3545 u32 nwin = ntohs(tcp_hdr(skb)->window);
3547 if (likely(!tcp_hdr(skb)->syn))
3548 nwin <<= tp->rx_opt.snd_wscale;
3550 if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3551 flag |= FLAG_WIN_UPDATE;
3552 tcp_update_wl(tp, ack_seq);
3554 if (tp->snd_wnd != nwin) {
3557 /* Note, it is the only place, where
3558 * fast path is recovered for sending TCP.
3561 tcp_fast_path_check(sk);
3563 if (!tcp_write_queue_empty(sk))
3564 tcp_slow_start_after_idle_check(sk);
3566 if (nwin > tp->max_window) {
3567 tp->max_window = nwin;
3568 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3573 tcp_snd_una_update(tp, ack);
3578 static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
3579 u32 *last_oow_ack_time)
3581 if (*last_oow_ack_time) {
3582 s32 elapsed = (s32)(tcp_jiffies32 - *last_oow_ack_time);
3584 if (0 <= elapsed && elapsed < net->ipv4.sysctl_tcp_invalid_ratelimit) {
3585 NET_INC_STATS(net, mib_idx);
3586 return true; /* rate-limited: don't send yet! */
3590 *last_oow_ack_time = tcp_jiffies32;
3592 return false; /* not rate-limited: go ahead, send dupack now! */
3595 /* Return true if we're currently rate-limiting out-of-window ACKs and
3596 * thus shouldn't send a dupack right now. We rate-limit dupacks in
3597 * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
3598 * attacks that send repeated SYNs or ACKs for the same connection. To
3599 * do this, we do not send a duplicate SYNACK or ACK if the remote
3600 * endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
3602 bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
3603 int mib_idx, u32 *last_oow_ack_time)
3605 /* Data packets without SYNs are not likely part of an ACK loop. */
3606 if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
3610 return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time);
3613 /* RFC 5961 7 [ACK Throttling] */
3614 static void tcp_send_challenge_ack(struct sock *sk)
3616 /* unprotected vars, we dont care of overwrites */
3617 static u32 challenge_timestamp;
3618 static unsigned int challenge_count;
3619 struct tcp_sock *tp = tcp_sk(sk);
3620 struct net *net = sock_net(sk);
3623 /* First check our per-socket dupack rate limit. */
3624 if (__tcp_oow_rate_limited(net,
3625 LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
3626 &tp->last_oow_ack_time))
3629 /* Then check host-wide RFC 5961 rate limit. */
3631 if (now != challenge_timestamp) {
3632 u32 ack_limit = net->ipv4.sysctl_tcp_challenge_ack_limit;
3633 u32 half = (ack_limit + 1) >> 1;
3635 challenge_timestamp = now;
3636 WRITE_ONCE(challenge_count, half + prandom_u32_max(ack_limit));
3638 count = READ_ONCE(challenge_count);
3640 WRITE_ONCE(challenge_count, count - 1);
3641 NET_INC_STATS(net, LINUX_MIB_TCPCHALLENGEACK);
3646 static void tcp_store_ts_recent(struct tcp_sock *tp)
3648 tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3649 tp->rx_opt.ts_recent_stamp = ktime_get_seconds();
3652 static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3654 if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3655 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
3656 * extra check below makes sure this can only happen
3657 * for pure ACK frames. -DaveM
3659 * Not only, also it occurs for expired timestamps.
3662 if (tcp_paws_check(&tp->rx_opt, 0))
3663 tcp_store_ts_recent(tp);
3667 /* This routine deals with acks during a TLP episode and ends an episode by
3668 * resetting tlp_high_seq. Ref: TLP algorithm in draft-ietf-tcpm-rack
3670 static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
3672 struct tcp_sock *tp = tcp_sk(sk);
3674 if (before(ack, tp->tlp_high_seq))
3677 if (!tp->tlp_retrans) {
3678 /* TLP of new data has been acknowledged */
3679 tp->tlp_high_seq = 0;
3680 } else if (flag & FLAG_DSACK_TLP) {
3681 /* This DSACK means original and TLP probe arrived; no loss */
3682 tp->tlp_high_seq = 0;
3683 } else if (after(ack, tp->tlp_high_seq)) {
3684 /* ACK advances: there was a loss, so reduce cwnd. Reset
3685 * tlp_high_seq in tcp_init_cwnd_reduction()
3687 tcp_init_cwnd_reduction(sk);
3688 tcp_set_ca_state(sk, TCP_CA_CWR);
3689 tcp_end_cwnd_reduction(sk);
3690 tcp_try_keep_open(sk);
3691 NET_INC_STATS(sock_net(sk),
3692 LINUX_MIB_TCPLOSSPROBERECOVERY);
3693 } else if (!(flag & (FLAG_SND_UNA_ADVANCED |
3694 FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
3695 /* Pure dupack: original and TLP probe arrived; no loss */
3696 tp->tlp_high_seq = 0;
3700 static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
3702 const struct inet_connection_sock *icsk = inet_csk(sk);
3704 if (icsk->icsk_ca_ops->in_ack_event)
3705 icsk->icsk_ca_ops->in_ack_event(sk, flags);
3708 /* Congestion control has updated the cwnd already. So if we're in
3709 * loss recovery then now we do any new sends (for FRTO) or
3710 * retransmits (for CA_Loss or CA_recovery) that make sense.
3712 static void tcp_xmit_recovery(struct sock *sk, int rexmit)
3714 struct tcp_sock *tp = tcp_sk(sk);
3716 if (rexmit == REXMIT_NONE || sk->sk_state == TCP_SYN_SENT)
3719 if (unlikely(rexmit == REXMIT_NEW)) {
3720 __tcp_push_pending_frames(sk, tcp_current_mss(sk),
3722 if (after(tp->snd_nxt, tp->high_seq))
3726 tcp_xmit_retransmit_queue(sk);
3729 /* Returns the number of packets newly acked or sacked by the current ACK */
3730 static u32 tcp_newly_delivered(struct sock *sk, u32 prior_delivered, int flag)
3732 const struct net *net = sock_net(sk);
3733 struct tcp_sock *tp = tcp_sk(sk);
3736 delivered = tp->delivered - prior_delivered;
3737 NET_ADD_STATS(net, LINUX_MIB_TCPDELIVERED, delivered);
3738 if (flag & FLAG_ECE)
3739 NET_ADD_STATS(net, LINUX_MIB_TCPDELIVEREDCE, delivered);
3744 /* This routine deals with incoming acks, but not outgoing ones. */
3745 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3747 struct inet_connection_sock *icsk = inet_csk(sk);
3748 struct tcp_sock *tp = tcp_sk(sk);
3749 struct tcp_sacktag_state sack_state;
3750 struct rate_sample rs = { .prior_delivered = 0 };
3751 u32 prior_snd_una = tp->snd_una;
3752 bool is_sack_reneg = tp->is_sack_reneg;
3753 u32 ack_seq = TCP_SKB_CB(skb)->seq;
3754 u32 ack = TCP_SKB_CB(skb)->ack_seq;
3756 int prior_packets = tp->packets_out;
3757 u32 delivered = tp->delivered;
3758 u32 lost = tp->lost;
3759 int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
3762 sack_state.first_sackt = 0;
3763 sack_state.rate = &rs;
3764 sack_state.sack_delivered = 0;
3766 /* We very likely will need to access rtx queue. */
3767 prefetch(sk->tcp_rtx_queue.rb_node);
3769 /* If the ack is older than previous acks
3770 * then we can probably ignore it.
3772 if (before(ack, prior_snd_una)) {
3773 /* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
3774 if (before(ack, prior_snd_una - tp->max_window)) {
3775 if (!(flag & FLAG_NO_CHALLENGE_ACK))
3776 tcp_send_challenge_ack(sk);
3777 return -SKB_DROP_REASON_TCP_TOO_OLD_ACK;
3782 /* If the ack includes data we haven't sent yet, discard
3783 * this segment (RFC793 Section 3.9).
3785 if (after(ack, tp->snd_nxt))
3786 return -SKB_DROP_REASON_TCP_ACK_UNSENT_DATA;
3788 if (after(ack, prior_snd_una)) {
3789 flag |= FLAG_SND_UNA_ADVANCED;
3790 icsk->icsk_retransmits = 0;
3792 #if IS_ENABLED(CONFIG_TLS_DEVICE)
3793 if (static_branch_unlikely(&clean_acked_data_enabled.key))
3794 if (icsk->icsk_clean_acked)
3795 icsk->icsk_clean_acked(sk, ack);
3799 prior_fack = tcp_is_sack(tp) ? tcp_highest_sack_seq(tp) : tp->snd_una;
3800 rs.prior_in_flight = tcp_packets_in_flight(tp);
3802 /* ts_recent update must be made after we are sure that the packet
3805 if (flag & FLAG_UPDATE_TS_RECENT)
3806 tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3808 if ((flag & (FLAG_SLOWPATH | FLAG_SND_UNA_ADVANCED)) ==
3809 FLAG_SND_UNA_ADVANCED) {
3810 /* Window is constant, pure forward advance.
3811 * No more checks are required.
3812 * Note, we use the fact that SND.UNA>=SND.WL2.
3814 tcp_update_wl(tp, ack_seq);
3815 tcp_snd_una_update(tp, ack);
3816 flag |= FLAG_WIN_UPDATE;
3818 tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);
3820 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS);
3822 u32 ack_ev_flags = CA_ACK_SLOWPATH;
3824 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3827 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3829 flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3831 if (TCP_SKB_CB(skb)->sacked)
3832 flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3835 if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) {
3837 ack_ev_flags |= CA_ACK_ECE;
3840 if (sack_state.sack_delivered)
3841 tcp_count_delivered(tp, sack_state.sack_delivered,
3844 if (flag & FLAG_WIN_UPDATE)
3845 ack_ev_flags |= CA_ACK_WIN_UPDATE;
3847 tcp_in_ack_event(sk, ack_ev_flags);
3850 /* This is a deviation from RFC3168 since it states that:
3851 * "When the TCP data sender is ready to set the CWR bit after reducing
3852 * the congestion window, it SHOULD set the CWR bit only on the first
3853 * new data packet that it transmits."
3854 * We accept CWR on pure ACKs to be more robust
3855 * with widely-deployed TCP implementations that do this.
3857 tcp_ecn_accept_cwr(sk, skb);
3859 /* We passed data and got it acked, remove any soft error
3860 * log. Something worked...
3862 sk->sk_err_soft = 0;
3863 icsk->icsk_probes_out = 0;
3864 tp->rcv_tstamp = tcp_jiffies32;
3868 /* See if we can take anything off of the retransmit queue. */
3869 flag |= tcp_clean_rtx_queue(sk, skb, prior_fack, prior_snd_una,
3870 &sack_state, flag & FLAG_ECE);
3872 tcp_rack_update_reo_wnd(sk, &rs);
3874 if (tp->tlp_high_seq)
3875 tcp_process_tlp_ack(sk, ack, flag);
3877 if (tcp_ack_is_dubious(sk, flag)) {
3878 if (!(flag & (FLAG_SND_UNA_ADVANCED |
3879 FLAG_NOT_DUP | FLAG_DSACKING_ACK))) {
3881 /* Consider if pure acks were aggregated in tcp_add_backlog() */
3882 if (!(flag & FLAG_DATA))
3883 num_dupack = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
3885 tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3889 /* If needed, reset TLP/RTO timer when RACK doesn't set. */
3890 if (flag & FLAG_SET_XMIT_TIMER)
3891 tcp_set_xmit_timer(sk);
3893 if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
3896 delivered = tcp_newly_delivered(sk, delivered, flag);
3897 lost = tp->lost - lost; /* freshly marked lost */
3898 rs.is_ack_delayed = !!(flag & FLAG_ACK_MAYBE_DELAYED);
3899 tcp_rate_gen(sk, delivered, lost, is_sack_reneg, sack_state.rate);
3900 tcp_cong_control(sk, ack, delivered, flag, sack_state.rate);
3901 tcp_xmit_recovery(sk, rexmit);
3905 /* If data was DSACKed, see if we can undo a cwnd reduction. */
3906 if (flag & FLAG_DSACKING_ACK) {
3907 tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3909 tcp_newly_delivered(sk, delivered, flag);
3911 /* If this ack opens up a zero window, clear backoff. It was
3912 * being used to time the probes, and is probably far higher than
3913 * it needs to be for normal retransmission.
