slirp/tcp_input.c

   1 /*
   2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  *
  29  *      @(#)tcp_input.c 8.5 (Berkeley) 4/10/94
  30  * tcp_input.c,v 1.10 1994/10/13 18:36:32 wollman Exp
  31  */
  32
  33 /*
  34  * Changes and additions relating to SLiRP
  35  * Copyright (c) 1995 Danny Gasparovski.
  36  *
  37  * Please read the file COPYRIGHT for the
  38  * terms and conditions of the copyright.
  39  */
  40
  41 #include <slirp.h>
  42 #include "ip_icmp.h"
  43
  44 #define TCPREXMTTHRESH 3
  45
  46 #define TCP_PAWS_IDLE   (24 * 24 * 60 * 60 * PR_SLOWHZ)
  47
  48 /* for modulo comparisons of timestamps */
  49 #define TSTMP_LT(a,b)   ((int)((a)-(b)) < 0)
  50 #define TSTMP_GEQ(a,b)  ((int)((a)-(b)) >= 0)
  51
  52 /*
  53  * Insert segment ti into reassembly queue of tcp with
  54  * control block tp.  Return TH_FIN if reassembly now includes
  55  * a segment with FIN.  The macro form does the common case inline
  56  * (segment is the next to be received on an established connection,
  57  * and the queue is empty), avoiding linkage into and removal
  58  * from the queue and repetition of various conversions.
  59  * Set DELACK for segments received in order, but ack immediately
  60  * when segments are out of order (so fast retransmit can work).
  61  */
  62 #ifdef TCP_ACK_HACK
  63 #define TCP_REASS(tp, ti, m, so, flags) {\
  64        if ((ti)->ti_seq == (tp)->rcv_nxt && \
  65            tcpfrag_list_empty(tp) && \
  66            (tp)->t_state == TCPS_ESTABLISHED) {\
  67                if (ti->ti_flags & TH_PUSH) \
  68                        tp->t_flags |= TF_ACKNOW; \
  69                else \
  70                        tp->t_flags |= TF_DELACK; \
  71                (tp)->rcv_nxt += (ti)->ti_len; \
  72                flags = (ti)->ti_flags & TH_FIN; \
  73                if (so->so_emu) { \
  74                        if (tcp_emu((so),(m))) sbappend((so), (m)); \
  75                } else \
  76                        sbappend((so), (m)); \
  77         } else {\
  78                (flags) = tcp_reass((tp), (ti), (m)); \
  79                tp->t_flags |= TF_ACKNOW; \
  80        } \
  81 }
  82 #else
  83 #define TCP_REASS(tp, ti, m, so, flags) { \
  84         if ((ti)->ti_seq == (tp)->rcv_nxt && \
  85         tcpfrag_list_empty(tp) && \
  86             (tp)->t_state == TCPS_ESTABLISHED) { \
  87                 tp->t_flags |= TF_DELACK; \
  88                 (tp)->rcv_nxt += (ti)->ti_len; \
  89                 flags = (ti)->ti_flags & TH_FIN; \
  90                 if (so->so_emu) { \
  91                         if (tcp_emu((so),(m))) sbappend(so, (m)); \
  92                 } else \
  93                         sbappend((so), (m)); \
  94         } else { \
  95                 (flags) = tcp_reass((tp), (ti), (m)); \
  96                 tp->t_flags |= TF_ACKNOW; \
  97         } \
  98 }
  99 #endif
 100 static void tcp_dooptions(struct tcpcb *tp, u_char *cp, int cnt,
 101                           struct tcpiphdr *ti);
 102 static void tcp_xmit_timer(register struct tcpcb *tp, int rtt);
 103
 104 static int
 105 tcp_reass(register struct tcpcb *tp, register struct tcpiphdr *ti,
 106           struct mbuf *m)
 107 {
 108         register struct tcpiphdr *q;
 109         struct socket *so = tp->t_socket;
 110         int flags;
 111
 112         /*
 113          * Call with ti==NULL after become established to
 114          * force pre-ESTABLISHED data up to user socket.
 115          */
 116         if (ti == NULL)
 117                 goto present;
 118
 119         /*
 120          * Find a segment which begins after this one does.
 121          */
 122         for (q = tcpfrag_list_first(tp); !tcpfrag_list_end(q, tp);
 123             q = tcpiphdr_next(q))
 124                 if (SEQ_GT(q->ti_seq, ti->ti_seq))
 125                         break;
 126
 127         /*
 128          * If there is a preceding segment, it may provide some of
 129          * our data already.  If so, drop the data from the incoming
 130          * segment.  If it provides all of our data, drop us.
 131          */
 132         if (!tcpfrag_list_end(tcpiphdr_prev(q), tp)) {
 133                 register int i;
 134                 q = tcpiphdr_prev(q);
 135                 /* conversion to int (in i) handles seq wraparound */
 136                 i = q->ti_seq + q->ti_len - ti->ti_seq;
 137                 if (i > 0) {
 138                         if (i >= ti->ti_len) {
 139                                 m_freem(m);
 140                                 /*
 141                                  * Try to present any queued data
 142                                  * at the left window edge to the user.
 143                                  * This is needed after the 3-WHS
 144                                  * completes.
 145                                  */
 146                                 goto present;   /* ??? */
 147                         }
 148                         m_adj(m, i);
 149                         ti->ti_len -= i;
 150                         ti->ti_seq += i;
 151                 }
 152                 q = tcpiphdr_next(q);
 153         }
 154         ti->ti_mbuf = m;
 155
 156         /*
 157          * While we overlap succeeding segments trim them or,
 158          * if they are completely covered, dequeue them.
 159          */
 160         while (!tcpfrag_list_end(q, tp)) {
 161                 register int i = (ti->ti_seq + ti->ti_len) - q->ti_seq;
 162                 if (i <= 0)
 163                         break;
 164                 if (i < q->ti_len) {
 165                         q->ti_seq += i;
 166                         q->ti_len -= i;
 167                         m_adj(q->ti_mbuf, i);
 168                         break;
 169                 }
 170                 q = tcpiphdr_next(q);
 171                 m = tcpiphdr_prev(q)->ti_mbuf;
 172                 remque(tcpiphdr2qlink(tcpiphdr_prev(q)));
 173                 m_freem(m);
 174         }
 175
 176         /*
 177          * Stick new segment in its place.
 178          */
 179         insque(tcpiphdr2qlink(ti), tcpiphdr2qlink(tcpiphdr_prev(q)));
 180
 181 present:
 182         /*
 183          * Present data to user, advancing rcv_nxt through
 184          * completed sequence space.
 185          */
 186         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 187                 return (0);
 188         ti = tcpfrag_list_first(tp);
 189         if (tcpfrag_list_end(ti, tp) || ti->ti_seq != tp->rcv_nxt)
 190                 return (0);
 191         if (tp->t_state == TCPS_SYN_RECEIVED && ti->ti_len)
 192                 return (0);
 193         do {
 194                 tp->rcv_nxt += ti->ti_len;
 195                 flags = ti->ti_flags & TH_FIN;
 196                 remque(tcpiphdr2qlink(ti));
 197                 m = ti->ti_mbuf;
 198                 ti = tcpiphdr_next(ti);
 199                 if (so->so_state & SS_FCANTSENDMORE)
 200                         m_freem(m);
 201                 else {
 202                         if (so->so_emu) {
 203                                 if (tcp_emu(so,m)) sbappend(so, m);
 204                         } else
 205                                 sbappend(so, m);
 206                 }
 207         } while (ti != (struct tcpiphdr *)tp && ti->ti_seq == tp->rcv_nxt);
 208         return (flags);
 209 }
 210
 211 /*
 212  * TCP input routine, follows pages 65-76 of the
 213  * protocol specification dated September, 1981 very closely.
