net/ipv6/netfilter/nf_reject_ipv6.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* (C) 1999-2001 Paul `Rusty' Russell
   3  * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   4  */
   5
   6 #include <linux/module.h>
   7 #include <net/ipv6.h>
   8 #include <net/ip6_route.h>
   9 #include <net/ip6_fib.h>
  10 #include <net/ip6_checksum.h>
  11 #include <net/netfilter/ipv6/nf_reject.h>
  12 #include <linux/netfilter_ipv6.h>
  13 #include <linux/netfilter_bridge.h>
  14
  15 static bool nf_reject_v6_csum_ok(struct sk_buff *skb, int hook)
  16 {
  17         const struct ipv6hdr *ip6h = ipv6_hdr(skb);
  18         int thoff;
  19         __be16 fo;
  20         u8 proto = ip6h->nexthdr;
  21
  22         if (skb_csum_unnecessary(skb))
  23                 return true;
  24
  25         if (ip6h->payload_len &&
  26             pskb_trim_rcsum(skb, ntohs(ip6h->payload_len) + sizeof(*ip6h)))
  27                 return false;
  28
  29         ip6h = ipv6_hdr(skb);
  30         thoff = ipv6_skip_exthdr(skb, ((u8*)(ip6h+1) - skb->data), &proto, &fo);
  31         if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
  32                 return false;
  33
  34         if (!nf_reject_verify_csum(skb, thoff, proto))
  35                 return true;
  36
  37         return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
  38 }
  39
  40 static int nf_reject_ip6hdr_validate(struct sk_buff *skb)
  41 {
  42         struct ipv6hdr *hdr;
  43         u32 pkt_len;
  44
  45         if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
  46                 return 0;
  47
  48         hdr = ipv6_hdr(skb);
  49         if (hdr->version != 6)
  50                 return 0;
  51
  52         pkt_len = ntohs(hdr->payload_len);
  53         if (pkt_len + sizeof(struct ipv6hdr) > skb->len)
  54                 return 0;
  55
  56         return 1;
  57 }
  58
  59 struct sk_buff *nf_reject_skb_v6_tcp_reset(struct net *net,
  60                                            struct sk_buff *oldskb,
  61                                            const struct net_device *dev,
  62                                            int hook)
  63 {
  64         struct sk_buff *nskb;
  65         const struct tcphdr *oth;
  66         struct tcphdr _oth;
  67         unsigned int otcplen;
  68         struct ipv6hdr *nip6h;
  69
  70         if (!nf_reject_ip6hdr_validate(oldskb))
  71                 return NULL;
  72
  73         oth = nf_reject_ip6_tcphdr_get(oldskb, &_oth, &otcplen, hook);
  74         if (!oth)
  75                 return NULL;
  76
  77         nskb = alloc_skb(sizeof(struct ipv6hdr) + sizeof(struct tcphdr) +
  78                          LL_MAX_HEADER, GFP_ATOMIC);
  79         if (!nskb)
  80                 return NULL;
  81
  82         nskb->dev = (struct net_device *)dev;
  83
  84         skb_reserve(nskb, LL_MAX_HEADER);
  85         nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP,
  86                                      net->ipv6.devconf_all->hop_limit);
  87         nf_reject_ip6_tcphdr_put(nskb, oldskb, oth, otcplen);
  88         nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));
  89
  90         return nskb;
  91 }
  92 EXPORT_SYMBOL_GPL(nf_reject_skb_v6_tcp_reset);
  93
  94 struct sk_buff *nf_reject_skb_v6_unreach(struct net *net,
  95                                          struct sk_buff *oldskb,
  96                                          const struct net_device *dev,
  97                                          int hook, u8 code)
  98 {
  99         struct sk_buff *nskb;
 100         struct ipv6hdr *nip6h;
 101         struct icmp6hdr *icmp6h;
 102         unsigned int len;
 103
 104         if (!nf_reject_ip6hdr_validate(oldskb))
 105                 return NULL;
 106
 107         /* Include "As much of invoking packet as possible without the ICMPv6
 108          * packet exceeding the minimum IPv6 MTU" in the ICMP payload.