3917 if (tp->tlp_high_seq)
3918 tcp_process_tlp_ack(sk, ack, flag);
3922 /* If data was SACKed, tag it and see if we should send more data.
3923 * If data was DSACKed, see if we can undo a cwnd reduction.
3925 if (TCP_SKB_CB(skb)->sacked) {
3926 flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3928 tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3930 tcp_newly_delivered(sk, delivered, flag);
3931 tcp_xmit_recovery(sk, rexmit);
3937 static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
3938 bool syn, struct tcp_fastopen_cookie *foc,
3941 /* Valid only in SYN or SYN-ACK with an even length. */
3942 if (!foc || !syn || len < 0 || (len & 1))
3945 if (len >= TCP_FASTOPEN_COOKIE_MIN &&
3946 len <= TCP_FASTOPEN_COOKIE_MAX)
3947 memcpy(foc->val, cookie, len);
3954 static bool smc_parse_options(const struct tcphdr *th,
3955 struct tcp_options_received *opt_rx,
3956 const unsigned char *ptr,
3959 #if IS_ENABLED(CONFIG_SMC)
3960 if (static_branch_unlikely(&tcp_have_smc)) {
3961 if (th->syn && !(opsize & 1) &&
3962 opsize >= TCPOLEN_EXP_SMC_BASE &&
3963 get_unaligned_be32(ptr) == TCPOPT_SMC_MAGIC) {
3972 /* Try to parse the MSS option from the TCP header. Return 0 on failure, clamped
3975 static u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss)
3977 const unsigned char *ptr = (const unsigned char *)(th + 1);
3978 int length = (th->doff * 4) - sizeof(struct tcphdr);
3981 while (length > 0) {
3982 int opcode = *ptr++;
3988 case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */
3995 if (opsize < 2) /* "silly options" */
3997 if (opsize > length)
3998 return mss; /* fail on partial options */
3999 if (opcode == TCPOPT_MSS && opsize == TCPOLEN_MSS) {
4000 u16 in_mss = get_unaligned_be16(ptr);
4003 if (user_mss && user_mss < in_mss)
4015 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
4016 * But, this can also be called on packets in the established flow when
4017 * the fast version below fails.
4019 void tcp_parse_options(const struct net *net,
4020 const struct sk_buff *skb,
4021 struct tcp_options_received *opt_rx, int estab,
4022 struct tcp_fastopen_cookie *foc)
4024 const unsigned char *ptr;
4025 const struct tcphdr *th = tcp_hdr(skb);
4026 int length = (th->doff * 4) - sizeof(struct tcphdr);
4028 ptr = (const unsigned char *)(th + 1);
4029 opt_rx->saw_tstamp = 0;
4030 opt_rx->saw_unknown = 0;
4032 while (length > 0) {
4033 int opcode = *ptr++;
4039 case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */
4046 if (opsize < 2) /* "silly options" */
4048 if (opsize > length)
4049 return; /* don't parse partial options */
4052 if (opsize == TCPOLEN_MSS && th->syn && !estab) {
4053 u16 in_mss = get_unaligned_be16(ptr);
4055 if (opt_rx->user_mss &&
4056 opt_rx->user_mss < in_mss)
4057 in_mss = opt_rx->user_mss;
4058 opt_rx->mss_clamp = in_mss;
4063 if (opsize == TCPOLEN_WINDOW && th->syn &&
4064 !estab && READ_ONCE(net->ipv4.sysctl_tcp_window_scaling)) {
4065 __u8 snd_wscale = *(__u8 *)ptr;
4066 opt_rx->wscale_ok = 1;
4067 if (snd_wscale > TCP_MAX_WSCALE) {
4068 net_info_ratelimited("%s: Illegal window scaling value %d > %u received\n",
4072 snd_wscale = TCP_MAX_WSCALE;
4074 opt_rx->snd_wscale = snd_wscale;
4077 case TCPOPT_TIMESTAMP:
4078 if ((opsize == TCPOLEN_TIMESTAMP) &&
4079 ((estab && opt_rx->tstamp_ok) ||
4080 (!estab && READ_ONCE(net->ipv4.sysctl_tcp_timestamps)))) {
4081 opt_rx->saw_tstamp = 1;
4082 opt_rx->rcv_tsval = get_unaligned_be32(ptr);
4083 opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
4086 case TCPOPT_SACK_PERM:
4087 if (opsize == TCPOLEN_SACK_PERM && th->syn &&
4088 !estab && READ_ONCE(net->ipv4.sysctl_tcp_sack)) {
4089 opt_rx->sack_ok = TCP_SACK_SEEN;
4090 tcp_sack_reset(opt_rx);
4095 if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
4096 !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
4098 TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
4101 #ifdef CONFIG_TCP_MD5SIG
4104 * The MD5 Hash has already been
4105 * checked (see tcp_v{4,6}_do_rcv()).
4109 case TCPOPT_FASTOPEN:
4110 tcp_parse_fastopen_option(
4111 opsize - TCPOLEN_FASTOPEN_BASE,
4112 ptr, th->syn, foc, false);
4116 /* Fast Open option shares code 254 using a
4117 * 16 bits magic number.
4119 if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
4120 get_unaligned_be16(ptr) ==
4121 TCPOPT_FASTOPEN_MAGIC) {
4122 tcp_parse_fastopen_option(opsize -
4123 TCPOLEN_EXP_FASTOPEN_BASE,
4124 ptr + 2, th->syn, foc, true);
4128 if (smc_parse_options(th, opt_rx, ptr, opsize))
4131 opt_rx->saw_unknown = 1;
4135 opt_rx->saw_unknown = 1;
4142 EXPORT_SYMBOL(tcp_parse_options);
4144 static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
4146 const __be32 *ptr = (const __be32 *)(th + 1);
4148 if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
4149 | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
4150 tp->rx_opt.saw_tstamp = 1;
4152 tp->rx_opt.rcv_tsval = ntohl(*ptr);
4155 tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
4157 tp->rx_opt.rcv_tsecr = 0;
4163 /* Fast parse options. This hopes to only see timestamps.
4164 * If it is wrong it falls back on tcp_parse_options().
4166 static bool tcp_fast_parse_options(const struct net *net,
4167 const struct sk_buff *skb,
4168 const struct tcphdr *th, struct tcp_sock *tp)
4170 /* In the spirit of fast parsing, compare doff directly to constant
4171 * values. Because equality is used, short doff can be ignored here.
4173 if (th->doff == (sizeof(*th) / 4)) {
4174 tp->rx_opt.saw_tstamp = 0;
4176 } else if (tp->rx_opt.tstamp_ok &&
4177 th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
4178 if (tcp_parse_aligned_timestamp(tp, th))
4182 tcp_parse_options(net, skb, &tp->rx_opt, 1, NULL);
4183 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
4184 tp->rx_opt.rcv_tsecr -= tp->tsoffset;
4189 #ifdef CONFIG_TCP_MD5SIG
4191 * Parse MD5 Signature option
4193 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
4195 int length = (th->doff << 2) - sizeof(*th);
4196 const u8 *ptr = (const u8 *)(th + 1);
4198 /* If not enough data remaining, we can short cut */
4199 while (length >= TCPOLEN_MD5SIG) {
4200 int opcode = *ptr++;
4211 if (opsize < 2 || opsize > length)
4213 if (opcode == TCPOPT_MD5SIG)
4214 return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
4221 EXPORT_SYMBOL(tcp_parse_md5sig_option);
4224 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
4226 * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
4227 * it can pass through stack. So, the following predicate verifies that
4228 * this segment is not used for anything but congestion avoidance or
4229 * fast retransmit. Moreover, we even are able to eliminate most of such
4230 * second order effects, if we apply some small "replay" window (~RTO)
4231 * to timestamp space.
4233 * All these measures still do not guarantee that we reject wrapped ACKs
4234 * on networks with high bandwidth, when sequence space is recycled fastly,
4235 * but it guarantees that such events will be very rare and do not affect
4236 * connection seriously. This doesn't look nice, but alas, PAWS is really
4239 * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
4240 * states that events when retransmit arrives after original data are rare.
4241 * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
4242 * the biggest problem on large power networks even with minor reordering.
4243 * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
4244 * up to bandwidth of 18Gigabit/sec. 8) ]
4247 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
4249 const struct tcp_sock *tp = tcp_sk(sk);
4250 const struct tcphdr *th = tcp_hdr(skb);
4251 u32 seq = TCP_SKB_CB(skb)->seq;
4252 u32 ack = TCP_SKB_CB(skb)->ack_seq;
4254 return (/* 1. Pure ACK with correct sequence number. */
4255 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
4257 /* 2. ... and duplicate ACK. */
4258 ack == tp->snd_una &&
4260 /* 3. ... and does not update window. */
4261 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
4263 /* 4. ... and sits in replay window. */
4264 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
4267 static inline bool tcp_paws_discard(const struct sock *sk,
4268 const struct sk_buff *skb)
4270 const struct tcp_sock *tp = tcp_sk(sk);
4272 return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
4273 !tcp_disordered_ack(sk, skb);
4276 /* Check segment sequence number for validity.
4278 * Segment controls are considered valid, if the segment
4279 * fits to the window after truncation to the window. Acceptability
4280 * of data (and SYN, FIN, of course) is checked separately.
4281 * See tcp_data_queue(), for example.
4283 * Also, controls (RST is main one) are accepted using RCV.WUP instead
4284 * of RCV.NXT. Peer still did not advance his SND.UNA when we
4285 * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
4286 * (borrowed from freebsd)
4289 static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
4291 return !before(end_seq, tp->rcv_wup) &&
4292 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
4295 /* When we get a reset we do this. */
4296 void tcp_reset(struct sock *sk, struct sk_buff *skb)
4298 trace_tcp_receive_reset(sk);
4300 /* mptcp can't tell us to ignore reset pkts,
4301 * so just ignore the return value of mptcp_incoming_options().
4303 if (sk_is_mptcp(sk))
4304 mptcp_incoming_options(sk, skb);
4306 /* We want the right error as BSD sees it (and indeed as we do). */
4307 switch (sk->sk_state) {
4309 sk->sk_err = ECONNREFUSED;
4311 case TCP_CLOSE_WAIT:
4317 sk->sk_err = ECONNRESET;
4319 /* This barrier is coupled with smp_rmb() in tcp_poll() */
4322 tcp_write_queue_purge(sk);
4325 if (!sock_flag(sk, SOCK_DEAD))
4326 sk_error_report(sk);
4330 * Process the FIN bit. This now behaves as it is supposed to work
4331 * and the FIN takes effect when it is validly part of sequence
4332 * space. Not before when we get holes.
4334 * If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
4335 * (and thence onto LAST-ACK and finally, CLOSE, we never enter
4338 * If we are in FINWAIT-1, a received FIN indicates simultaneous
4339 * close and we go into CLOSING (and later onto TIME-WAIT)
4341 * If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
4343 void tcp_fin(struct sock *sk)
4345 struct tcp_sock *tp = tcp_sk(sk);
4347 inet_csk_schedule_ack(sk);
4349 sk->sk_shutdown |= RCV_SHUTDOWN;
4350 sock_set_flag(sk, SOCK_DONE);
4352 switch (sk->sk_state) {
4354 case TCP_ESTABLISHED:
4355 /* Move to CLOSE_WAIT */
4356 tcp_set_state(sk, TCP_CLOSE_WAIT);
4357 inet_csk_enter_pingpong_mode(sk);
4360 case TCP_CLOSE_WAIT:
4362 /* Received a retransmission of the FIN, do
4367 /* RFC793: Remain in the LAST-ACK state. */
4371 /* This case occurs when a simultaneous close
4372 * happens, we must ack the received FIN and
4373 * enter the CLOSING state.
4376 tcp_set_state(sk, TCP_CLOSING);
4379 /* Received a FIN -- send ACK and enter TIME_WAIT. */
4381 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4384 /* Only TCP_LISTEN and TCP_CLOSE are left, in these
4385 * cases we should never reach this piece of code.
4387 pr_err("%s: Impossible, sk->sk_state=%d\n",
4388 __func__, sk->sk_state);
4392 /* It _is_ possible, that we have something out-of-order _after_ FIN.
4393 * Probably, we should reset in this case. For now drop them.