 214  */
 215 void
 216 tcp_input(struct mbuf *m, int iphlen, struct socket *inso)
 217 {
 218         struct ip save_ip, *ip;
 219         register struct tcpiphdr *ti;
 220         caddr_t optp = NULL;
 221         int optlen = 0;
 222         int len, tlen, off;
 223         register struct tcpcb *tp = NULL;
 224         register int tiflags;
 225         struct socket *so = NULL;
 226         int todrop, acked, ourfinisacked, needoutput = 0;
 227         int iss = 0;
 228         u_long tiwin;
 229         int ret;
 230     struct ex_list *ex_ptr;
 231     Slirp *slirp;
 232
 233         DEBUG_CALL("tcp_input");
 234         DEBUG_ARGS((dfd," m = %8lx  iphlen = %2d  inso = %lx\n",
 235                     (long )m, iphlen, (long )inso ));
 236
 237         /*
 238          * If called with m == 0, then we're continuing the connect
 239          */
 240         if (m == NULL) {
 241                 so = inso;
 242                 slirp = so->slirp;
 243
 244                 /* Re-set a few variables */
 245                 tp = sototcpcb(so);
 246                 m = so->so_m;
 247                 so->so_m = NULL;
 248                 ti = so->so_ti;
 249                 tiwin = ti->ti_win;
 250                 tiflags = ti->ti_flags;
 251
 252                 goto cont_conn;
 253         }
 254         slirp = m->slirp;
 255
 256         /*
 257          * Get IP and TCP header together in first mbuf.
 258          * Note: IP leaves IP header in first mbuf.
 259          */
 260         ti = mtod(m, struct tcpiphdr *);
 261         if (iphlen > sizeof(struct ip )) {
 262           ip_stripoptions(m, (struct mbuf *)0);
 263           iphlen=sizeof(struct ip );
 264         }
 265         /* XXX Check if too short */
 266
 267
 268         /*
 269          * Save a copy of the IP header in case we want restore it
 270          * for sending an ICMP error message in response.
 271          */
 272         ip=mtod(m, struct ip *);
 273         save_ip = *ip;
 274         save_ip.ip_len+= iphlen;
 275
 276         /*
 277          * Checksum extended TCP header and data.
 278          */
 279         tlen = ((struct ip *)ti)->ip_len;
 280         tcpiphdr2qlink(ti)->next = tcpiphdr2qlink(ti)->prev = NULL;
 281         memset(&ti->ti_i.ih_mbuf, 0 , sizeof(struct mbuf_ptr));
 282         ti->ti_x1 = 0;
 283         ti->ti_len = htons((uint16_t)tlen);
 284         len = sizeof(struct ip ) + tlen;
 285         if(cksum(m, len)) {
 286           goto drop;
 287         }
 288
 289         /*
 290          * Check that TCP offset makes sense,
 291          * pull out TCP options and adjust length.              XXX
 292          */
 293         off = ti->ti_off << 2;
 294         if (off < sizeof (struct tcphdr) || off > tlen) {
 295           goto drop;
 296         }
 297         tlen -= off;
 298         ti->ti_len = tlen;
 299         if (off > sizeof (struct tcphdr)) {
 300           optlen = off - sizeof (struct tcphdr);
 301           optp = mtod(m, caddr_t) + sizeof (struct tcpiphdr);
 302         }
 303         tiflags = ti->ti_flags;
 304
 305         /*
 306          * Convert TCP protocol specific fields to host format.
 307          */
 308         NTOHL(ti->ti_seq);
 309         NTOHL(ti->ti_ack);
 310         NTOHS(ti->ti_win);
 311         NTOHS(ti->ti_urp);
 312
 313         /*
 314          * Drop TCP, IP headers and TCP options.
 315          */
 316         m->m_data += sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
 317         m->m_len  -= sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
 318
 319     if (slirp->restricted) {
 320         for (ex_ptr = slirp->exec_list; ex_ptr; ex_ptr = ex_ptr->ex_next) {
 321             if (ex_ptr->ex_fport == ti->ti_dport &&
 322                 ti->ti_dst.s_addr == ex_ptr->ex_addr.s_addr) {
 323                 break;
 324             }
 325         }
 326         if (!ex_ptr)
 327             goto drop;
 328     }
 329         /*
 330          * Locate pcb for segment.
 331          */
 332 findso:
 333         so = slirp->tcp_last_so;
 334         if (so->so_fport != ti->ti_dport ||
 335             so->so_lport != ti->ti_sport ||
 336             so->so_laddr.s_addr != ti->ti_src.s_addr ||
 337             so->so_faddr.s_addr != ti->ti_dst.s_addr) {
 338                 so = solookup(&slirp->tcb, ti->ti_src, ti->ti_sport,
 339                                ti->ti_dst, ti->ti_dport);
 340                 if (so)
 341                         slirp->tcp_last_so = so;
 342         }
 343
 344         /*
 345          * If the state is CLOSED (i.e., TCB does not exist) then
 346          * all data in the incoming segment is discarded.
 347          * If the TCB exists but is in CLOSED state, it is embryonic,
 348          * but should either do a listen or a connect soon.
 349          *
 350          * state == CLOSED means we've done socreate() but haven't
 351          * attached it to a protocol yet...
 352          *
 353          * XXX If a TCB does not exist, and the TH_SYN flag is
 354          * the only flag set, then create a session, mark it
 355          * as if it was LISTENING, and continue...
 356          */
 357         if (so == NULL) {
 358           if ((tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) != TH_SYN)
 359             goto dropwithreset;
 360
 361           if ((so = socreate(slirp)) == NULL)
 362             goto dropwithreset;
 363           if (tcp_attach(so) < 0) {
 364             free(so); /* Not sofree (if it failed, it's not insqued) */
 365             goto dropwithreset;
 366           }
 367
 368           sbreserve(&so->so_snd, TCP_SNDSPACE);
 369           sbreserve(&so->so_rcv, TCP_RCVSPACE);
 370
 371           so->so_laddr = ti->ti_src;
 372           so->so_lport = ti->ti_sport;
 373           so->so_faddr = ti->ti_dst;
 374           so->so_fport = ti->ti_dport;
 375
 376           if ((so->so_iptos = tcp_tos(so)) == 0)
 377             so->so_iptos = ((struct ip *)ti)->ip_tos;
 378
 379           tp = sototcpcb(so);
 380           tp->t_state = TCPS_LISTEN;
 381         }
 382
 383         /*
 384          * If this is a still-connecting socket, this probably
 385          * a retransmit of the SYN.  Whether it's a retransmit SYN
 386          * or something else, we nuke it.
 387          */
 388         if (so->so_state & SS_ISFCONNECTING)
 389                 goto drop;
 390
 391         tp = sototcpcb(so);
 392
 393         /* XXX Should never fail */
 394         if (tp == NULL)
 395                 goto dropwithreset;
 396         if (tp->t_state == TCPS_CLOSED)
 397                 goto drop;
 398
 399         tiwin = ti->ti_win;
 400
 401         /*
 402          * Segment received on connection.