 109          */
 110         len = min_t(unsigned int, 1220, oldskb->len);
 111
 112         if (!pskb_may_pull(oldskb, len))
 113                 return NULL;
 114
 115         if (!nf_reject_v6_csum_ok(oldskb, hook))
 116                 return NULL;
 117
 118         nskb = alloc_skb(sizeof(struct ipv6hdr) + sizeof(struct icmp6hdr) +
 119                          LL_MAX_HEADER + len, GFP_ATOMIC);
 120         if (!nskb)
 121                 return NULL;
 122
 123         nskb->dev = (struct net_device *)dev;
 124
 125         skb_reserve(nskb, LL_MAX_HEADER);
 126         nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_ICMPV6,
 127                                      net->ipv6.devconf_all->hop_limit);
 128
 129         skb_reset_transport_header(nskb);
 130         icmp6h = skb_put_zero(nskb, sizeof(struct icmp6hdr));
 131         icmp6h->icmp6_type = ICMPV6_DEST_UNREACH;
 132         icmp6h->icmp6_code = code;
 133
 134         skb_put_data(nskb, skb_network_header(oldskb), len);
 135         nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));
 136
 137         icmp6h->icmp6_cksum =
 138                 csum_ipv6_magic(&nip6h->saddr, &nip6h->daddr,
 139                                 nskb->len - sizeof(struct ipv6hdr),
 140                                 IPPROTO_ICMPV6,
 141                                 csum_partial(icmp6h,
 142                                              nskb->len - sizeof(struct ipv6hdr),
 143                                              0));
 144
 145         return nskb;
 146 }
 147 EXPORT_SYMBOL_GPL(nf_reject_skb_v6_unreach);
 148
 149 const struct tcphdr *nf_reject_ip6_tcphdr_get(struct sk_buff *oldskb,
 150                                               struct tcphdr *otcph,
 151                                               unsigned int *otcplen, int hook)
 152 {
 153         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
 154         u8 proto;
 155         __be16 frag_off;
 156         int tcphoff;
 157
 158         proto = oip6h->nexthdr;
 159         tcphoff = ipv6_skip_exthdr(oldskb, ((u8 *)(oip6h + 1) - oldskb->data),
 160                                    &proto, &frag_off);
 161
 162         if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
 163                 pr_debug("Cannot get TCP header.\n");
 164                 return NULL;
 165         }
 166
 167         *otcplen = oldskb->len - tcphoff;
 168
 169         /* IP header checks: fragment, too short. */
 170         if (proto != IPPROTO_TCP || *otcplen < sizeof(struct tcphdr)) {
 171                 pr_debug("proto(%d) != IPPROTO_TCP or too short (len = %d)\n",
 172                          proto, *otcplen);
 173                 return NULL;
 174         }
 175
 176         otcph = skb_header_pointer(oldskb, tcphoff, sizeof(struct tcphdr),
 177                                    otcph);
 178         if (otcph == NULL)
 179                 return NULL;
 180
 181         /* No RST for RST. */
 182         if (otcph->rst) {
 183                 pr_debug("RST is set\n");
 184                 return NULL;
 185         }
 186
 187         /* Check checksum. */
 188         if (nf_ip6_checksum(oldskb, hook, tcphoff, IPPROTO_TCP)) {
 189                 pr_debug("TCP checksum is invalid\n");
 190                 return NULL;
 191         }
 192
 193         return otcph;
 194 }
 195 EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_get);
 196
 197 struct ipv6hdr *nf_reject_ip6hdr_put(struct sk_buff *nskb,
 198                                      const struct sk_buff *oldskb,
 199                                      __u8 protocol, int hoplimit)
 200 {
 201         struct ipv6hdr *ip6h;
 202         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
 203 #define DEFAULT_TOS_VALUE       0x0U
 204         const __u8 tclass = DEFAULT_TOS_VALUE;
 205
 206         skb_put(nskb, sizeof(struct ipv6hdr));
 207         skb_reset_network_header(nskb);
 208         ip6h = ipv6_hdr(nskb);
 209         ip6_flow_hdr(ip6h, tclass, 0);