4395 skb_rbtree_purge(&tp->out_of_order_queue);
4396 if (tcp_is_sack(tp))
4397 tcp_sack_reset(&tp->rx_opt);
4400 if (!sock_flag(sk, SOCK_DEAD)) {
4401 sk->sk_state_change(sk);
4403 /* Do not send POLL_HUP for half duplex close. */
4404 if (sk->sk_shutdown == SHUTDOWN_MASK ||
4405 sk->sk_state == TCP_CLOSE)
4406 sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4408 sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4412 static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4415 if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4416 if (before(seq, sp->start_seq))
4417 sp->start_seq = seq;
4418 if (after(end_seq, sp->end_seq))
4419 sp->end_seq = end_seq;
4425 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4427 struct tcp_sock *tp = tcp_sk(sk);
4429 if (tcp_is_sack(tp) && sock_net(sk)->ipv4.sysctl_tcp_dsack) {
4432 if (before(seq, tp->rcv_nxt))
4433 mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4435 mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4437 NET_INC_STATS(sock_net(sk), mib_idx);
4439 tp->rx_opt.dsack = 1;
4440 tp->duplicate_sack[0].start_seq = seq;
4441 tp->duplicate_sack[0].end_seq = end_seq;
4445 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4447 struct tcp_sock *tp = tcp_sk(sk);
4449 if (!tp->rx_opt.dsack)
4450 tcp_dsack_set(sk, seq, end_seq);
4452 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4455 static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
4457 /* When the ACK path fails or drops most ACKs, the sender would
4458 * timeout and spuriously retransmit the same segment repeatedly.
4459 * The receiver remembers and reflects via DSACKs. Leverage the
4460 * DSACK state and change the txhash to re-route speculatively.
4462 if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq &&
4463 sk_rethink_txhash(sk))
4464 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDUPLICATEDATAREHASH);
4467 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4469 struct tcp_sock *tp = tcp_sk(sk);
4471 if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4472 before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4473 NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4474 tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
4476 if (tcp_is_sack(tp) && sock_net(sk)->ipv4.sysctl_tcp_dsack) {
4477 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4479 tcp_rcv_spurious_retrans(sk, skb);
4480 if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4481 end_seq = tp->rcv_nxt;
4482 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4489 /* These routines update the SACK block as out-of-order packets arrive or
4490 * in-order packets close up the sequence space.
4492 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4495 struct tcp_sack_block *sp = &tp->selective_acks[0];
4496 struct tcp_sack_block *swalk = sp + 1;
4498 /* See if the recent change to the first SACK eats into
4499 * or hits the sequence space of other SACK blocks, if so coalesce.
4501 for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4502 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4505 /* Zap SWALK, by moving every further SACK up by one slot.
4506 * Decrease num_sacks.
4508 tp->rx_opt.num_sacks--;
4509 for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4518 static void tcp_sack_compress_send_ack(struct sock *sk)
4520 struct tcp_sock *tp = tcp_sk(sk);
4522 if (!tp->compressed_ack)
4525 if (hrtimer_try_to_cancel(&tp->compressed_ack_timer) == 1)
4528 /* Since we have to send one ack finally,
4529 * substract one from tp->compressed_ack to keep
4530 * LINUX_MIB_TCPACKCOMPRESSED accurate.
4532 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,
4533 tp->compressed_ack - 1);
4535 tp->compressed_ack = 0;
4539 /* Reasonable amount of sack blocks included in TCP SACK option
4540 * The max is 4, but this becomes 3 if TCP timestamps are there.
4541 * Given that SACK packets might be lost, be conservative and use 2.
4543 #define TCP_SACK_BLOCKS_EXPECTED 2
4545 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4547 struct tcp_sock *tp = tcp_sk(sk);
4548 struct tcp_sack_block *sp = &tp->selective_acks[0];
4549 int cur_sacks = tp->rx_opt.num_sacks;
4555 for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4556 if (tcp_sack_extend(sp, seq, end_seq)) {
4557 if (this_sack >= TCP_SACK_BLOCKS_EXPECTED)
4558 tcp_sack_compress_send_ack(sk);
4559 /* Rotate this_sack to the first one. */
4560 for (; this_sack > 0; this_sack--, sp--)
4561 swap(*sp, *(sp - 1));
4563 tcp_sack_maybe_coalesce(tp);
4568 if (this_sack >= TCP_SACK_BLOCKS_EXPECTED)
4569 tcp_sack_compress_send_ack(sk);
4571 /* Could not find an adjacent existing SACK, build a new one,
4572 * put it at the front, and shift everyone else down. We
4573 * always know there is at least one SACK present already here.
4575 * If the sack array is full, forget about the last one.
4577 if (this_sack >= TCP_NUM_SACKS) {
4579 tp->rx_opt.num_sacks--;
4582 for (; this_sack > 0; this_sack--, sp--)
4586 /* Build the new head SACK, and we're done. */
4587 sp->start_seq = seq;
4588 sp->end_seq = end_seq;
4589 tp->rx_opt.num_sacks++;
4592 /* RCV.NXT advances, some SACKs should be eaten. */
4594 static void tcp_sack_remove(struct tcp_sock *tp)
4596 struct tcp_sack_block *sp = &tp->selective_acks[0];
4597 int num_sacks = tp->rx_opt.num_sacks;
4600 /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4601 if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4602 tp->rx_opt.num_sacks = 0;
4606 for (this_sack = 0; this_sack < num_sacks;) {
4607 /* Check if the start of the sack is covered by RCV.NXT. */
4608 if (!before(tp->rcv_nxt, sp->start_seq)) {
4611 /* RCV.NXT must cover all the block! */
4612 WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4614 /* Zap this SACK, by moving forward any other SACKS. */
4615 for (i = this_sack+1; i < num_sacks; i++)
4616 tp->selective_acks[i-1] = tp->selective_acks[i];
4623 tp->rx_opt.num_sacks = num_sacks;
4627 * tcp_try_coalesce - try to merge skb to prior one
4630 * @from: buffer to add in queue
4631 * @fragstolen: pointer to boolean
4633 * Before queueing skb @from after @to, try to merge them
4634 * to reduce overall memory use and queue lengths, if cost is small.
4635 * Packets in ofo or receive queues can stay a long time.
4636 * Better try to coalesce them right now to avoid future collapses.
4637 * Returns true if caller should free @from instead of queueing it
4639 static bool tcp_try_coalesce(struct sock *sk,
4641 struct sk_buff *from,
4646 *fragstolen = false;
4648 /* Its possible this segment overlaps with prior segment in queue */
4649 if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4652 if (!mptcp_skb_can_collapse(to, from))
4655 #ifdef CONFIG_TLS_DEVICE
4656 if (from->decrypted != to->decrypted)
4660 if (!skb_try_coalesce(to, from, fragstolen, &delta))
4663 atomic_add(delta, &sk->sk_rmem_alloc);
4664 sk_mem_charge(sk, delta);
4665 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4666 TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4667 TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
4668 TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
4670 if (TCP_SKB_CB(from)->has_rxtstamp) {
4671 TCP_SKB_CB(to)->has_rxtstamp = true;
4672 to->tstamp = from->tstamp;
4673 skb_hwtstamps(to)->hwtstamp = skb_hwtstamps(from)->hwtstamp;
4679 static bool tcp_ooo_try_coalesce(struct sock *sk,
4681 struct sk_buff *from,
4684 bool res = tcp_try_coalesce(sk, to, from, fragstolen);
4686 /* In case tcp_drop_reason() is called later, update to->gso_segs */
4688 u32 gso_segs = max_t(u16, 1, skb_shinfo(to)->gso_segs) +
4689 max_t(u16, 1, skb_shinfo(from)->gso_segs);
4691 skb_shinfo(to)->gso_segs = min_t(u32, gso_segs, 0xFFFF);
4696 static void tcp_drop_reason(struct sock *sk, struct sk_buff *skb,
4697 enum skb_drop_reason reason)
4699 sk_drops_add(sk, skb);
4700 kfree_skb_reason(skb, reason);
4703 /* This one checks to see if we can put data from the
4704 * out_of_order queue into the receive_queue.
4706 static void tcp_ofo_queue(struct sock *sk)
4708 struct tcp_sock *tp = tcp_sk(sk);
4709 __u32 dsack_high = tp->rcv_nxt;
4710 bool fin, fragstolen, eaten;
4711 struct sk_buff *skb, *tail;
4714 p = rb_first(&tp->out_of_order_queue);
4717 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4720 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4721 __u32 dsack = dsack_high;
4722 if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4723 dsack_high = TCP_SKB_CB(skb)->end_seq;
4724 tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4727 rb_erase(&skb->rbnode, &tp->out_of_order_queue);
4729 if (unlikely(!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))) {
4730 tcp_drop_reason(sk, skb, SKB_DROP_REASON_TCP_OFO_DROP);
4734 tail = skb_peek_tail(&sk->sk_receive_queue);
4735 eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
4736 tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4737 fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
4739 __skb_queue_tail(&sk->sk_receive_queue, skb);
4741 kfree_skb_partial(skb, fragstolen);
4743 if (unlikely(fin)) {
4745 /* tcp_fin() purges tp->out_of_order_queue,
4746 * so we must end this loop right now.
4753 static bool tcp_prune_ofo_queue(struct sock *sk);
4754 static int tcp_prune_queue(struct sock *sk);
4756 static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
4759 if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4760 !sk_rmem_schedule(sk, skb, size)) {
4762 if (tcp_prune_queue(sk) < 0)
4765 while (!sk_rmem_schedule(sk, skb, size)) {
4766 if (!tcp_prune_ofo_queue(sk))
4773 static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
4775 struct tcp_sock *tp = tcp_sk(sk);
4776 struct rb_node **p, *parent;
4777 struct sk_buff *skb1;
4781 tcp_ecn_check_ce(sk, skb);
4783 if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
4784 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);
4785 sk->sk_data_ready(sk);
4786 tcp_drop_reason(sk, skb, SKB_DROP_REASON_PROTO_MEM);
4790 /* Disable header prediction. */
4792 inet_csk_schedule_ack(sk);
4794 tp->rcv_ooopack += max_t(u16, 1, skb_shinfo(skb)->gso_segs);
4795 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
4796 seq = TCP_SKB_CB(skb)->seq;
4797 end_seq = TCP_SKB_CB(skb)->end_seq;
4799 p = &tp->out_of_order_queue.rb_node;
4800 if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4801 /* Initial out of order segment, build 1 SACK. */
4802 if (tcp_is_sack(tp)) {
4803 tp->rx_opt.num_sacks = 1;
4804 tp->selective_acks[0].start_seq = seq;
4805 tp->selective_acks[0].end_seq = end_seq;
4807 rb_link_node(&skb->rbnode, NULL, p);
4808 rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
4809 tp->ooo_last_skb = skb;
4813 /* In the typical case, we are adding an skb to the end of the list.
4814 * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
4816 if (tcp_ooo_try_coalesce(sk, tp->ooo_last_skb,
4817 skb, &fragstolen)) {
4819 /* For non sack flows, do not grow window to force DUPACK
4820 * and trigger fast retransmit.
4822 if (tcp_is_sack(tp))
4823 tcp_grow_window(sk, skb, true);
4824 kfree_skb_partial(skb, fragstolen);
4828 /* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */
4829 if (!before(seq, TCP_SKB_CB(tp->ooo_last_skb)->end_seq)) {
4830 parent = &tp->ooo_last_skb->rbnode;
4831 p = &parent->rb_right;
4835 /* Find place to insert this segment. Handle overlaps on the way. */
4839 skb1 = rb_to_skb(parent);
4840 if (before(seq, TCP_SKB_CB(skb1)->seq)) {
4841 p = &parent->rb_left;
4844 if (before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4845 if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4846 /* All the bits are present. Drop. */
4847 NET_INC_STATS(sock_net(sk),
4848 LINUX_MIB_TCPOFOMERGE);
4849 tcp_drop_reason(sk, skb,
4850 SKB_DROP_REASON_TCP_OFOMERGE);
4852 tcp_dsack_set(sk, seq, end_seq);
4855 if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4856 /* Partial overlap. */
4857 tcp_dsack_set(sk, seq, TCP_SKB_CB(skb1)->end_seq);
4859 /* skb's seq == skb1's seq and skb covers skb1.
4860 * Replace skb1 with skb.