 403          * Reset idle time and keep-alive timer.
 404          */
 405         tp->t_idle = 0;
 406         if (SO_OPTIONS)
 407            tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL;
 408         else
 409            tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE;
 410
 411         /*
 412          * Process options if not in LISTEN state,
 413          * else do it below (after getting remote address).
 414          */
 415         if (optp && tp->t_state != TCPS_LISTEN)
 416                 tcp_dooptions(tp, (u_char *)optp, optlen, ti);
 417
 418         /*
 419          * Header prediction: check for the two common cases
 420          * of a uni-directional data xfer.  If the packet has
 421          * no control flags, is in-sequence, the window didn't
 422          * change and we're not retransmitting, it's a
 423          * candidate.  If the length is zero and the ack moved
 424          * forward, we're the sender side of the xfer.  Just
 425          * free the data acked & wake any higher level process
 426          * that was blocked waiting for space.  If the length
 427          * is non-zero and the ack didn't move, we're the
 428          * receiver side.  If we're getting packets in-order
 429          * (the reassembly queue is empty), add the data to
 430          * the socket buffer and note that we need a delayed ack.
 431          *
 432          * XXX Some of these tests are not needed
 433          * eg: the tiwin == tp->snd_wnd prevents many more
 434          * predictions.. with no *real* advantage..
 435          */
 436         if (tp->t_state == TCPS_ESTABLISHED &&
 437             (tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 438             ti->ti_seq == tp->rcv_nxt &&
 439             tiwin && tiwin == tp->snd_wnd &&
 440             tp->snd_nxt == tp->snd_max) {
 441                 if (ti->ti_len == 0) {
 442                         if (SEQ_GT(ti->ti_ack, tp->snd_una) &&
 443                             SEQ_LEQ(ti->ti_ack, tp->snd_max) &&
 444                             tp->snd_cwnd >= tp->snd_wnd) {
 445                                 /*
 446                                  * this is a pure ack for outstanding data.
 447                                  */
 448                                 if (tp->t_rtt &&
 449                                     SEQ_GT(ti->ti_ack, tp->t_rtseq))
 450                                         tcp_xmit_timer(tp, tp->t_rtt);
 451                                 acked = ti->ti_ack - tp->snd_una;
 452                                 sbdrop(&so->so_snd, acked);
 453                                 tp->snd_una = ti->ti_ack;
 454                                 m_freem(m);
 455
 456                                 /*
 457                                  * If all outstanding data are acked, stop
 458                                  * retransmit timer, otherwise restart timer
 459                                  * using current (possibly backed-off) value.
 460                                  * If process is waiting for space,
 461                                  * wakeup/selwakeup/signal.  If data
 462                                  * are ready to send, let tcp_output
 463                                  * decide between more output or persist.
 464                                  */
 465                                 if (tp->snd_una == tp->snd_max)
 466                                         tp->t_timer[TCPT_REXMT] = 0;
 467                                 else if (tp->t_timer[TCPT_PERSIST] == 0)
 468                                         tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
 469
 470                                 /*
 471                                  * This is called because sowwakeup might have
 472                                  * put data into so_snd.  Since we don't so sowwakeup,
 473                                  * we don't need this.. XXX???
 474                                  */
 475                                 if (so->so_snd.sb_cc)
 476                                         (void) tcp_output(tp);
 477
 478                                 return;
 479                         }
 480                 } else if (ti->ti_ack == tp->snd_una &&
 481                     tcpfrag_list_empty(tp) &&
 482                     ti->ti_len <= sbspace(&so->so_rcv)) {
 483                         /*
 484                          * this is a pure, in-sequence data packet
 485                          * with nothing on the reassembly queue and
 486                          * we have enough buffer space to take it.
 487                          */
 488                         tp->rcv_nxt += ti->ti_len;
 489                         /*
 490                          * Add data to socket buffer.
 491                          */
 492                         if (so->so_emu) {
 493                                 if (tcp_emu(so,m)) sbappend(so, m);
 494                         } else
 495                                 sbappend(so, m);
 496
 497                         /*
 498                          * If this is a short packet, then ACK now - with Nagel
 499                          *      congestion avoidance sender won't send more until
 500                          *      he gets an ACK.
 501                          *
 502                          * It is better to not delay acks at all to maximize
 503                          * TCP throughput.  See RFC 2581.
 504                          */
 505                         tp->t_flags |= TF_ACKNOW;
 506                         tcp_output(tp);
 507                         return;
 508                 }
 509         } /* header prediction */
 510         /*
 511          * Calculate amount of space in receive window,
 512          * and then do TCP input processing.
 513          * Receive window is amount of space in rcv queue,
 514          * but not less than advertised window.
 515          */
 516         { int win;
 517           win = sbspace(&so->so_rcv);
 518           if (win < 0)
 519             win = 0;
 520           tp->rcv_wnd = max(win, (int)(tp->rcv_adv - tp->rcv_nxt));
 521         }
 522
 523         switch (tp->t_state) {
 524
 525         /*
 526          * If the state is LISTEN then ignore segment if it contains an RST.
 527          * If the segment contains an ACK then it is bad and send a RST.
 528          * If it does not contain a SYN then it is not interesting; drop it.
 529          * Don't bother responding if the destination was a broadcast.
 530          * Otherwise initialize tp->rcv_nxt, and tp->irs, select an initial
 531          * tp->iss, and send a segment:
 532          *     <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
 533          * Also initialize tp->snd_nxt to tp->iss+1 and tp->snd_una to tp->iss.
 534          * Fill in remote peer address fields if not previously specified.
 535          * Enter SYN_RECEIVED state, and process any other fields of this
 536          * segment in this state.
 537          */
 538         case TCPS_LISTEN: {
 539
 540           if (tiflags & TH_RST)
 541             goto drop;
 542           if (tiflags & TH_ACK)
 543             goto dropwithreset;
 544           if ((tiflags & TH_SYN) == 0)
 545             goto drop;
 546
 547           /*
 548            * This has way too many gotos...