 210         ip6h->hop_limit = hoplimit;
 211         ip6h->nexthdr = protocol;
 212         ip6h->saddr = oip6h->daddr;
 213         ip6h->daddr = oip6h->saddr;
 214
 215         nskb->protocol = htons(ETH_P_IPV6);
 216
 217         return ip6h;
 218 }
 219 EXPORT_SYMBOL_GPL(nf_reject_ip6hdr_put);
 220
 221 void nf_reject_ip6_tcphdr_put(struct sk_buff *nskb,
 222                               const struct sk_buff *oldskb,
 223                               const struct tcphdr *oth, unsigned int otcplen)
 224 {
 225         struct tcphdr *tcph;
 226         int needs_ack;
 227
 228         skb_reset_transport_header(nskb);
 229         tcph = skb_put(nskb, sizeof(struct tcphdr));
 230         /* Truncate to length (no data) */
 231         tcph->doff = sizeof(struct tcphdr)/4;
 232         tcph->source = oth->dest;
 233         tcph->dest = oth->source;
 234
 235         if (oth->ack) {
 236                 needs_ack = 0;
 237                 tcph->seq = oth->ack_seq;
 238                 tcph->ack_seq = 0;
 239         } else {
 240                 needs_ack = 1;
 241                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
 242                                       otcplen - (oth->doff<<2));
 243                 tcph->seq = 0;
 244         }
 245
 246         /* Reset flags */
 247         ((u_int8_t *)tcph)[13] = 0;
 248         tcph->rst = 1;
 249         tcph->ack = needs_ack;
 250         tcph->window = 0;
 251         tcph->urg_ptr = 0;
 252         tcph->check = 0;
 253
 254         /* Adjust TCP checksum */
 255         tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
 256                                       &ipv6_hdr(nskb)->daddr,
 257                                       sizeof(struct tcphdr), IPPROTO_TCP,
 258                                       csum_partial(tcph,
 259                                                    sizeof(struct tcphdr), 0));
 260 }
 261 EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_put);
 262
 263 static int nf_reject6_fill_skb_dst(struct sk_buff *skb_in)
 264 {
 265         struct dst_entry *dst = NULL;
 266         struct flowi fl;
 267
 268         memset(&fl, 0, sizeof(struct flowi));
 269         fl.u.ip6.daddr = ipv6_hdr(skb_in)->saddr;
 270         nf_ip6_route(dev_net(skb_in->dev), &dst, &fl, false);
 271         if (!dst)
 272                 return -1;
 273
 274         skb_dst_set(skb_in, dst);
 275         return 0;
 276 }
 277
 278 void nf_send_reset6(struct net *net, struct sock *sk, struct sk_buff *oldskb,
 279                     int hook)
 280 {
 281         struct sk_buff *nskb;
 282         struct tcphdr _otcph;
 283         const struct tcphdr *otcph;
 284         unsigned int otcplen, hh_len;
 285         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
 286         struct ipv6hdr *ip6h;
 287         struct dst_entry *dst = NULL;
 288         struct flowi6 fl6;
 289
 290         if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
 291             (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
 292                 pr_debug("addr is not unicast.\n");
 293                 return;
 294         }
 295
 296         otcph = nf_reject_ip6_tcphdr_get(oldskb, &_otcph, &otcplen, hook);
 297         if (!otcph)
 298                 return;
 299
 300         memset(&fl6, 0, sizeof(fl6));
 301         fl6.flowi6_proto = IPPROTO_TCP;
 302         fl6.saddr = oip6h->daddr;
 303         fl6.daddr = oip6h->saddr;
 304         fl6.fl6_sport = otcph->dest;
 305         fl6.fl6_dport = otcph->source;
 306
 307         if (hook == NF_INET_PRE_ROUTING || hook == NF_INET_INGRESS) {
 308                 nf_ip6_route(net, &dst, flowi6_to_flowi(&fl6), false);
 309                 if (!dst)
 310                         return;
 311                 skb_dst_set(oldskb, dst);
 312         }
 313
 314         fl6.flowi6_oif = l3mdev_master_ifindex(skb_dst(oldskb)->dev);
 315         fl6.flowi6_mark = IP6_REPLY_MARK(net, oldskb->mark);
 316         security_skb_classify_flow(oldskb, flowi6_to_flowi_common(&fl6));