4862 rb_replace_node(&skb1->rbnode, &skb->rbnode,
4863 &tp->out_of_order_queue);
4864 tcp_dsack_extend(sk,
4865 TCP_SKB_CB(skb1)->seq,
4866 TCP_SKB_CB(skb1)->end_seq);
4867 NET_INC_STATS(sock_net(sk),
4868 LINUX_MIB_TCPOFOMERGE);
4869 tcp_drop_reason(sk, skb1,
4870 SKB_DROP_REASON_TCP_OFOMERGE);
4873 } else if (tcp_ooo_try_coalesce(sk, skb1,
4874 skb, &fragstolen)) {
4877 p = &parent->rb_right;
4880 /* Insert segment into RB tree. */
4881 rb_link_node(&skb->rbnode, parent, p);
4882 rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
4885 /* Remove other segments covered by skb. */
4886 while ((skb1 = skb_rb_next(skb)) != NULL) {
4887 if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4889 if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4890 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4894 rb_erase(&skb1->rbnode, &tp->out_of_order_queue);
4895 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4896 TCP_SKB_CB(skb1)->end_seq);
4897 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4898 tcp_drop_reason(sk, skb1, SKB_DROP_REASON_TCP_OFOMERGE);
4900 /* If there is no skb after us, we are the last_skb ! */
4902 tp->ooo_last_skb = skb;
4905 if (tcp_is_sack(tp))
4906 tcp_sack_new_ofo_skb(sk, seq, end_seq);
4909 /* For non sack flows, do not grow window to force DUPACK
4910 * and trigger fast retransmit.
4912 if (tcp_is_sack(tp))
4913 tcp_grow_window(sk, skb, false);
4915 skb_set_owner_r(skb, sk);
4919 static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb,
4923 struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
4926 tcp_try_coalesce(sk, tail,
4927 skb, fragstolen)) ? 1 : 0;
4928 tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
4930 __skb_queue_tail(&sk->sk_receive_queue, skb);
4931 skb_set_owner_r(skb, sk);
4936 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
4938 struct sk_buff *skb;
4946 if (size > PAGE_SIZE) {
4947 int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);
4949 data_len = npages << PAGE_SHIFT;
4950 size = data_len + (size & ~PAGE_MASK);
4952 skb = alloc_skb_with_frags(size - data_len, data_len,
4953 PAGE_ALLOC_COSTLY_ORDER,
4954 &err, sk->sk_allocation);
4958 skb_put(skb, size - data_len);
4959 skb->data_len = data_len;
4962 if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
4963 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
4967 err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
4971 TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
4972 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
4973 TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
4975 if (tcp_queue_rcv(sk, skb, &fragstolen)) {
4976 WARN_ON_ONCE(fragstolen); /* should not happen */
4988 void tcp_data_ready(struct sock *sk)
4990 if (tcp_epollin_ready(sk, sk->sk_rcvlowat) || sock_flag(sk, SOCK_DONE))
4991 sk->sk_data_ready(sk);
4994 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4996 struct tcp_sock *tp = tcp_sk(sk);
4997 enum skb_drop_reason reason;
5001 /* If a subflow has been reset, the packet should not continue
5002 * to be processed, drop the packet.
5004 if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb)) {
5009 if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
5014 __skb_pull(skb, tcp_hdr(skb)->doff * 4);
5016 reason = SKB_DROP_REASON_NOT_SPECIFIED;
5017 tp->rx_opt.dsack = 0;
5019 /* Queue data for delivery to the user.
5020 * Packets in sequence go to the receive queue.
5021 * Out of sequence packets to the out_of_order_queue.
5023 if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
5024 if (tcp_receive_window(tp) == 0) {
5025 reason = SKB_DROP_REASON_TCP_ZEROWINDOW;
5026 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
5030 /* Ok. In sequence. In window. */
5032 if (skb_queue_len(&sk->sk_receive_queue) == 0)
5033 sk_forced_mem_schedule(sk, skb->truesize);
5034 else if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
5035 reason = SKB_DROP_REASON_PROTO_MEM;
5036 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
5037 sk->sk_data_ready(sk);
5041 eaten = tcp_queue_rcv(sk, skb, &fragstolen);
5043 tcp_event_data_recv(sk, skb);
5044 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
5047 if (!RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5050 /* RFC5681. 4.2. SHOULD send immediate ACK, when
5051 * gap in queue is filled.
5053 if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
5054 inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
5057 if (tp->rx_opt.num_sacks)
5058 tcp_sack_remove(tp);
5060 tcp_fast_path_check(sk);
5063 kfree_skb_partial(skb, fragstolen);
5064 if (!sock_flag(sk, SOCK_DEAD))
5069 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
5070 tcp_rcv_spurious_retrans(sk, skb);
5071 /* A retransmit, 2nd most common case. Force an immediate ack. */
5072 reason = SKB_DROP_REASON_TCP_OLD_DATA;
5073 NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
5074 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
5077 tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
5078 inet_csk_schedule_ack(sk);
5080 tcp_drop_reason(sk, skb, reason);
5084 /* Out of window. F.e. zero window probe. */
5085 if (!before(TCP_SKB_CB(skb)->seq,
5086 tp->rcv_nxt + tcp_receive_window(tp))) {
5087 reason = SKB_DROP_REASON_TCP_OVERWINDOW;
5091 if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
5092 /* Partial packet, seq < rcv_next < end_seq */
5093 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
5095 /* If window is closed, drop tail of packet. But after
5096 * remembering D-SACK for its head made in previous line.
5098 if (!tcp_receive_window(tp)) {
5099 reason = SKB_DROP_REASON_TCP_ZEROWINDOW;
5100 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
5106 tcp_data_queue_ofo(sk, skb);
5109 static struct sk_buff *tcp_skb_next(struct sk_buff *skb, struct sk_buff_head *list)
5112 return !skb_queue_is_last(list, skb) ? skb->next : NULL;
5114 return skb_rb_next(skb);
5117 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
5118 struct sk_buff_head *list,
5119 struct rb_root *root)
5121 struct sk_buff *next = tcp_skb_next(skb, list);
5124 __skb_unlink(skb, list);
5126 rb_erase(&skb->rbnode, root);
5129 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
5134 /* Insert skb into rb tree, ordered by TCP_SKB_CB(skb)->seq */
5135 void tcp_rbtree_insert(struct rb_root *root, struct sk_buff *skb)
5137 struct rb_node **p = &root->rb_node;
5138 struct rb_node *parent = NULL;
5139 struct sk_buff *skb1;
5143 skb1 = rb_to_skb(parent);
5144 if (before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb1)->seq))
5145 p = &parent->rb_left;
5147 p = &parent->rb_right;
5149 rb_link_node(&skb->rbnode, parent, p);
5150 rb_insert_color(&skb->rbnode, root);
5153 /* Collapse contiguous sequence of skbs head..tail with
5154 * sequence numbers start..end.
5156 * If tail is NULL, this means until the end of the queue.
5158 * Segments with FIN/SYN are not collapsed (only because this
5162 tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
5163 struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end)
5165 struct sk_buff *skb = head, *n;
5166 struct sk_buff_head tmp;
5169 /* First, check that queue is collapsible and find
5170 * the point where collapsing can be useful.
5173 for (end_of_skbs = true; skb != NULL && skb != tail; skb = n) {
5174 n = tcp_skb_next(skb, list);
5176 /* No new bits? It is possible on ofo queue. */
5177 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
5178 skb = tcp_collapse_one(sk, skb, list, root);
5184 /* The first skb to collapse is:
5186 * - bloated or contains data before "start" or
5187 * overlaps to the next one and mptcp allow collapsing.
5189 if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
5190 (tcp_win_from_space(sk, skb->truesize) > skb->len ||
5191 before(TCP_SKB_CB(skb)->seq, start))) {
5192 end_of_skbs = false;
5196 if (n && n != tail && mptcp_skb_can_collapse(skb, n) &&
5197 TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(n)->seq) {
5198 end_of_skbs = false;
5202 /* Decided to skip this, advance start seq. */
5203 start = TCP_SKB_CB(skb)->end_seq;
5206 (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
5209 __skb_queue_head_init(&tmp);
5211 while (before(start, end)) {
5212 int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
5213 struct sk_buff *nskb;
5215 nskb = alloc_skb(copy, GFP_ATOMIC);
5219 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
5220 #ifdef CONFIG_TLS_DEVICE
5221 nskb->decrypted = skb->decrypted;
5223 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
5225 __skb_queue_before(list, skb, nskb);
5227 __skb_queue_tail(&tmp, nskb); /* defer rbtree insertion */
5228 skb_set_owner_r(nskb, sk);
5229 mptcp_skb_ext_move(nskb, skb);
5231 /* Copy data, releasing collapsed skbs. */
5233 int offset = start - TCP_SKB_CB(skb)->seq;
5234 int size = TCP_SKB_CB(skb)->end_seq - start;
5238 size = min(copy, size);
5239 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
5241 TCP_SKB_CB(nskb)->end_seq += size;
5245 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
5246 skb = tcp_collapse_one(sk, skb, list, root);
5249 !mptcp_skb_can_collapse(nskb, skb) ||
5250 (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
5252 #ifdef CONFIG_TLS_DEVICE
5253 if (skb->decrypted != nskb->decrypted)
5260 skb_queue_walk_safe(&tmp, skb, n)
5261 tcp_rbtree_insert(root, skb);
5264 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
5265 * and tcp_collapse() them until all the queue is collapsed.
5267 static void tcp_collapse_ofo_queue(struct sock *sk)
5269 struct tcp_sock *tp = tcp_sk(sk);
5270 u32 range_truesize, sum_tiny = 0;
5271 struct sk_buff *skb, *head;
5274 skb = skb_rb_first(&tp->out_of_order_queue);
5277 tp->ooo_last_skb = skb_rb_last(&tp->out_of_order_queue);
5280 start = TCP_SKB_CB(skb)->seq;
5281 end = TCP_SKB_CB(skb)->end_seq;
5282 range_truesize = skb->truesize;
5284 for (head = skb;;) {
5285 skb = skb_rb_next(skb);
5287 /* Range is terminated when we see a gap or when
5288 * we are at the queue end.
5291 after(TCP_SKB_CB(skb)->seq, end) ||
5292 before(TCP_SKB_CB(skb)->end_seq, start)) {
5293 /* Do not attempt collapsing tiny skbs */
5294 if (range_truesize != head->truesize ||
5295 end - start >= SKB_WITH_OVERHEAD(SK_MEM_QUANTUM)) {
5296 tcp_collapse(sk, NULL, &tp->out_of_order_queue,
5297 head, skb, start, end);
5299 sum_tiny += range_truesize;
5300 if (sum_tiny > sk->sk_rcvbuf >> 3)
5306 range_truesize += skb->truesize;
5307 if (unlikely(before(TCP_SKB_CB(skb)->seq, start)))
5308 start = TCP_SKB_CB(skb)->seq;
5309 if (after(TCP_SKB_CB(skb)->end_seq, end))
5310 end = TCP_SKB_CB(skb)->end_seq;
5315 * Clean the out-of-order queue to make room.
5316 * We drop high sequences packets to :
5317 * 1) Let a chance for holes to be filled.
5318 * 2) not add too big latencies if thousands of packets sit there.
5319 * (But if application shrinks SO_RCVBUF, we could still end up
5320 * freeing whole queue here)
5321 * 3) Drop at least 12.5 % of sk_rcvbuf to avoid malicious attacks.
5323 * Return true if queue has shrunk.
5325 static bool tcp_prune_ofo_queue(struct sock *sk)
5327 struct tcp_sock *tp = tcp_sk(sk);
5328 struct rb_node *node, *prev;
5331 if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
5334 NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED);
5335 goal = sk->sk_rcvbuf >> 3;
5336 node = &tp->ooo_last_skb->rbnode;
5338 prev = rb_prev(node);
5339 rb_erase(node, &tp->out_of_order_queue);
5340 goal -= rb_to_skb(node)->truesize;
5341 tcp_drop_reason(sk, rb_to_skb(node),
5342 SKB_DROP_REASON_TCP_OFO_QUEUE_PRUNE);
5343 if (!prev || goal <= 0) {
5345 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
5346 !tcp_under_memory_pressure(sk))
5348 goal = sk->sk_rcvbuf >> 3;
5352 tp->ooo_last_skb = rb_to_skb(prev);
5354 /* Reset SACK state. A conforming SACK implementation will
5355 * do the same at a timeout based retransmit. When a connection
5356 * is in a sad state like this, we care only about integrity
5357 * of the connection not performance.