 549            * But a bit of spaghetti code never hurt anybody :)
 550            */
 551
 552           /*
 553            * If this is destined for the control address, then flag to
 554            * tcp_ctl once connected, otherwise connect
 555            */
 556           if ((so->so_faddr.s_addr & slirp->vnetwork_mask.s_addr) ==
 557               slirp->vnetwork_addr.s_addr) {
 558             if (so->so_faddr.s_addr != slirp->vhost_addr.s_addr &&
 559                 so->so_faddr.s_addr != slirp->vnameserver_addr.s_addr) {
 560                 /* May be an add exec */
 561                 for (ex_ptr = slirp->exec_list; ex_ptr;
 562                      ex_ptr = ex_ptr->ex_next) {
 563                   if(ex_ptr->ex_fport == so->so_fport &&
 564                      so->so_faddr.s_addr == ex_ptr->ex_addr.s_addr) {
 565                     so->so_state |= SS_CTL;
 566                     break;
 567                   }
 568                 }
 569                 if (so->so_state & SS_CTL) {
 570                     goto cont_input;
 571                 }
 572             }
 573             /* CTL_ALIAS: Do nothing, tcp_fconnect will be called on it */
 574           }
 575
 576           if (so->so_emu & EMU_NOCONNECT) {
 577             so->so_emu &= ~EMU_NOCONNECT;
 578             goto cont_input;
 579           }
 580
 581           if((tcp_fconnect(so) == -1) && (errno != EINPROGRESS) && (errno != EWOULDBLOCK)) {
 582             u_char code=ICMP_UNREACH_NET;
 583             DEBUG_MISC((dfd," tcp fconnect errno = %d-%s\n",
 584                         errno,strerror(errno)));
 585             if(errno == ECONNREFUSED) {
 586               /* ACK the SYN, send RST to refuse the connection */
 587               tcp_respond(tp, ti, m, ti->ti_seq+1, (tcp_seq)0,
 588                           TH_RST|TH_ACK);
 589             } else {
 590               if(errno == EHOSTUNREACH) code=ICMP_UNREACH_HOST;
 591               HTONL(ti->ti_seq);             /* restore tcp header */
 592               HTONL(ti->ti_ack);
 593               HTONS(ti->ti_win);
 594               HTONS(ti->ti_urp);
 595               m->m_data -= sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
 596               m->m_len  += sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
 597               *ip=save_ip;
 598               icmp_error(m, ICMP_UNREACH,code, 0,strerror(errno));
 599             }
 600             tcp_close(tp);
 601             m_free(m);
 602           } else {
 603             /*
 604              * Haven't connected yet, save the current mbuf
 605              * and ti, and return
 606              * XXX Some OS's don't tell us whether the connect()
 607              * succeeded or not.  So we must time it out.
 608              */
 609             so->so_m = m;
 610             so->so_ti = ti;
 611             tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
 612             tp->t_state = TCPS_SYN_RECEIVED;
 613           }
 614           return;
 615
 616         cont_conn:
 617           /* m==NULL
 618            * Check if the connect succeeded
 619            */
 620           if (so->so_state & SS_NOFDREF) {
 621             tp = tcp_close(tp);
 622             goto dropwithreset;
 623           }
 624         cont_input:
 625           tcp_template(tp);
 626
 627           if (optp)
 628             tcp_dooptions(tp, (u_char *)optp, optlen, ti);
 629
 630           if (iss)
 631             tp->iss = iss;
 632           else
 633             tp->iss = slirp->tcp_iss;
 634           slirp->tcp_iss += TCP_ISSINCR/2;
 635           tp->irs = ti->ti_seq;
 636           tcp_sendseqinit(tp);
 637           tcp_rcvseqinit(tp);
 638           tp->t_flags |= TF_ACKNOW;
 639           tp->t_state = TCPS_SYN_RECEIVED;
 640           tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
 641           goto trimthenstep6;
 642         } /* case TCPS_LISTEN */
 643
 644         /*
 645          * If the state is SYN_SENT:
 646          *      if seg contains an ACK, but not for our SYN, drop the input.
 647          *      if seg contains a RST, then drop the connection.
 648          *      if seg does not contain SYN, then drop it.
 649          * Otherwise this is an acceptable SYN segment
 650          *      initialize tp->rcv_nxt and tp->irs
 651          *      if seg contains ack then advance tp->snd_una
 652          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
 653          *      arrange for segment to be acked (eventually)
 654          *      continue processing rest of data/controls, beginning with URG
 655          */
 656         case TCPS_SYN_SENT:
 657                 if ((tiflags & TH_ACK) &&
 658                     (SEQ_LEQ(ti->ti_ack, tp->iss) ||
 659                      SEQ_GT(ti->ti_ack, tp->snd_max)))
 660                         goto dropwithreset;
 661
 662                 if (tiflags & TH_RST) {
 663                         if (tiflags & TH_ACK) {
 664                                 tcp_drop(tp, 0); /* XXX Check t_softerror! */
 665                         }
 666                         goto drop;
 667                 }
 668
 669                 if ((tiflags & TH_SYN) == 0)
 670                         goto drop;
 671                 if (tiflags & TH_ACK) {
 672                         tp->snd_una = ti->ti_ack;
 673                         if (SEQ_LT(tp->snd_nxt, tp->snd_una))
 674                                 tp->snd_nxt = tp->snd_una;
 675                 }
 676
 677                 tp->t_timer[TCPT_REXMT] = 0;
 678                 tp->irs = ti->ti_seq;
 679                 tcp_rcvseqinit(tp);
 680                 tp->t_flags |= TF_ACKNOW;
 681                 if (tiflags & TH_ACK && SEQ_GT(tp->snd_una, tp->iss)) {
 682                         soisfconnected(so);
 683                         tp->t_state = TCPS_ESTABLISHED;
 684
 685                         (void) tcp_reass(tp, (struct tcpiphdr *)0,
 686                                 (struct mbuf *)0);
 687                         /*
 688                          * if we didn't have to retransmit the SYN,
 689                          * use its rtt as our initial srtt & rtt var.
 690                          */
 691                         if (tp->t_rtt)
 692                                 tcp_xmit_timer(tp, tp->t_rtt);
 693                 } else
 694                         tp->t_state = TCPS_SYN_RECEIVED;
 695
 696 trimthenstep6:
 697                 /*
 698                  * Advance ti->ti_seq to correspond to first data byte.
 699                  * If data, trim to stay within window,
 700                  * dropping FIN if necessary.
 701                  */
 702                 ti->ti_seq++;
 703                 if (ti->ti_len > tp->rcv_wnd) {
 704                         todrop = ti->ti_len - tp->rcv_wnd;
 705                         m_adj(m, -todrop);
 706                         ti->ti_len = tp->rcv_wnd;
 707                         tiflags &= ~TH_FIN;
 708                 }
 709                 tp->snd_wl1 = ti->ti_seq - 1;
 710                 tp->rcv_up = ti->ti_seq;
 711                 goto step6;
 712         } /* switch tp->t_state */
 713         /*
 714          * States other than LISTEN or SYN_SENT.
 715          * Check that at least some bytes of segment are within
 716          * receive window.  If segment begins before rcv_nxt,
 717          * drop leading data (and SYN); if nothing left, just ack.
 718          */
 719         todrop = tp->rcv_nxt - ti->ti_seq;
 720         if (todrop > 0) {
 721                 if (tiflags & TH_SYN) {
 722                         tiflags &= ~TH_SYN;
 723                         ti->ti_seq++;
 724                         if (ti->ti_urp > 1)
 725                                 ti->ti_urp--;
 726                         else
 727                                 tiflags &= ~TH_URG;
 728                         todrop--;
 729                 }
 730                 /*
 731                  * Following if statement from Stevens, vol. 2, p. 960.
 732                  */
 733                 if (todrop > ti->ti_len
 734                     || (todrop == ti->ti_len && (tiflags & TH_FIN) == 0)) {
 735                         /*
 736                          * Any valid FIN must be to the left of the window.
 737                          * At this point the FIN must be a duplicate or out
 738                          * of sequence; drop it.
 739                          */
 740                         tiflags &= ~TH_FIN;
 741
 742                         /*
 743                          * Send an ACK to resynchronize and drop any data.
 744                          * But keep on processing for RST or ACK.