 317         dst = ip6_route_output(net, NULL, &fl6);
 318         if (dst->error) {
 319                 dst_release(dst);
 320                 return;
 321         }
 322         dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
 323         if (IS_ERR(dst))
 324                 return;
 325
 326         hh_len = (dst->dev->hard_header_len + 15)&~15;
 327         nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
 328                          + sizeof(struct tcphdr) + dst->trailer_len,
 329                          GFP_ATOMIC);
 330
 331         if (!nskb) {
 332                 net_dbg_ratelimited("cannot alloc skb\n");
 333                 dst_release(dst);
 334                 return;
 335         }
 336
 337         skb_dst_set(nskb, dst);
 338
 339         nskb->mark = fl6.flowi6_mark;
 340
 341         skb_reserve(nskb, hh_len + dst->header_len);
 342         ip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP,
 343                                     ip6_dst_hoplimit(dst));
 344         nf_reject_ip6_tcphdr_put(nskb, oldskb, otcph, otcplen);
 345
 346         nf_ct_attach(nskb, oldskb);
 347         nf_ct_set_closing(skb_nfct(oldskb));
 348
 349 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
 350         /* If we use ip6_local_out for bridged traffic, the MAC source on
 351          * the RST will be ours, instead of the destination's.  This confuses
 352          * some routers/firewalls, and they drop the packet.  So we need to
 353          * build the eth header using the original destination's MAC as the
 354          * source, and send the RST packet directly.
 355          */
 356         if (nf_bridge_info_exists(oldskb)) {
 357                 struct ethhdr *oeth = eth_hdr(oldskb);
 358                 struct net_device *br_indev;
 359
 360                 br_indev = nf_bridge_get_physindev(oldskb, net);
 361                 if (!br_indev) {
 362                         kfree_skb(nskb);
 363                         return;
 364                 }
 365
 366                 nskb->dev = br_indev;
 367                 nskb->protocol = htons(ETH_P_IPV6);
 368                 ip6h->payload_len = htons(sizeof(struct tcphdr));
 369                 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
 370                                     oeth->h_source, oeth->h_dest, nskb->len) < 0) {
 371                         kfree_skb(nskb);
 372                         return;
 373                 }
 374                 dev_queue_xmit(nskb);
 375         } else
 376 #endif
 377                 ip6_local_out(net, sk, nskb);
 378 }
 379 EXPORT_SYMBOL_GPL(nf_send_reset6);
 380
 381 static bool reject6_csum_ok(struct sk_buff *skb, int hook)
 382 {
 383         const struct ipv6hdr *ip6h = ipv6_hdr(skb);
 384         int thoff;
 385         __be16 fo;
 386         u8 proto;
 387
 388         if (skb_csum_unnecessary(skb))
 389                 return true;
 390
 391         proto = ip6h->nexthdr;
 392         thoff = ipv6_skip_exthdr(skb, ((u8 *)(ip6h + 1) - skb->data), &proto, &fo);
 393
 394         if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
 395                 return false;
 396
 397         if (!nf_reject_verify_csum(skb, thoff, proto))
 398                 return true;
 399
 400         return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
 401 }
 402
 403 void nf_send_unreach6(struct net *net, struct sk_buff *skb_in,
 404                       unsigned char code, unsigned int hooknum)
 405 {
 406         if (!reject6_csum_ok(skb_in, hooknum))
 407                 return;
 408
 409         if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
 410                 skb_in->dev = net->loopback_dev;
 411
 412         if ((hooknum == NF_INET_PRE_ROUTING || hooknum == NF_INET_INGRESS) &&
 413             nf_reject6_fill_skb_dst(skb_in) < 0)
 414                 return;
 415
 416         icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
 417 }
 418 EXPORT_SYMBOL_GPL(nf_send_unreach6);
 419
 420 MODULE_LICENSE("GPL");