5359 if (tp->rx_opt.sack_ok)
5360 tcp_sack_reset(&tp->rx_opt);
5364 /* Reduce allocated memory if we can, trying to get
5365 * the socket within its memory limits again.
5367 * Return less than zero if we should start dropping frames
5368 * until the socket owning process reads some of the data
5369 * to stabilize the situation.
5371 static int tcp_prune_queue(struct sock *sk)
5373 struct tcp_sock *tp = tcp_sk(sk);
5375 NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED);
5377 if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
5378 tcp_clamp_window(sk);
5379 else if (tcp_under_memory_pressure(sk))
5380 tcp_adjust_rcv_ssthresh(sk);
5382 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5385 tcp_collapse_ofo_queue(sk);
5386 if (!skb_queue_empty(&sk->sk_receive_queue))
5387 tcp_collapse(sk, &sk->sk_receive_queue, NULL,
5388 skb_peek(&sk->sk_receive_queue),
5390 tp->copied_seq, tp->rcv_nxt);
5393 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5396 /* Collapsing did not help, destructive actions follow.
5397 * This must not ever occur. */
5399 tcp_prune_ofo_queue(sk);
5401 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5404 /* If we are really being abused, tell the caller to silently
5405 * drop receive data on the floor. It will get retransmitted
5406 * and hopefully then we'll have sufficient space.
5408 NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED);
5410 /* Massive buffer overcommit. */
5415 static bool tcp_should_expand_sndbuf(struct sock *sk)
5417 const struct tcp_sock *tp = tcp_sk(sk);
5419 /* If the user specified a specific send buffer setting, do
5422 if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
5425 /* If we are under global TCP memory pressure, do not expand. */
5426 if (tcp_under_memory_pressure(sk)) {
5427 int unused_mem = sk_unused_reserved_mem(sk);
5429 /* Adjust sndbuf according to reserved mem. But make sure
5430 * it never goes below SOCK_MIN_SNDBUF.
5431 * See sk_stream_moderate_sndbuf() for more details.
5433 if (unused_mem > SOCK_MIN_SNDBUF)
5434 WRITE_ONCE(sk->sk_sndbuf, unused_mem);
5439 /* If we are under soft global TCP memory pressure, do not expand. */
5440 if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
5443 /* If we filled the congestion window, do not expand. */
5444 if (tcp_packets_in_flight(tp) >= tcp_snd_cwnd(tp))
5450 static void tcp_new_space(struct sock *sk)
5452 struct tcp_sock *tp = tcp_sk(sk);
5454 if (tcp_should_expand_sndbuf(sk)) {
5455 tcp_sndbuf_expand(sk);
5456 tp->snd_cwnd_stamp = tcp_jiffies32;
5459 INDIRECT_CALL_1(sk->sk_write_space, sk_stream_write_space, sk);
5462 /* Caller made space either from:
5463 * 1) Freeing skbs in rtx queues (after tp->snd_una has advanced)
5464 * 2) Sent skbs from output queue (and thus advancing tp->snd_nxt)
5466 * We might be able to generate EPOLLOUT to the application if:
5467 * 1) Space consumed in output/rtx queues is below sk->sk_sndbuf/2
5468 * 2) notsent amount (tp->write_seq - tp->snd_nxt) became
5469 * small enough that tcp_stream_memory_free() decides it
5470 * is time to generate EPOLLOUT.
5472 void tcp_check_space(struct sock *sk)
5474 /* pairs with tcp_poll() */
5476 if (sk->sk_socket &&
5477 test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
5479 if (!test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
5480 tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
5484 static inline void tcp_data_snd_check(struct sock *sk)
5486 tcp_push_pending_frames(sk);
5487 tcp_check_space(sk);
5491 * Check if sending an ack is needed.
5493 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
5495 struct tcp_sock *tp = tcp_sk(sk);
5496 unsigned long rtt, delay;
5498 /* More than one full frame received... */
5499 if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
5500 /* ... and right edge of window advances far enough.
5501 * (tcp_recvmsg() will send ACK otherwise).
5502 * If application uses SO_RCVLOWAT, we want send ack now if
5503 * we have not received enough bytes to satisfy the condition.
5505 (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat ||
5506 __tcp_select_window(sk) >= tp->rcv_wnd)) ||
5507 /* We ACK each frame or... */
5508 tcp_in_quickack_mode(sk) ||
5509 /* Protocol state mandates a one-time immediate ACK */
5510 inet_csk(sk)->icsk_ack.pending & ICSK_ACK_NOW) {
5516 if (!ofo_possible || RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5517 tcp_send_delayed_ack(sk);
5521 if (!tcp_is_sack(tp) ||
5522 tp->compressed_ack >= sock_net(sk)->ipv4.sysctl_tcp_comp_sack_nr)
5525 if (tp->compressed_ack_rcv_nxt != tp->rcv_nxt) {
5526 tp->compressed_ack_rcv_nxt = tp->rcv_nxt;
5527 tp->dup_ack_counter = 0;
5529 if (tp->dup_ack_counter < TCP_FASTRETRANS_THRESH) {
5530 tp->dup_ack_counter++;
5533 tp->compressed_ack++;
5534 if (hrtimer_is_queued(&tp->compressed_ack_timer))
5537 /* compress ack timer : 5 % of rtt, but no more than tcp_comp_sack_delay_ns */
5539 rtt = tp->rcv_rtt_est.rtt_us;
5540 if (tp->srtt_us && tp->srtt_us < rtt)
5543 delay = min_t(unsigned long, sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns,
5544 rtt * (NSEC_PER_USEC >> 3)/20);
5546 hrtimer_start_range_ns(&tp->compressed_ack_timer, ns_to_ktime(delay),
5547 sock_net(sk)->ipv4.sysctl_tcp_comp_sack_slack_ns,
5548 HRTIMER_MODE_REL_PINNED_SOFT);
5551 static inline void tcp_ack_snd_check(struct sock *sk)
5553 if (!inet_csk_ack_scheduled(sk)) {
5554 /* We sent a data segment already. */
5557 __tcp_ack_snd_check(sk, 1);
5561 * This routine is only called when we have urgent data
5562 * signaled. Its the 'slow' part of tcp_urg. It could be
5563 * moved inline now as tcp_urg is only called from one
5564 * place. We handle URGent data wrong. We have to - as
5565 * BSD still doesn't use the correction from RFC961.
5566 * For 1003.1g we should support a new option TCP_STDURG to permit
5567 * either form (or just set the sysctl tcp_stdurg).
5570 static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
5572 struct tcp_sock *tp = tcp_sk(sk);
5573 u32 ptr = ntohs(th->urg_ptr);
5575 if (ptr && !READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_stdurg))
5577 ptr += ntohl(th->seq);
5579 /* Ignore urgent data that we've already seen and read. */
5580 if (after(tp->copied_seq, ptr))
5583 /* Do not replay urg ptr.
5585 * NOTE: interesting situation not covered by specs.
5586 * Misbehaving sender may send urg ptr, pointing to segment,
5587 * which we already have in ofo queue. We are not able to fetch
5588 * such data and will stay in TCP_URG_NOTYET until will be eaten
5589 * by recvmsg(). Seems, we are not obliged to handle such wicked
5590 * situations. But it is worth to think about possibility of some
5591 * DoSes using some hypothetical application level deadlock.
5593 if (before(ptr, tp->rcv_nxt))
5596 /* Do we already have a newer (or duplicate) urgent pointer? */
5597 if (tp->urg_data && !after(ptr, tp->urg_seq))
5600 /* Tell the world about our new urgent pointer. */
5603 /* We may be adding urgent data when the last byte read was
5604 * urgent. To do this requires some care. We cannot just ignore
5605 * tp->copied_seq since we would read the last urgent byte again
5606 * as data, nor can we alter copied_seq until this data arrives
5607 * or we break the semantics of SIOCATMARK (and thus sockatmark())
5609 * NOTE. Double Dutch. Rendering to plain English: author of comment
5610 * above did something sort of send("A", MSG_OOB); send("B", MSG_OOB);
5611 * and expect that both A and B disappear from stream. This is _wrong_.
5612 * Though this happens in BSD with high probability, this is occasional.
5613 * Any application relying on this is buggy. Note also, that fix "works"
5614 * only in this artificial test. Insert some normal data between A and B and we will
5615 * decline of BSD again. Verdict: it is better to remove to trap
5618 if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
5619 !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
5620 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
5622 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
5623 __skb_unlink(skb, &sk->sk_receive_queue);
5628 WRITE_ONCE(tp->urg_data, TCP_URG_NOTYET);
5629 WRITE_ONCE(tp->urg_seq, ptr);
5631 /* Disable header prediction. */
5635 /* This is the 'fast' part of urgent handling. */
5636 static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
5638 struct tcp_sock *tp = tcp_sk(sk);
5640 /* Check if we get a new urgent pointer - normally not. */
5641 if (unlikely(th->urg))
5642 tcp_check_urg(sk, th);
5644 /* Do we wait for any urgent data? - normally not... */
5645 if (unlikely(tp->urg_data == TCP_URG_NOTYET)) {
5646 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
5649 /* Is the urgent pointer pointing into this packet? */
5650 if (ptr < skb->len) {
5652 if (skb_copy_bits(skb, ptr, &tmp, 1))
5654 WRITE_ONCE(tp->urg_data, TCP_URG_VALID | tmp);
5655 if (!sock_flag(sk, SOCK_DEAD))
5656 sk->sk_data_ready(sk);
5661 /* Accept RST for rcv_nxt - 1 after a FIN.
5662 * When tcp connections are abruptly terminated from Mac OSX (via ^C), a
5663 * FIN is sent followed by a RST packet. The RST is sent with the same
5664 * sequence number as the FIN, and thus according to RFC 5961 a challenge
5665 * ACK should be sent. However, Mac OSX rate limits replies to challenge
5666 * ACKs on the closed socket. In addition middleboxes can drop either the
5667 * challenge ACK or a subsequent RST.
5669 static bool tcp_reset_check(const struct sock *sk, const struct sk_buff *skb)
5671 struct tcp_sock *tp = tcp_sk(sk);
5673 return unlikely(TCP_SKB_CB(skb)->seq == (tp->rcv_nxt - 1) &&
5674 (1 << sk->sk_state) & (TCPF_CLOSE_WAIT | TCPF_LAST_ACK |
5678 /* Does PAWS and seqno based validation of an incoming segment, flags will
5679 * play significant role here.
5681 static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5682 const struct tcphdr *th, int syn_inerr)
5684 struct tcp_sock *tp = tcp_sk(sk);
5687 /* RFC1323: H1. Apply PAWS check first. */
5688 if (tcp_fast_parse_options(sock_net(sk), skb, th, tp) &&
5689 tp->rx_opt.saw_tstamp &&
5690 tcp_paws_discard(sk, skb)) {
5692 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5693 if (!tcp_oow_rate_limited(sock_net(sk), skb,
5694 LINUX_MIB_TCPACKSKIPPEDPAWS,
5695 &tp->last_oow_ack_time))
5696 tcp_send_dupack(sk, skb);
5697 SKB_DR_SET(reason, TCP_RFC7323_PAWS);
5700 /* Reset is accepted even if it did not pass PAWS. */
5703 /* Step 1: check sequence number */
5704 if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5705 /* RFC793, page 37: "In all states except SYN-SENT, all reset
5706 * (RST) segments are validated by checking their SEQ-fields."
5707 * And page 69: "If an incoming segment is not acceptable,
5708 * an acknowledgment should be sent in reply (unless the RST
5709 * bit is set, if so drop the segment and return)".