 745                          */
 746                         tp->t_flags |= TF_ACKNOW;
 747                         todrop = ti->ti_len;
 748                 }
 749                 m_adj(m, todrop);
 750                 ti->ti_seq += todrop;
 751                 ti->ti_len -= todrop;
 752                 if (ti->ti_urp > todrop)
 753                         ti->ti_urp -= todrop;
 754                 else {
 755                         tiflags &= ~TH_URG;
 756                         ti->ti_urp = 0;
 757                 }
 758         }
 759         /*
 760          * If new data are received on a connection after the
 761          * user processes are gone, then RST the other end.
 762          */
 763         if ((so->so_state & SS_NOFDREF) &&
 764             tp->t_state > TCPS_CLOSE_WAIT && ti->ti_len) {
 765                 tp = tcp_close(tp);
 766                 goto dropwithreset;
 767         }
 768
 769         /*
 770          * If segment ends after window, drop trailing data
 771          * (and PUSH and FIN); if nothing left, just ACK.
 772          */
 773         todrop = (ti->ti_seq+ti->ti_len) - (tp->rcv_nxt+tp->rcv_wnd);
 774         if (todrop > 0) {
 775                 if (todrop >= ti->ti_len) {
 776                         /*
 777                          * If a new connection request is received
 778                          * while in TIME_WAIT, drop the old connection
 779                          * and start over if the sequence numbers
 780                          * are above the previous ones.
 781                          */
 782                         if (tiflags & TH_SYN &&
 783                             tp->t_state == TCPS_TIME_WAIT &&
 784                             SEQ_GT(ti->ti_seq, tp->rcv_nxt)) {
 785                                 iss = tp->rcv_nxt + TCP_ISSINCR;
 786                                 tp = tcp_close(tp);
 787                                 goto findso;
 788                         }
 789                         /*
 790                          * If window is closed can only take segments at
 791                          * window edge, and have to drop data and PUSH from
 792                          * incoming segments.  Continue processing, but
 793                          * remember to ack.  Otherwise, drop segment
 794                          * and ack.
 795                          */
 796                         if (tp->rcv_wnd == 0 && ti->ti_seq == tp->rcv_nxt) {
 797                                 tp->t_flags |= TF_ACKNOW;
 798                         } else {
 799                                 goto dropafterack;
 800                         }
 801                 }
 802                 m_adj(m, -todrop);
 803                 ti->ti_len -= todrop;
 804                 tiflags &= ~(TH_PUSH|TH_FIN);
 805         }
 806
 807         /*
 808          * If the RST bit is set examine the state:
 809          *    SYN_RECEIVED STATE:
 810          *      If passive open, return to LISTEN state.
 811          *      If active open, inform user that connection was refused.
 812          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT2, CLOSE_WAIT STATES:
 813          *      Inform user that connection was reset, and close tcb.
 814          *    CLOSING, LAST_ACK, TIME_WAIT STATES
 815          *      Close the tcb.
 816          */
 817         if (tiflags&TH_RST) switch (tp->t_state) {
 818
 819         case TCPS_SYN_RECEIVED:
 820         case TCPS_ESTABLISHED:
 821         case TCPS_FIN_WAIT_1:
 822         case TCPS_FIN_WAIT_2:
 823         case TCPS_CLOSE_WAIT:
 824                 tp->t_state = TCPS_CLOSED;
 825                 tcp_close(tp);
 826                 goto drop;
 827
 828         case TCPS_CLOSING:
 829         case TCPS_LAST_ACK:
 830         case TCPS_TIME_WAIT:
 831                 tcp_close(tp);
 832                 goto drop;
 833         }
 834
 835         /*
 836          * If a SYN is in the window, then this is an
 837          * error and we send an RST and drop the connection.
 838          */
 839         if (tiflags & TH_SYN) {
 840                 tp = tcp_drop(tp,0);
 841                 goto dropwithreset;
 842         }
 843
 844         /*
 845          * If the ACK bit is off we drop the segment and return.
 846          */
 847         if ((tiflags & TH_ACK) == 0) goto drop;
 848
 849         /*
 850          * Ack processing.
 851          */
 852         switch (tp->t_state) {
 853         /*
 854          * In SYN_RECEIVED state if the ack ACKs our SYN then enter
 855          * ESTABLISHED state and continue processing, otherwise
 856          * send an RST.  una<=ack<=max
 857          */
 858         case TCPS_SYN_RECEIVED:
 859
 860                 if (SEQ_GT(tp->snd_una, ti->ti_ack) ||
 861                     SEQ_GT(ti->ti_ack, tp->snd_max))
 862                         goto dropwithreset;
 863                 tp->t_state = TCPS_ESTABLISHED;
 864                 /*
 865                  * The sent SYN is ack'ed with our sequence number +1
 866                  * The first data byte already in the buffer will get
 867                  * lost if no correction is made.  This is only needed for
 868                  * SS_CTL since the buffer is empty otherwise.
 869                  * tp->snd_una++; or:
 870                  */
 871                 tp->snd_una=ti->ti_ack;
 872                 if (so->so_state & SS_CTL) {
 873                   /* So tcp_ctl reports the right state */
 874                   ret = tcp_ctl(so);
 875                   if (ret == 1) {
 876                     soisfconnected(so);
 877                     so->so_state &= ~SS_CTL;   /* success XXX */
 878                   } else if (ret == 2) {
 879                     so->so_state &= SS_PERSISTENT_MASK;
 880                     so->so_state |= SS_NOFDREF; /* CTL_CMD */
 881                   } else {
 882                     needoutput = 1;
 883                     tp->t_state = TCPS_FIN_WAIT_1;
 884                   }
 885                 } else {
 886                   soisfconnected(so);
 887                 }
 888
 889                 (void) tcp_reass(tp, (struct tcpiphdr *)0, (struct mbuf *)0);
 890                 tp->snd_wl1 = ti->ti_seq - 1;
 891                 /* Avoid ack processing; snd_una==ti_ack  =>  dup ack */
 892                 goto synrx_to_est;
 893                 /* fall into ... */
 894
 895         /*
 896          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
 897          * ACKs.  If the ack is in the range
 898          *      tp->snd_una < ti->ti_ack <= tp->snd_max
 899          * then advance tp->snd_una to ti->ti_ack and drop
 900          * data from the retransmission queue.  If this ACK reflects
 901          * more up to date window information we update our window information.
 902          */
 903         case TCPS_ESTABLISHED:
 904         case TCPS_FIN_WAIT_1:
 905         case TCPS_FIN_WAIT_2:
 906         case TCPS_CLOSE_WAIT:
 907         case TCPS_CLOSING:
 908         case TCPS_LAST_ACK:
 909         case TCPS_TIME_WAIT:
 910
 911                 if (SEQ_LEQ(ti->ti_ack, tp->snd_una)) {
 912                         if (ti->ti_len == 0 && tiwin == tp->snd_wnd) {
 913                           DEBUG_MISC((dfd," dup ack  m = %lx  so = %lx \n",
 914                                       (long )m, (long )so));
 915                                 /*
 916                                  * If we have outstanding data (other than
 917                                  * a window probe), this is a completely
 918                                  * duplicate ack (ie, window info didn't
 919                                  * change), the ack is the biggest we've
 920                                  * seen and we've seen exactly our rexmt
 921                                  * threshold of them, assume a packet
 922                                  * has been dropped and retransmit it.
 923                                  * Kludge snd_nxt & the congestion
 924                                  * window so we send only this one
 925                                  * packet.