5714 if (!tcp_oow_rate_limited(sock_net(sk), skb,
5715 LINUX_MIB_TCPACKSKIPPEDSEQ,
5716 &tp->last_oow_ack_time))
5717 tcp_send_dupack(sk, skb);
5718 } else if (tcp_reset_check(sk, skb)) {
5721 SKB_DR_SET(reason, TCP_INVALID_SEQUENCE);
5725 /* Step 2: check RST bit */
5727 /* RFC 5961 3.2 (extend to match against (RCV.NXT - 1) after a
5728 * FIN and SACK too if available):
5729 * If seq num matches RCV.NXT or (RCV.NXT - 1) after a FIN, or
5730 * the right-most SACK block,
5732 * RESET the connection
5734 * Send a challenge ACK
5736 if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt ||
5737 tcp_reset_check(sk, skb))
5740 if (tcp_is_sack(tp) && tp->rx_opt.num_sacks > 0) {
5741 struct tcp_sack_block *sp = &tp->selective_acks[0];
5742 int max_sack = sp[0].end_seq;
5745 for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;
5747 max_sack = after(sp[this_sack].end_seq,
5749 sp[this_sack].end_seq : max_sack;
5752 if (TCP_SKB_CB(skb)->seq == max_sack)
5756 /* Disable TFO if RST is out-of-order
5757 * and no data has been received
5758 * for current active TFO socket
5760 if (tp->syn_fastopen && !tp->data_segs_in &&
5761 sk->sk_state == TCP_ESTABLISHED)
5762 tcp_fastopen_active_disable(sk);
5763 tcp_send_challenge_ack(sk);
5764 SKB_DR_SET(reason, TCP_RESET);
5768 /* step 3: check security and precedence [ignored] */
5770 /* step 4: Check for a SYN
5771 * RFC 5961 4.2 : Send a challenge ack
5776 TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
5777 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
5778 tcp_send_challenge_ack(sk);
5779 SKB_DR_SET(reason, TCP_INVALID_SYN);
5783 bpf_skops_parse_hdr(sk, skb);
5788 tcp_drop_reason(sk, skb, reason);
5798 * TCP receive function for the ESTABLISHED state.
5800 * It is split into a fast path and a slow path. The fast path is
5802 * - A zero window was announced from us - zero window probing
5803 * is only handled properly in the slow path.
5804 * - Out of order segments arrived.
5805 * - Urgent data is expected.
5806 * - There is no buffer space left
5807 * - Unexpected TCP flags/window values/header lengths are received
5808 * (detected by checking the TCP header against pred_flags)
5809 * - Data is sent in both directions. Fast path only supports pure senders
5810 * or pure receivers (this means either the sequence number or the ack
5811 * value must stay constant)
5812 * - Unexpected TCP option.
5814 * When these conditions are not satisfied it drops into a standard
5815 * receive procedure patterned after RFC793 to handle all cases.
5816 * The first three cases are guaranteed by proper pred_flags setting,
5817 * the rest is checked inline. Fast processing is turned on in
5818 * tcp_data_queue when everything is OK.
5820 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
5822 enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
5823 const struct tcphdr *th = (const struct tcphdr *)skb->data;
5824 struct tcp_sock *tp = tcp_sk(sk);
5825 unsigned int len = skb->len;
5827 /* TCP congestion window tracking */
5828 trace_tcp_probe(sk, skb);
5830 tcp_mstamp_refresh(tp);
5831 if (unlikely(!rcu_access_pointer(sk->sk_rx_dst)))
5832 inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
5834 * Header prediction.
5835 * The code loosely follows the one in the famous
5836 * "30 instruction TCP receive" Van Jacobson mail.
5838 * Van's trick is to deposit buffers into socket queue
5839 * on a device interrupt, to call tcp_recv function
5840 * on the receive process context and checksum and copy
5841 * the buffer to user space. smart...
5843 * Our current scheme is not silly either but we take the
5844 * extra cost of the net_bh soft interrupt processing...
5845 * We do checksum and copy also but from device to kernel.
5848 tp->rx_opt.saw_tstamp = 0;
5850 /* pred_flags is 0xS?10 << 16 + snd_wnd
5851 * if header_prediction is to be made
5852 * 'S' will always be tp->tcp_header_len >> 2
5853 * '?' will be 0 for the fast path, otherwise pred_flags is 0 to
5854 * turn it off (when there are holes in the receive
5855 * space for instance)
5856 * PSH flag is ignored.
5859 if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5860 TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5861 !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5862 int tcp_header_len = tp->tcp_header_len;
5864 /* Timestamp header prediction: tcp_header_len
5865 * is automatically equal to th->doff*4 due to pred_flags
5869 /* Check timestamp */
5870 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5871 /* No? Slow path! */
5872 if (!tcp_parse_aligned_timestamp(tp, th))
5875 /* If PAWS failed, check it more carefully in slow path */
5876 if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5879 /* DO NOT update ts_recent here, if checksum fails
5880 * and timestamp was corrupted part, it will result
5881 * in a hung connection since we will drop all
5882 * future packets due to the PAWS test.
5886 if (len <= tcp_header_len) {
5887 /* Bulk data transfer: sender */
5888 if (len == tcp_header_len) {
5889 /* Predicted packet is in window by definition.
5890 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5891 * Hence, check seq<=rcv_wup reduces to:
5893 if (tcp_header_len ==
5894 (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5895 tp->rcv_nxt == tp->rcv_wup)
5896 tcp_store_ts_recent(tp);
5898 /* We know that such packets are checksummed
5901 tcp_ack(sk, skb, 0);
5903 tcp_data_snd_check(sk);
5904 /* When receiving pure ack in fast path, update
5905 * last ts ecr directly instead of calling
5906 * tcp_rcv_rtt_measure_ts()
5908 tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
5910 } else { /* Header too small */
5911 reason = SKB_DROP_REASON_PKT_TOO_SMALL;
5912 TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
5917 bool fragstolen = false;
5919 if (tcp_checksum_complete(skb))
5922 if ((int)skb->truesize > sk->sk_forward_alloc)
5925 /* Predicted packet is in window by definition.
5926 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5927 * Hence, check seq<=rcv_wup reduces to:
5929 if (tcp_header_len ==
5930 (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5931 tp->rcv_nxt == tp->rcv_wup)
5932 tcp_store_ts_recent(tp);
5934 tcp_rcv_rtt_measure_ts(sk, skb);
5936 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS);
5938 /* Bulk data transfer: receiver */
5940 __skb_pull(skb, tcp_header_len);
5941 eaten = tcp_queue_rcv(sk, skb, &fragstolen);
5943 tcp_event_data_recv(sk, skb);
5945 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5946 /* Well, only one small jumplet in fast path... */
5947 tcp_ack(sk, skb, FLAG_DATA);
5948 tcp_data_snd_check(sk);
5949 if (!inet_csk_ack_scheduled(sk))
5952 tcp_update_wl(tp, TCP_SKB_CB(skb)->seq);
5955 __tcp_ack_snd_check(sk, 0);
5958 kfree_skb_partial(skb, fragstolen);
5965 if (len < (th->doff << 2) || tcp_checksum_complete(skb))
5968 if (!th->ack && !th->rst && !th->syn) {
5969 reason = SKB_DROP_REASON_TCP_FLAGS;
5974 * Standard slow path.
5977 if (!tcp_validate_incoming(sk, skb, th, 1))
5981 reason = tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT);
5982 if ((int)reason < 0) {
5986 tcp_rcv_rtt_measure_ts(sk, skb);
5988 /* Process urgent data. */
5989 tcp_urg(sk, skb, th);
5991 /* step 7: process the segment text */
5992 tcp_data_queue(sk, skb);
5994 tcp_data_snd_check(sk);
5995 tcp_ack_snd_check(sk);
5999 reason = SKB_DROP_REASON_TCP_CSUM;
6000 trace_tcp_bad_csum(skb);
6001 TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
6002 TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
6005 tcp_drop_reason(sk, skb, reason);
6007 EXPORT_SYMBOL(tcp_rcv_established);
6009 void tcp_init_transfer(struct sock *sk, int bpf_op, struct sk_buff *skb)
6011 struct inet_connection_sock *icsk = inet_csk(sk);
6012 struct tcp_sock *tp = tcp_sk(sk);
6015 icsk->icsk_af_ops->rebuild_header(sk);
6016 tcp_init_metrics(sk);
6018 /* Initialize the congestion window to start the transfer.
6019 * Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
6020 * retransmitted. In light of RFC6298 more aggressive 1sec
6021 * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
6022 * retransmission has occurred.
6024 if (tp->total_retrans > 1 && tp->undo_marker)
6025 tcp_snd_cwnd_set(tp, 1);
6027 tcp_snd_cwnd_set(tp, tcp_init_cwnd(tp, __sk_dst_get(sk)));
6028 tp->snd_cwnd_stamp = tcp_jiffies32;
6030 bpf_skops_established(sk, bpf_op, skb);
6031 /* Initialize congestion control unless BPF initialized it already: */
6032 if (!icsk->icsk_ca_initialized)
6033 tcp_init_congestion_control(sk);
6034 tcp_init_buffer_space(sk);
6037 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
6039 struct tcp_sock *tp = tcp_sk(sk);
6040 struct inet_connection_sock *icsk = inet_csk(sk);
6042 tcp_set_state(sk, TCP_ESTABLISHED);
6043 icsk->icsk_ack.lrcvtime = tcp_jiffies32;
6046 icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
6047 security_inet_conn_established(sk, skb);
6048 sk_mark_napi_id(sk, skb);
6051 tcp_init_transfer(sk, BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB, skb);
6053 /* Prevent spurious tcp_cwnd_restart() on first data
6056 tp->lsndtime = tcp_jiffies32;
6058 if (sock_flag(sk, SOCK_KEEPOPEN))
6059 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
6061 if (!tp->rx_opt.snd_wscale)
6062 __tcp_fast_path_on(tp, tp->snd_wnd);
6067 static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
6068 struct tcp_fastopen_cookie *cookie)
6070 struct tcp_sock *tp = tcp_sk(sk);
6071 struct sk_buff *data = tp->syn_data ? tcp_rtx_queue_head(sk) : NULL;
6072 u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
6073 bool syn_drop = false;
6075 if (mss == tp->rx_opt.user_mss) {
6076 struct tcp_options_received opt;
6078 /* Get original SYNACK MSS value if user MSS sets mss_clamp */
6079 tcp_clear_options(&opt);
6080 opt.user_mss = opt.mss_clamp = 0;
6081 tcp_parse_options(sock_net(sk), synack, &opt, 0, NULL);
6082 mss = opt.mss_clamp;
6085 if (!tp->syn_fastopen) {
6086 /* Ignore an unsolicited cookie */
6088 } else if (tp->total_retrans) {
6089 /* SYN timed out and the SYN-ACK neither has a cookie nor
6090 * acknowledges data. Presumably the remote received only
6091 * the retransmitted (regular) SYNs: either the original
6092 * SYN-data or the corresponding SYN-ACK was dropped.
6094 syn_drop = (cookie->len < 0 && data);
6095 } else if (cookie->len < 0 && !tp->syn_data) {
6096 /* We requested a cookie but didn't get it. If we did not use
6097 * the (old) exp opt format then try so next time (try_exp=1).
6098 * Otherwise we go back to use the RFC7413 opt (try_exp=2).
6100 try_exp = tp->syn_fastopen_exp ? 2 : 1;
6103 tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
6105 if (data) { /* Retransmit unacked data in SYN */
6106 if (tp->total_retrans)
6107 tp->fastopen_client_fail = TFO_SYN_RETRANSMITTED;
6109 tp->fastopen_client_fail = TFO_DATA_NOT_ACKED;
6110 skb_rbtree_walk_from(data)
6111 tcp_mark_skb_lost(sk, data);
6112 tcp_xmit_retransmit_queue(sk);
6113 NET_INC_STATS(sock_net(sk),
6114 LINUX_MIB_TCPFASTOPENACTIVEFAIL);
6117 tp->syn_data_acked = tp->syn_data;
6118 if (tp->syn_data_acked) {
6119 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
6120 /* SYN-data is counted as two separate packets in tcp_ack() */
6121 if (tp->delivered > 1)
6125 tcp_fastopen_add_skb(sk, synack);
6130 static void smc_check_reset_syn(struct tcp_sock *tp)
6132 #if IS_ENABLED(CONFIG_SMC)
6133 if (static_branch_unlikely(&tcp_have_smc)) {
6134 if (tp->syn_smc && !tp->rx_opt.smc_ok)
6140 static void tcp_try_undo_spurious_syn(struct sock *sk)
6142 struct tcp_sock *tp = tcp_sk(sk);
6145 /* undo_marker is set when SYN or SYNACK times out. The timeout is
6146 * spurious if the ACK's timestamp option echo value matches the
6147 * original SYN timestamp.
6149 syn_stamp = tp->retrans_stamp;
6150 if (tp->undo_marker && syn_stamp && tp->rx_opt.saw_tstamp &&
6151 syn_stamp == tp->rx_opt.rcv_tsecr)
6152 tp->undo_marker = 0;
6155 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
6156 const struct tcphdr *th)
6158 struct inet_connection_sock *icsk = inet_csk(sk);
6159 struct tcp_sock *tp = tcp_sk(sk);
6160 struct tcp_fastopen_cookie foc = { .len = -1 };
6161 int saved_clamp = tp->rx_opt.mss_clamp;
6165 tcp_parse_options(sock_net(sk), skb, &tp->rx_opt, 0, &foc);
6166 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
6167 tp->rx_opt.rcv_tsecr -= tp->tsoffset;
6171 * "If the state is SYN-SENT then
6172 * first check the ACK bit
6173 * If the ACK bit is set
6174 * If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
6175 * a reset (unless the RST bit is set, if so drop
6176 * the segment and return)"
6178 if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
6179 after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
6180 /* Previous FIN/ACK or RST/ACK might be ignored. */
6181 if (icsk->icsk_retransmits == 0)
6182 inet_csk_reset_xmit_timer(sk,
6184 TCP_TIMEOUT_MIN, TCP_RTO_MAX);
6185 goto reset_and_undo;
6188 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
6189 !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
6190 tcp_time_stamp(tp))) {
6191 NET_INC_STATS(sock_net(sk),
6192 LINUX_MIB_PAWSACTIVEREJECTED);
6193 goto reset_and_undo;
6196 /* Now ACK is acceptable.
6198 * "If the RST bit is set
6199 * If the ACK was acceptable then signal the user "error:
6200 * connection reset", drop the segment, enter CLOSED state,
6201 * delete TCB, and return."
6212 * "fifth, if neither of the SYN or RST bits is set then
6213 * drop the segment and return."
6219 SKB_DR_SET(reason, TCP_FLAGS);
6220 goto discard_and_undo;
6223 * "If the SYN bit is on ...
6224 * are acceptable then ...
6225 * (our SYN has been ACKed), change the connection
6226 * state to ESTABLISHED..."
6229 tcp_ecn_rcv_synack(tp, th);
6231 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
6232 tcp_try_undo_spurious_syn(sk);
6233 tcp_ack(sk, skb, FLAG_SLOWPATH);
6235 /* Ok.. it's good. Set up sequence numbers and
6236 * move to established.
6238 WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
6239 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
6241 /* RFC1323: The window in SYN & SYN/ACK segments is
6244 tp->snd_wnd = ntohs(th->window);
6246 if (!tp->rx_opt.wscale_ok) {
6247 tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
6248 tp->window_clamp = min(tp->window_clamp, 65535U);
6251 if (tp->rx_opt.saw_tstamp) {
6252 tp->rx_opt.tstamp_ok = 1;
6253 tp->tcp_header_len =
6254 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
6255 tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
6256 tcp_store_ts_recent(tp);
6258 tp->tcp_header_len = sizeof(struct tcphdr);
6261 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
6262 tcp_initialize_rcv_mss(sk);
6264 /* Remember, tcp_poll() does not lock socket!
6265 * Change state from SYN-SENT only after copied_seq
6266 * is initialized. */
6267 WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6269 smc_check_reset_syn(tp);
6273 tcp_finish_connect(sk, skb);
6275 fastopen_fail = (tp->syn_fastopen || tp->syn_data) &&
6276 tcp_rcv_fastopen_synack(sk, skb, &foc);
6278 if (!sock_flag(sk, SOCK_DEAD)) {
6279 sk->sk_state_change(sk);
6280 sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
6284 if (sk->sk_write_pending ||
6285 icsk->icsk_accept_queue.rskq_defer_accept ||
6286 inet_csk_in_pingpong_mode(sk)) {
6287 /* Save one ACK. Data will be ready after
6288 * several ticks, if write_pending is set.
6290 * It may be deleted, but with this feature tcpdumps
6291 * look so _wonderfully_ clever, that I was not able
6292 * to stand against the temptation 8) --ANK
6294 inet_csk_schedule_ack(sk);
6295 tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
6296 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
6297 TCP_DELACK_MAX, TCP_RTO_MAX);
6304 /* No ACK in the segment */
6308 * "If the RST bit is set
6310 * Otherwise (no ACK) drop the segment and return."
6312 SKB_DR_SET(reason, TCP_RESET);
6313 goto discard_and_undo;
6317 if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
6318 tcp_paws_reject(&tp->rx_opt, 0)) {
6319 SKB_DR_SET(reason, TCP_RFC7323_PAWS);
6320 goto discard_and_undo;
6323 /* We see SYN without ACK. It is attempt of
6324 * simultaneous connect with crossed SYNs.
6325 * Particularly, it can be connect to self.
6327 tcp_set_state(sk, TCP_SYN_RECV);
6329 if (tp->rx_opt.saw_tstamp) {
6330 tp->rx_opt.tstamp_ok = 1;
6331 tcp_store_ts_recent(tp);
6332 tp->tcp_header_len =
6333 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
6335 tp->tcp_header_len = sizeof(struct tcphdr);
6338 WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
6339 WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6340 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
6342 /* RFC1323: The window in SYN & SYN/ACK segments is
6345 tp->snd_wnd = ntohs(th->window);
6346 tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
6347 tp->max_window = tp->snd_wnd;
6349 tcp_ecn_rcv_syn(tp, th);
6352 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
6353 tcp_initialize_rcv_mss(sk);
6355 tcp_send_synack(sk);
6357 /* Note, we could accept data and URG from this segment.
6358 * There are no obstacles to make this (except that we must
6359 * either change tcp_recvmsg() to prevent it from returning data
6360 * before 3WHS completes per RFC793, or employ TCP Fast Open).
6362 * However, if we ignore data in ACKless segments sometimes,
6363 * we have no reasons to accept it sometimes.
6364 * Also, seems the code doing it in step6 of tcp_rcv_state_process
6365 * is not flawless. So, discard packet for sanity.
6366 * Uncomment this return to process the data.
6373 /* "fifth, if neither of the SYN or RST bits is set then
6374 * drop the segment and return."
6378 tcp_clear_options(&tp->rx_opt);
6379 tp->rx_opt.mss_clamp = saved_clamp;
6380 tcp_drop_reason(sk, skb, reason);
6384 tcp_clear_options(&tp->rx_opt);
6385 tp->rx_opt.mss_clamp = saved_clamp;
6389 static void tcp_rcv_synrecv_state_fastopen(struct sock *sk)
6391 struct request_sock *req;
6393 /* If we are still handling the SYNACK RTO, see if timestamp ECR allows
6394 * undo. If peer SACKs triggered fast recovery, we can't undo here.
6396 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
6397 tcp_try_undo_loss(sk, false);
6399 /* Reset rtx states to prevent spurious retransmits_timed_out() */
6400 tcp_sk(sk)->retrans_stamp = 0;
6401 inet_csk(sk)->icsk_retransmits = 0;
6403 /* Once we leave TCP_SYN_RECV or TCP_FIN_WAIT_1,
6404 * we no longer need req so release it.
6406 req = rcu_dereference_protected(tcp_sk(sk)->fastopen_rsk,
6407 lockdep_sock_is_held(sk));
6408 reqsk_fastopen_remove(sk, req, false);
6410 /* Re-arm the timer because data may have been sent out.
6411 * This is similar to the regular data transmission case
6412 * when new data has just been ack'ed.
6414 * (TFO) - we could try to be more aggressive and
6415 * retransmitting any data sooner based on when they
6422 * This function implements the receiving procedure of RFC 793 for
6423 * all states except ESTABLISHED and TIME_WAIT.
6424 * It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
6425 * address independent.
6428 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
6430 struct tcp_sock *tp = tcp_sk(sk);
6431 struct inet_connection_sock *icsk = inet_csk(sk);
6432 const struct tcphdr *th = tcp_hdr(skb);
6433 struct request_sock *req;
6438 switch (sk->sk_state) {
6440 SKB_DR_SET(reason, TCP_CLOSE);
6448 SKB_DR_SET(reason, TCP_RESET);
6453 SKB_DR_SET(reason, TCP_FLAGS);
6456 /* It is possible that we process SYN packets from backlog,
6457 * so we need to make sure to disable BH and RCU right there.
6461 acceptable = icsk->icsk_af_ops->conn_request(sk, skb) >= 0;
6470 SKB_DR_SET(reason, TCP_FLAGS);
6474 tp->rx_opt.saw_tstamp = 0;
6475 tcp_mstamp_refresh(tp);
6476 queued = tcp_rcv_synsent_state_process(sk, skb, th);
6480 /* Do step6 onward by hand. */
6481 tcp_urg(sk, skb, th);
6483 tcp_data_snd_check(sk);
6487 tcp_mstamp_refresh(tp);
6488 tp->rx_opt.saw_tstamp = 0;
6489 req = rcu_dereference_protected(tp->fastopen_rsk,
6490 lockdep_sock_is_held(sk));
6494 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
6495 sk->sk_state != TCP_FIN_WAIT1);
6497 if (!tcp_check_req(sk, skb, req, true, &req_stolen)) {
6498 SKB_DR_SET(reason, TCP_FASTOPEN);
6503 if (!th->ack && !th->rst && !th->syn) {
6504 SKB_DR_SET(reason, TCP_FLAGS);
6507 if (!tcp_validate_incoming(sk, skb, th, 0))
6510 /* step 5: check the ACK field */
6511 acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
6512 FLAG_UPDATE_TS_RECENT |
6513 FLAG_NO_CHALLENGE_ACK) > 0;
6516 if (sk->sk_state == TCP_SYN_RECV)
6517 return 1; /* send one RST */
6518 tcp_send_challenge_ack(sk);
6519 SKB_DR_SET(reason, TCP_OLD_ACK);
6522 switch (sk->sk_state) {
6524 tp->delivered++; /* SYN-ACK delivery isn't tracked in tcp_ack */
6526 tcp_synack_rtt_meas(sk, req);
6529 tcp_rcv_synrecv_state_fastopen(sk);
6531 tcp_try_undo_spurious_syn(sk);
6532 tp->retrans_stamp = 0;
6533 tcp_init_transfer(sk, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB,
6535 WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6538 tcp_set_state(sk, TCP_ESTABLISHED);
6539 sk->sk_state_change(sk);
6541 /* Note, that this wakeup is only for marginal crossed SYN case.
6542 * Passively open sockets are not waked up, because
6543 * sk->sk_sleep == NULL and sk->sk_socket == NULL.
6546 sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
6548 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
6549 tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
6550 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
6552 if (tp->rx_opt.tstamp_ok)
6553 tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
6555 if (!inet_csk(sk)->icsk_ca_ops->cong_control)
6556 tcp_update_pacing_rate(sk);
6558 /* Prevent spurious tcp_cwnd_restart() on first data packet */
6559 tp->lsndtime = tcp_jiffies32;
6561 tcp_initialize_rcv_mss(sk);
6562 tcp_fast_path_on(tp);
6565 case TCP_FIN_WAIT1: {
6569 tcp_rcv_synrecv_state_fastopen(sk);
6571 if (tp->snd_una != tp->write_seq)
6574 tcp_set_state(sk, TCP_FIN_WAIT2);
6575 sk->sk_shutdown |= SEND_SHUTDOWN;
6579 if (!sock_flag(sk, SOCK_DEAD)) {
6580 /* Wake up lingering close() */
6581 sk->sk_state_change(sk);
6585 if (tp->linger2 < 0) {
6587 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6590 if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6591 after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
6592 /* Receive out of order FIN after close() */
6593 if (tp->syn_fastopen && th->fin)
6594 tcp_fastopen_active_disable(sk);
6596 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6600 tmo = tcp_fin_time(sk);
6601 if (tmo > TCP_TIMEWAIT_LEN) {
6602 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
6603 } else if (th->fin || sock_owned_by_user(sk)) {
6604 /* Bad case. We could lose such FIN otherwise.