 926                                  *
 927                                  * We know we're losing at the current
 928                                  * window size so do congestion avoidance
 929                                  * (set ssthresh to half the current window
 930                                  * and pull our congestion window back to
 931                                  * the new ssthresh).
 932                                  *
 933                                  * Dup acks mean that packets have left the
 934                                  * network (they're now cached at the receiver)
 935                                  * so bump cwnd by the amount in the receiver
 936                                  * to keep a constant cwnd packets in the
 937                                  * network.
 938                                  */
 939                                 if (tp->t_timer[TCPT_REXMT] == 0 ||
 940                                     ti->ti_ack != tp->snd_una)
 941                                         tp->t_dupacks = 0;
 942                                 else if (++tp->t_dupacks == TCPREXMTTHRESH) {
 943                                         tcp_seq onxt = tp->snd_nxt;
 944                                         u_int win =
 945                                             min(tp->snd_wnd, tp->snd_cwnd) / 2 /
 946                                                 tp->t_maxseg;
 947
 948                                         if (win < 2)
 949                                                 win = 2;
 950                                         tp->snd_ssthresh = win * tp->t_maxseg;
 951                                         tp->t_timer[TCPT_REXMT] = 0;
 952                                         tp->t_rtt = 0;
 953                                         tp->snd_nxt = ti->ti_ack;
 954                                         tp->snd_cwnd = tp->t_maxseg;
 955                                         (void) tcp_output(tp);
 956                                         tp->snd_cwnd = tp->snd_ssthresh +
 957                                                tp->t_maxseg * tp->t_dupacks;
 958                                         if (SEQ_GT(onxt, tp->snd_nxt))
 959                                                 tp->snd_nxt = onxt;
 960                                         goto drop;
 961                                 } else if (tp->t_dupacks > TCPREXMTTHRESH) {
 962                                         tp->snd_cwnd += tp->t_maxseg;
 963                                         (void) tcp_output(tp);
 964                                         goto drop;
 965                                 }
 966                         } else
 967                                 tp->t_dupacks = 0;
 968                         break;
 969                 }
 970         synrx_to_est:
 971                 /*
 972                  * If the congestion window was inflated to account
 973                  * for the other side's cached packets, retract it.
 974                  */
 975                 if (tp->t_dupacks > TCPREXMTTHRESH &&
 976                     tp->snd_cwnd > tp->snd_ssthresh)
 977                         tp->snd_cwnd = tp->snd_ssthresh;
 978                 tp->t_dupacks = 0;
 979                 if (SEQ_GT(ti->ti_ack, tp->snd_max)) {
 980                         goto dropafterack;
 981                 }
 982                 acked = ti->ti_ack - tp->snd_una;
 983
 984                 /*
 985                  * If transmit timer is running and timed sequence
 986                  * number was acked, update smoothed round trip time.
 987                  * Since we now have an rtt measurement, cancel the
 988                  * timer backoff (cf., Phil Karn's retransmit alg.).
 989                  * Recompute the initial retransmit timer.
 990                  */
 991                 if (tp->t_rtt && SEQ_GT(ti->ti_ack, tp->t_rtseq))
 992                         tcp_xmit_timer(tp,tp->t_rtt);
 993
 994                 /*
 995                  * If all outstanding data is acked, stop retransmit
 996                  * timer and remember to restart (more output or persist).
 997                  * If there is more data to be acked, restart retransmit
 998                  * timer, using current (possibly backed-off) value.
 999                  */
1000                 if (ti->ti_ack == tp->snd_max) {
1001                         tp->t_timer[TCPT_REXMT] = 0;
1002                         needoutput = 1;
1003                 } else if (tp->t_timer[TCPT_PERSIST] == 0)
1004                         tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
1005                 /*
1006                  * When new data is acked, open the congestion window.
1007                  * If the window gives us less than ssthresh packets
1008                  * in flight, open exponentially (maxseg per packet).
1009                  * Otherwise open linearly: maxseg per window
1010                  * (maxseg^2 / cwnd per packet).
1011                  */
1012                 {
1013                   register u_int cw = tp->snd_cwnd;
1014                   register u_int incr = tp->t_maxseg;
1015
1016                   if (cw > tp->snd_ssthresh)
1017                     incr = incr * incr / cw;
1018                   tp->snd_cwnd = min(cw + incr, TCP_MAXWIN<<tp->snd_scale);
1019                 }
1020                 if (acked > so->so_snd.sb_cc) {
1021                         tp->snd_wnd -= so->so_snd.sb_cc;
1022                         sbdrop(&so->so_snd, (int )so->so_snd.sb_cc);
1023                         ourfinisacked = 1;
1024                 } else {
1025                         sbdrop(&so->so_snd, acked);
1026                         tp->snd_wnd -= acked;
1027                         ourfinisacked = 0;
1028                 }
1029                 tp->snd_una = ti->ti_ack;
1030                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
1031                         tp->snd_nxt = tp->snd_una;
1032
1033                 switch (tp->t_state) {
1034
1035                 /*
1036                  * In FIN_WAIT_1 STATE in addition to the processing
1037                  * for the ESTABLISHED state if our FIN is now acknowledged
1038                  * then enter FIN_WAIT_2.
1039                  */
1040                 case TCPS_FIN_WAIT_1:
1041                         if (ourfinisacked) {
1042                                 /*
1043                                  * If we can't receive any more
1044                                  * data, then closing user can proceed.
1045                                  * Starting the timer is contrary to the
1046                                  * specification, but if we don't get a FIN
1047                                  * we'll hang forever.
1048                                  */
1049                                 if (so->so_state & SS_FCANTRCVMORE) {
1050                                         tp->t_timer[TCPT_2MSL] = TCP_MAXIDLE;
1051                                 }
1052                                 tp->t_state = TCPS_FIN_WAIT_2;
1053                         }
1054                         break;
1055
1056                 /*
1057                  * In CLOSING STATE in addition to the processing for
1058                  * the ESTABLISHED state if the ACK acknowledges our FIN
1059                  * then enter the TIME-WAIT state, otherwise ignore
1060                  * the segment.
1061                  */
1062                 case TCPS_CLOSING:
1063                         if (ourfinisacked) {
1064                                 tp->t_state = TCPS_TIME_WAIT;
1065                                 tcp_canceltimers(tp);
1066                                 tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
1067                         }
1068                         break;
1069
1070                 /*
1071                  * In LAST_ACK, we may still be waiting for data to drain
1072                  * and/or to be acked, as well as for the ack of our FIN.
1073                  * If our FIN is now acknowledged, delete the TCB,
1074                  * enter the closed state and return.
1075                  */
1076                 case TCPS_LAST_ACK:
1077                         if (ourfinisacked) {
1078                                 tcp_close(tp);
1079                                 goto drop;
1080                         }
1081                         break;
1082
1083                 /*
1084                  * In TIME_WAIT state the only thing that should arrive
1085                  * is a retransmission of the remote FIN.  Acknowledge
1086                  * it and restart the finack timer.
1087                  */
1088                 case TCPS_TIME_WAIT:
1089                         tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
1090                         goto dropafterack;
1091                 }
1092         } /* switch(tp->t_state) */
1093
1094 step6:
1095         /*
1096          * Update window information.
1097          * Don't look at window if no ACK: TAC's send garbage on first SYN.