6605 * It is not a big problem, but it looks confusing
6606 * and not so rare event. We still can lose it now,
6607 * if it spins in bh_lock_sock(), but it is really
6610 inet_csk_reset_keepalive_timer(sk, tmo);
6612 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
6619 if (tp->snd_una == tp->write_seq) {
6620 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
6626 if (tp->snd_una == tp->write_seq) {
6627 tcp_update_metrics(sk);
6634 /* step 6: check the URG bit */
6635 tcp_urg(sk, skb, th);
6637 /* step 7: process the segment text */
6638 switch (sk->sk_state) {
6639 case TCP_CLOSE_WAIT:
6642 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
6643 /* If a subflow has been reset, the packet should not
6644 * continue to be processed, drop the packet.
6646 if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb))
6653 /* RFC 793 says to queue data in these states,
6654 * RFC 1122 says we MUST send a reset.
6655 * BSD 4.4 also does reset.
6657 if (sk->sk_shutdown & RCV_SHUTDOWN) {
6658 if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6659 after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
6660 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6666 case TCP_ESTABLISHED:
6667 tcp_data_queue(sk, skb);
6672 /* tcp_data could move socket to TIME-WAIT */
6673 if (sk->sk_state != TCP_CLOSE) {
6674 tcp_data_snd_check(sk);
6675 tcp_ack_snd_check(sk);
6680 tcp_drop_reason(sk, skb, reason);
6688 EXPORT_SYMBOL(tcp_rcv_state_process);
6690 static inline void pr_drop_req(struct request_sock *req, __u16 port, int family)
6692 struct inet_request_sock *ireq = inet_rsk(req);
6694 if (family == AF_INET)
6695 net_dbg_ratelimited("drop open request from %pI4/%u\n",
6696 &ireq->ir_rmt_addr, port);
6697 #if IS_ENABLED(CONFIG_IPV6)
6698 else if (family == AF_INET6)
6699 net_dbg_ratelimited("drop open request from %pI6/%u\n",
6700 &ireq->ir_v6_rmt_addr, port);
6704 /* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set
6706 * If we receive a SYN packet with these bits set, it means a
6707 * network is playing bad games with TOS bits. In order to
6708 * avoid possible false congestion notifications, we disable
6709 * TCP ECN negotiation.
6711 * Exception: tcp_ca wants ECN. This is required for DCTCP
6712 * congestion control: Linux DCTCP asserts ECT on all packets,
6713 * including SYN, which is most optimal solution; however,
6714 * others, such as FreeBSD do not.
6716 * Exception: At least one of the reserved bits of the TCP header (th->res1) is
6717 * set, indicating the use of a future TCP extension (such as AccECN). See
6718 * RFC8311 §4.3 which updates RFC3168 to allow the development of such
6721 static void tcp_ecn_create_request(struct request_sock *req,
6722 const struct sk_buff *skb,
6723 const struct sock *listen_sk,
6724 const struct dst_entry *dst)
6726 const struct tcphdr *th = tcp_hdr(skb);
6727 const struct net *net = sock_net(listen_sk);
6728 bool th_ecn = th->ece && th->cwr;
6735 ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
6736 ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
6737 ecn_ok = READ_ONCE(net->ipv4.sysctl_tcp_ecn) || ecn_ok_dst;
6739 if (((!ect || th->res1) && ecn_ok) || tcp_ca_needs_ecn(listen_sk) ||
6740 (ecn_ok_dst & DST_FEATURE_ECN_CA) ||
6741 tcp_bpf_ca_needs_ecn((struct sock *)req))
6742 inet_rsk(req)->ecn_ok = 1;
6745 static void tcp_openreq_init(struct request_sock *req,
6746 const struct tcp_options_received *rx_opt,
6747 struct sk_buff *skb, const struct sock *sk)
6749 struct inet_request_sock *ireq = inet_rsk(req);
6751 req->rsk_rcv_wnd = 0; /* So that tcp_send_synack() knows! */
6752 tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
6753 tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
6754 tcp_rsk(req)->snt_synack = 0;
6755 tcp_rsk(req)->last_oow_ack_time = 0;
6756 req->mss = rx_opt->mss_clamp;
6757 req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
6758 ireq->tstamp_ok = rx_opt->tstamp_ok;
6759 ireq->sack_ok = rx_opt->sack_ok;
6760 ireq->snd_wscale = rx_opt->snd_wscale;
6761 ireq->wscale_ok = rx_opt->wscale_ok;
6764 ireq->ir_rmt_port = tcp_hdr(skb)->source;
6765 ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
6766 ireq->ir_mark = inet_request_mark(sk, skb);
6767 #if IS_ENABLED(CONFIG_SMC)
6768 ireq->smc_ok = rx_opt->smc_ok && !(tcp_sk(sk)->smc_hs_congested &&
6769 tcp_sk(sk)->smc_hs_congested(sk));
6773 struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
6774 struct sock *sk_listener,
6775 bool attach_listener)
6777 struct request_sock *req = reqsk_alloc(ops, sk_listener,
6781 struct inet_request_sock *ireq = inet_rsk(req);
6783 ireq->ireq_opt = NULL;
6784 #if IS_ENABLED(CONFIG_IPV6)
6785 ireq->pktopts = NULL;
6787 atomic64_set(&ireq->ir_cookie, 0);
6788 ireq->ireq_state = TCP_NEW_SYN_RECV;
6789 write_pnet(&ireq->ireq_net, sock_net(sk_listener));
6790 ireq->ireq_family = sk_listener->sk_family;
6791 req->timeout = TCP_TIMEOUT_INIT;
6796 EXPORT_SYMBOL(inet_reqsk_alloc);
6799 * Return true if a syncookie should be sent
6801 static bool tcp_syn_flood_action(const struct sock *sk, const char *proto)
6803 struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
6804 const char *msg = "Dropping request";
6805 struct net *net = sock_net(sk);
6806 bool want_cookie = false;
6809 syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
6811 #ifdef CONFIG_SYN_COOKIES
6813 msg = "Sending cookies";
6815 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
6818 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
6820 if (!queue->synflood_warned && syncookies != 2 &&
6821 xchg(&queue->synflood_warned, 1) == 0)
6822 net_info_ratelimited("%s: Possible SYN flooding on port %d. %s. Check SNMP counters.\n",
6823 proto, sk->sk_num, msg);
6828 static void tcp_reqsk_record_syn(const struct sock *sk,
6829 struct request_sock *req,
6830 const struct sk_buff *skb)
6832 if (tcp_sk(sk)->save_syn) {
6833 u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);
6834 struct saved_syn *saved_syn;
6838 if (tcp_sk(sk)->save_syn == 2) { /* Save full header. */
6839 base = skb_mac_header(skb);
6840 mac_hdrlen = skb_mac_header_len(skb);
6843 base = skb_network_header(skb);
6847 saved_syn = kmalloc(struct_size(saved_syn, data, len),
6850 saved_syn->mac_hdrlen = mac_hdrlen;
6851 saved_syn->network_hdrlen = skb_network_header_len(skb);
6852 saved_syn->tcp_hdrlen = tcp_hdrlen(skb);
6853 memcpy(saved_syn->data, base, len);
6854 req->saved_syn = saved_syn;
6859 /* If a SYN cookie is required and supported, returns a clamped MSS value to be
6860 * used for SYN cookie generation.
6862 u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
6863 const struct tcp_request_sock_ops *af_ops,
6864 struct sock *sk, struct tcphdr *th)
6866 struct tcp_sock *tp = tcp_sk(sk);
6869 if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) != 2 &&
6870 !inet_csk_reqsk_queue_is_full(sk))
6873 if (!tcp_syn_flood_action(sk, rsk_ops->slab_name))
6876 if (sk_acceptq_is_full(sk)) {
6877 NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
6881 mss = tcp_parse_mss_option(th, tp->rx_opt.user_mss);
6883 mss = af_ops->mss_clamp;
6887 EXPORT_SYMBOL_GPL(tcp_get_syncookie_mss);
6889 int tcp_conn_request(struct request_sock_ops *rsk_ops,
6890 const struct tcp_request_sock_ops *af_ops,
6891 struct sock *sk, struct sk_buff *skb)
6893 struct tcp_fastopen_cookie foc = { .len = -1 };
6894 __u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn;
6895 struct tcp_options_received tmp_opt;
6896 struct tcp_sock *tp = tcp_sk(sk);
6897 struct net *net = sock_net(sk);
6898 struct sock *fastopen_sk = NULL;
6899 struct request_sock *req;
6900 bool want_cookie = false;
6901 struct dst_entry *dst;
6905 syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
6907 /* TW buckets are converted to open requests without
6908 * limitations, they conserve resources and peer is
6909 * evidently real one.
6911 if ((syncookies == 2 || inet_csk_reqsk_queue_is_full(sk)) && !isn) {
6912 want_cookie = tcp_syn_flood_action(sk, rsk_ops->slab_name);
6917 if (sk_acceptq_is_full(sk)) {
6918 NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
6922 req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);
6926 req->syncookie = want_cookie;
6927 tcp_rsk(req)->af_specific = af_ops;
6928 tcp_rsk(req)->ts_off = 0;
6929 #if IS_ENABLED(CONFIG_MPTCP)
6930 tcp_rsk(req)->is_mptcp = 0;
6933 tcp_clear_options(&tmp_opt);
6934 tmp_opt.mss_clamp = af_ops->mss_clamp;
6935 tmp_opt.user_mss = tp->rx_opt.user_mss;
6936 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0,
6937 want_cookie ? NULL : &foc);
6939 if (want_cookie && !tmp_opt.saw_tstamp)
6940 tcp_clear_options(&tmp_opt);
6942 if (IS_ENABLED(CONFIG_SMC) && want_cookie)
6945 tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
6946 tcp_openreq_init(req, &tmp_opt, skb, sk);
6947 inet_rsk(req)->no_srccheck = inet_sk(sk)->transparent;
6949 /* Note: tcp_v6_init_req() might override ir_iif for link locals */
6950 inet_rsk(req)->ir_iif = inet_request_bound_dev_if(sk, skb);
6952 dst = af_ops->route_req(sk, skb, &fl, req);
6956 if (tmp_opt.tstamp_ok)
6957 tcp_rsk(req)->ts_off = af_ops->init_ts_off(net, skb);
6959 if (!want_cookie && !isn) {
6960 int max_syn_backlog = READ_ONCE(net->ipv4.sysctl_max_syn_backlog);
6962 /* Kill the following clause, if you dislike this way. */
6964 (max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
6965 (max_syn_backlog >> 2)) &&
6966 !tcp_peer_is_proven(req, dst)) {
6967 /* Without syncookies last quarter of
6968 * backlog is filled with destinations,
6969 * proven to be alive.
6970 * It means that we continue to communicate
6971 * to destinations, already remembered
6972 * to the moment of synflood.
6974 pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
6976 goto drop_and_release;
6979 isn = af_ops->init_seq(skb);
6982 tcp_ecn_create_request(req, skb, sk, dst);
6985 isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
6986 if (!tmp_opt.tstamp_ok)
6987 inet_rsk(req)->ecn_ok = 0;
6990 tcp_rsk(req)->snt_isn = isn;
6991 tcp_rsk(req)->txhash = net_tx_rndhash();
6992 tcp_rsk(req)->syn_tos = TCP_SKB_CB(skb)->ip_dsfield;
6993 tcp_openreq_init_rwin(req, sk, dst);
6994 sk_rx_queue_set(req_to_sk(req), skb);
6996 tcp_reqsk_record_syn(sk, req, skb);
6997 fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
7000 af_ops->send_synack(fastopen_sk, dst, &fl, req,
7001 &foc, TCP_SYNACK_FASTOPEN, skb);
7002 /* Add the child socket directly into the accept queue */
7003 if (!inet_csk_reqsk_queue_add(sk, req, fastopen_sk)) {
7004 reqsk_fastopen_remove(fastopen_sk, req, false);
7005 bh_unlock_sock(fastopen_sk);
7006 sock_put(fastopen_sk);
7009 sk->sk_data_ready(sk);
7010 bh_unlock_sock(fastopen_sk);
7011 sock_put(fastopen_sk);
7013 tcp_rsk(req)->tfo_listener = false;
7015 req->timeout = tcp_timeout_init((struct sock *)req);
7016 inet_csk_reqsk_queue_hash_add(sk, req, req->timeout);
7018 af_ops->send_synack(sk, dst, &fl, req, &foc,
7019 !want_cookie ? TCP_SYNACK_NORMAL :
7038 EXPORT_SYMBOL(tcp_conn_request);