1098          */
1099         if ((tiflags & TH_ACK) &&
1100             (SEQ_LT(tp->snd_wl1, ti->ti_seq) ||
1101             (tp->snd_wl1 == ti->ti_seq && (SEQ_LT(tp->snd_wl2, ti->ti_ack) ||
1102             (tp->snd_wl2 == ti->ti_ack && tiwin > tp->snd_wnd))))) {
1103                 tp->snd_wnd = tiwin;
1104                 tp->snd_wl1 = ti->ti_seq;
1105                 tp->snd_wl2 = ti->ti_ack;
1106                 if (tp->snd_wnd > tp->max_sndwnd)
1107                         tp->max_sndwnd = tp->snd_wnd;
1108                 needoutput = 1;
1109         }
1110
1111         /*
1112          * Process segments with URG.
1113          */
1114         if ((tiflags & TH_URG) && ti->ti_urp &&
1115             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
1116                 /*
1117                  * This is a kludge, but if we receive and accept
1118                  * random urgent pointers, we'll crash in
1119                  * soreceive.  It's hard to imagine someone
1120                  * actually wanting to send this much urgent data.
1121                  */
1122                 if (ti->ti_urp + so->so_rcv.sb_cc > so->so_rcv.sb_datalen) {
1123                         ti->ti_urp = 0;
1124                         tiflags &= ~TH_URG;
1125                         goto dodata;
1126                 }
1127                 /*
1128                  * If this segment advances the known urgent pointer,
1129                  * then mark the data stream.  This should not happen
1130                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
1131                  * a FIN has been received from the remote side.
1132                  * In these states we ignore the URG.
1133                  *
1134                  * According to RFC961 (Assigned Protocols),
1135                  * the urgent pointer points to the last octet
1136                  * of urgent data.  We continue, however,
1137                  * to consider it to indicate the first octet
1138                  * of data past the urgent section as the original
1139                  * spec states (in one of two places).
1140                  */
1141                 if (SEQ_GT(ti->ti_seq+ti->ti_urp, tp->rcv_up)) {
1142                         tp->rcv_up = ti->ti_seq + ti->ti_urp;
1143                         so->so_urgc =  so->so_rcv.sb_cc +
1144                                 (tp->rcv_up - tp->rcv_nxt); /* -1; */
1145                         tp->rcv_up = ti->ti_seq + ti->ti_urp;
1146
1147                 }
1148         } else
1149                 /*
1150                  * If no out of band data is expected,
1151                  * pull receive urgent pointer along
1152                  * with the receive window.
1153                  */
1154                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
1155                         tp->rcv_up = tp->rcv_nxt;
1156 dodata:
1157
1158         /*
1159          * Process the segment text, merging it into the TCP sequencing queue,
1160          * and arranging for acknowledgment of receipt if necessary.
1161          * This process logically involves adjusting tp->rcv_wnd as data
1162          * is presented to the user (this happens in tcp_usrreq.c,
1163          * case PRU_RCVD).  If a FIN has already been received on this
1164          * connection then we just ignore the text.
1165          */
1166         if ((ti->ti_len || (tiflags&TH_FIN)) &&
1167             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
1168                 TCP_REASS(tp, ti, m, so, tiflags);
1169         } else {
1170                 m_free(m);
1171                 tiflags &= ~TH_FIN;
1172         }
1173
1174         /*
1175          * If FIN is received ACK the FIN and let the user know
1176          * that the connection is closing.
1177          */
1178         if (tiflags & TH_FIN) {
1179                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
1180                         /*
1181                          * If we receive a FIN we can't send more data,
1182                          * set it SS_FDRAIN
1183                          * Shutdown the socket if there is no rx data in the
1184                          * buffer.
1185                          * soread() is called on completion of shutdown() and
1186                          * will got to TCPS_LAST_ACK, and use tcp_output()
1187                          * to send the FIN.
1188                          */
1189                         sofwdrain(so);
1190
1191                         tp->t_flags |= TF_ACKNOW;
1192                         tp->rcv_nxt++;
1193                 }
1194                 switch (tp->t_state) {
1195
1196                 /*
1197                  * In SYN_RECEIVED and ESTABLISHED STATES
1198                  * enter the CLOSE_WAIT state.
1199                  */
1200                 case TCPS_SYN_RECEIVED:
1201                 case TCPS_ESTABLISHED:
1202                   if(so->so_emu == EMU_CTL)        /* no shutdown on socket */
1203                     tp->t_state = TCPS_LAST_ACK;
1204                   else
1205                     tp->t_state = TCPS_CLOSE_WAIT;
1206                   break;
1207
1208                 /*
1209                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
1210                  * enter the CLOSING state.
1211                  */
1212                 case TCPS_FIN_WAIT_1:
1213                         tp->t_state = TCPS_CLOSING;
1214                         break;
1215
1216                 /*
1217                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
1218                  * starting the time-wait timer, turning off the other
1219                  * standard timers.
1220                  */
1221                 case TCPS_FIN_WAIT_2:
1222                         tp->t_state = TCPS_TIME_WAIT;
1223                         tcp_canceltimers(tp);
1224                         tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
1225                         break;
1226
1227                 /*
1228                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
1229                  */
1230                 case TCPS_TIME_WAIT:
1231                         tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
1232                         break;
1233                 }
1234         }
1235
1236         /*
1237          * If this is a small packet, then ACK now - with Nagel
1238          *      congestion avoidance sender won't send more until
1239          *      he gets an ACK.
1240          *
1241          * See above.
1242          */
1243         if (ti->ti_len && (unsigned)ti->ti_len <= 5 &&
1244             ((struct tcpiphdr_2 *)ti)->first_char == (char)27) {
1245                 tp->t_flags |= TF_ACKNOW;
1246         }
1247
1248         /*
1249          * Return any desired output.
1250          */
1251         if (needoutput || (tp->t_flags & TF_ACKNOW)) {
1252                 (void) tcp_output(tp);
1253         }
1254         return;
1255
1256 dropafterack:
1257         /*
1258          * Generate an ACK dropping incoming segment if it occupies
1259          * sequence space, where the ACK reflects our state.
1260          */
1261         if (tiflags & TH_RST)
1262                 goto drop;
1263         m_freem(m);
1264         tp->t_flags |= TF_ACKNOW;
1265         (void) tcp_output(tp);
1266         return;
1267
1268 dropwithreset:
1269         /* reuses m if m!=NULL, m_free() unnecessary */
1270         if (tiflags & TH_ACK)
1271                 tcp_respond(tp, ti, m, (tcp_seq)0, ti->ti_ack, TH_RST);
1272         else {
1273                 if (tiflags & TH_SYN) ti->ti_len++;
1274                 tcp_respond(tp, ti, m, ti->ti_seq+ti->ti_len, (tcp_seq)0,
1275                     TH_RST|TH_ACK);
1276         }
1277
1278         return;
1279
1280 drop:
1281         /*
1282          * Drop space held by incoming segment and return.
1283          */
1284         m_free(m);
1285
1286         return;
1287 }
1288
1289 static void
1290 tcp_dooptions(struct tcpcb *tp, u_char *cp, int cnt, struct tcpiphdr *ti)
1291 {
1292         uint16_t mss;
1293         int opt, optlen;
1294
1295         DEBUG_CALL("tcp_dooptions");
1296         DEBUG_ARGS((dfd," tp = %lx  cnt=%i \n", (long )tp, cnt));
1297
1298         for (; cnt > 0; cnt -= optlen, cp += optlen) {
1299                 opt = cp[0];
1300                 if (opt == TCPOPT_EOL)
1301                         break;
1302                 if (opt == TCPOPT_NOP)
1303                         optlen = 1;
1304                 else {
1305                         optlen = cp[1];
1306                         if (optlen <= 0)
1307                                 break;
1308                 }
1309                 switch (opt) {
1310
1311                 default:
1312                         continue;
1313
1314                 case TCPOPT_MAXSEG:
1315                         if (optlen != TCPOLEN_MAXSEG)
1316                                 continue;
1317                         if (!(ti->ti_flags & TH_SYN))
1318                                 continue;
1319                         memcpy((char *) &mss, (char *) cp + 2, sizeof(mss));
1320                         NTOHS(mss);
1321                         (void) tcp_mss(tp, mss);        /* sets t_maxseg */
1322                         break;
1323                 }
1324         }
1325 }
1326
1327
1328 /*
1329  * Pull out of band byte out of a segment so
1330  * it doesn't appear in the user's data queue.
1331  * It is still reflected in the segment length for
1332  * sequencing purposes.
1333  */
1334
1335 #ifdef notdef
1336
1337 void
1338 tcp_pulloutofband(so, ti, m)
1339         struct socket *so;
1340         struct tcpiphdr *ti;
1341         register struct mbuf *m;
1342 {
1343         int cnt = ti->ti_urp - 1;
1344
1345         while (cnt >= 0) {
1346                 if (m->m_len > cnt) {
1347                         char *cp = mtod(m, caddr_t) + cnt;
1348                         struct tcpcb *tp = sototcpcb(so);
1349
1350                         tp->t_iobc = *cp;
1351                         tp->t_oobflags |= TCPOOB_HAVEDATA;
1352                         memcpy(sp, cp+1, (unsigned)(m->m_len - cnt - 1));
1353                         m->m_len--;
1354                         return;
1355                 }
1356                 cnt -= m->m_len;
1357                 m = m->m_next; /* XXX WRONG! Fix it! */
1358                 if (m == 0)
1359                         break;
1360         }
1361         panic("tcp_pulloutofband");
1362 }
1363
1364 #endif /* notdef */
1365
1366 /*
1367  * Collect new round-trip time estimate
1368  * and update averages and current timeout.
1369  */
1370
1371 static void
1372 tcp_xmit_timer(register struct tcpcb *tp, int rtt)
1373 {
1374         register short delta;
1375
1376         DEBUG_CALL("tcp_xmit_timer");
1377         DEBUG_ARG("tp = %lx", (long)tp);
1378         DEBUG_ARG("rtt = %d", rtt);
1379
1380         if (tp->t_srtt != 0) {
1381                 /*
1382                  * srtt is stored as fixed point with 3 bits after the
1383                  * binary point (i.e., scaled by 8).  The following magic
1384                  * is equivalent to the smoothing algorithm in rfc793 with
1385                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
1386                  * point).  Adjust rtt to origin 0.
1387                  */
1388                 delta = rtt - 1 - (tp->t_srtt >> TCP_RTT_SHIFT);
1389                 if ((tp->t_srtt += delta) <= 0)
1390                         tp->t_srtt = 1;
1391                 /*
1392                  * We accumulate a smoothed rtt variance (actually, a
1393                  * smoothed mean difference), then set the retransmit
1394                  * timer to smoothed rtt + 4 times the smoothed variance.
1395                  * rttvar is stored as fixed point with 2 bits after the
1396                  * binary point (scaled by 4).  The following is
1397                  * equivalent to rfc793 smoothing with an alpha of .75
1398                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
1399                  * rfc793's wired-in beta.
1400                  */
1401                 if (delta < 0)
1402                         delta = -delta;
1403                 delta -= (tp->t_rttvar >> TCP_RTTVAR_SHIFT);
1404                 if ((tp->t_rttvar += delta) <= 0)
1405                         tp->t_rttvar = 1;
1406         } else {
1407                 /*
1408                  * No rtt measurement yet - use the unsmoothed rtt.
1409                  * Set the variance to half the rtt (so our first
1410                  * retransmit happens at 3*rtt).
1411                  */
1412                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
1413                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
1414         }
1415         tp->t_rtt = 0;
1416         tp->t_rxtshift = 0;
1417
1418         /*
1419          * the retransmit should happen at rtt + 4 * rttvar.
1420          * Because of the way we do the smoothing, srtt and rttvar
1421          * will each average +1/2 tick of bias.  When we compute
1422          * the retransmit timer, we want 1/2 tick of rounding and
1423          * 1 extra tick because of +-1/2 tick uncertainty in the
1424          * firing of the timer.  The bias will give us exactly the
1425          * 1.5 tick we need.  But, because the bias is
1426          * statistical, we have to test that we don't drop below
1427          * the minimum feasible timer (which is 2 ticks).
1428          */
1429         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
1430             (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
1431
1432         /*
1433          * We received an ack for a packet that wasn't retransmitted;
1434          * it is probably safe to discard any error indications we've
1435          * received recently.  This isn't quite right, but close enough
1436          * for now (a route might have failed after we sent a segment,
1437          * and the return path might not be symmetrical).
1438          */
1439         tp->t_softerror = 0;
1440 }
1441
1442 /*
1443  * Determine a reasonable value for maxseg size.
1444  * If the route is known, check route for mtu.
1445  * If none, use an mss that can be handled on the outgoing
1446  * interface without forcing IP to fragment; if bigger than
1447  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
1448  * to utilize large mbufs.  If no route is found, route has no mtu,
1449  * or the destination isn't local, use a default, hopefully conservative
1450  * size (usually 512 or the default IP max size, but no more than the mtu
1451  * of the interface), as we can't discover anything about intervening
1452  * gateways or networks.  We also initialize the congestion/slow start
1453  * window to be a single segment if the destination isn't local.
1454  * While looking at the routing entry, we also initialize other path-dependent
1455  * parameters from pre-set or cached values in the routing entry.
1456  */
1457
1458 int
1459 tcp_mss(struct tcpcb *tp, u_int offer)
1460 {
1461         struct socket *so = tp->t_socket;
1462         int mss;
1463
1464         DEBUG_CALL("tcp_mss");
1465         DEBUG_ARG("tp = %lx", (long)tp);
1466         DEBUG_ARG("offer = %d", offer);
1467
1468         mss = min(IF_MTU, IF_MRU) - sizeof(struct tcpiphdr);
1469         if (offer)
1470                 mss = min(mss, offer);
1471         mss = max(mss, 32);
1472         if (mss < tp->t_maxseg || offer != 0)
1473            tp->t_maxseg = mss;
1474
1475         tp->snd_cwnd = mss;
1476
1477         sbreserve(&so->so_snd, TCP_SNDSPACE + ((TCP_SNDSPACE % mss) ?
1478                                                (mss - (TCP_SNDSPACE % mss)) :
1479                                                0));
1480         sbreserve(&so->so_rcv, TCP_RCVSPACE + ((TCP_RCVSPACE % mss) ?
1481                                                (mss - (TCP_RCVSPACE % mss)) :
1482                                                0));
1483
1484         DEBUG_MISC((dfd, " returning mss = %d\n", mss));
1485
1486         return mss;
1487 }