net/ipv6/netfilter/ip6t_SYNPROXY.c

   1 /*
   2  * Copyright (c) 2013 Patrick McHardy <kaber@trash.net>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  */
   8
   9 #include <linux/module.h>
  10 #include <linux/skbuff.h>
  11 #include <net/ip6_checksum.h>
  12 #include <net/ip6_route.h>
  13 #include <net/tcp.h>
  14
  15 #include <linux/netfilter_ipv6/ip6_tables.h>
  16 #include <linux/netfilter/x_tables.h>
  17 #include <linux/netfilter/xt_SYNPROXY.h>
  18 #include <net/netfilter/nf_conntrack.h>
  19 #include <net/netfilter/nf_conntrack_seqadj.h>
  20 #include <net/netfilter/nf_conntrack_synproxy.h>
  21 #include <net/netfilter/nf_conntrack_ecache.h>
  22
  23 static struct ipv6hdr *
  24 synproxy_build_ip(struct net *net, struct sk_buff *skb,
  25                   const struct in6_addr *saddr,
  26                   const struct in6_addr *daddr)
  27 {
  28         struct ipv6hdr *iph;
  29
  30         skb_reset_network_header(skb);
  31         iph = skb_put(skb, sizeof(*iph));
  32         ip6_flow_hdr(iph, 0, 0);
  33         iph->hop_limit  = net->ipv6.devconf_all->hop_limit;
  34         iph->nexthdr    = IPPROTO_TCP;
  35         iph->saddr      = *saddr;
  36         iph->daddr      = *daddr;
  37
  38         return iph;
  39 }
  40
  41 static void
  42 synproxy_send_tcp(struct net *net,
  43                   const struct sk_buff *skb, struct sk_buff *nskb,
  44                   struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
  45                   struct ipv6hdr *niph, struct tcphdr *nth,
  46                   unsigned int tcp_hdr_size)
  47 {
  48         struct dst_entry *dst;
  49         struct flowi6 fl6;
  50
  51         nth->check = ~tcp_v6_check(tcp_hdr_size, &niph->saddr, &niph->daddr, 0);
  52         nskb->ip_summed   = CHECKSUM_PARTIAL;
  53         nskb->csum_start  = (unsigned char *)nth - nskb->head;
  54         nskb->csum_offset = offsetof(struct tcphdr, check);
  55
  56         memset(&fl6, 0, sizeof(fl6));
  57         fl6.flowi6_proto = IPPROTO_TCP;
  58         fl6.saddr = niph->saddr;
  59         fl6.daddr = niph->daddr;
  60         fl6.fl6_sport = nth->source;
  61         fl6.fl6_dport = nth->dest;
  62         security_skb_classify_flow((struct sk_buff *)skb, flowi6_to_flowi(&fl6));
  63         dst = ip6_route_output(net, NULL, &fl6);
  64         if (dst->error) {
  65                 dst_release(dst);
  66                 goto free_nskb;
  67         }
  68         dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
  69         if (IS_ERR(dst))
  70                 goto free_nskb;
  71
  72         skb_dst_set(nskb, dst);
  73
  74         if (nfct) {
  75                 nf_ct_set(nskb, (struct nf_conn *)nfct, ctinfo);
  76                 nf_conntrack_get(nfct);
  77         }
  78
  79         ip6_local_out(net, nskb->sk, nskb);
  80         return;
  81
  82 free_nskb:
  83         kfree_skb(nskb);
  84 }
  85
  86 static void
  87 synproxy_send_client_synack(struct net *net,
  88                             const struct sk_buff *skb, const struct tcphdr *th,
  89                             const struct synproxy_options *opts)
  90 {
  91         struct sk_buff *nskb;
  92         struct ipv6hdr *iph, *niph;
  93         struct tcphdr *nth;
  94         unsigned int tcp_hdr_size;
  95         u16 mss = opts->mss;
  96
  97         iph = ipv6_hdr(skb);
  98
  99         tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
 100         nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
 101                          GFP_ATOMIC);
 102         if (nskb == NULL)
 103                 return;
 104         skb_reserve(nskb, MAX_TCP_HEADER);
 105
 106         niph = synproxy_build_ip(net, nskb, &iph->daddr, &iph->saddr);
 107
 108         skb_reset_transport_header(nskb);
 109         nth = skb_put(nskb, tcp_hdr_size);
 110         nth->source     = th->dest;
 111         nth->dest       = th->source;
 112         nth->seq        = htonl(__cookie_v6_init_sequence(iph, th, &mss));
 113         nth->ack_seq    = htonl(ntohl(th->seq) + 1);
 114         tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
 115         if (opts->options & XT_SYNPROXY_OPT_ECN)
 116                 tcp_flag_word(nth) |= TCP_FLAG_ECE;
 117         nth->doff       = tcp_hdr_size / 4;
 118         nth->window     = 0;
 119         nth->check      = 0;
 120         nth->urg_ptr    = 0;
 121
 122         synproxy_build_options(nth, opts);
 123
 124         synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
 125                           IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
 126 }
 127
 128 static void
 129 synproxy_send_server_syn(struct net *net,
 130                          const struct sk_buff *skb, const struct tcphdr *th,
 131                          const struct synproxy_options *opts, u32 recv_seq)
 132 {
 133         struct synproxy_net *snet = synproxy_pernet(net);
 134         struct sk_buff *nskb;
 135         struct ipv6hdr *iph, *niph;
 136         struct tcphdr *nth;
 137         unsigned int tcp_hdr_size;
 138
 139         iph = ipv6_hdr(skb);
 140
 141         tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
 142         nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
 143                          GFP_ATOMIC);
 144         if (nskb == NULL)
 145                 return;
 146         skb_reserve(nskb, MAX_TCP_HEADER);
 147
 148         niph = synproxy_build_ip(net, nskb, &iph->saddr, &iph->daddr);
 149
 150         skb_reset_transport_header(nskb);
 151         nth = skb_put(nskb, tcp_hdr_size);
 152         nth->source     = th->source;
 153         nth->dest       = th->dest;
 154         nth->seq        = htonl(recv_seq - 1);
 155         /* ack_seq is used to relay our ISN to the synproxy hook to initialize
 156          * sequence number translation once a connection tracking entry exists.
 157          */
 158         nth->ack_seq    = htonl(ntohl(th->ack_seq) - 1);
 159         tcp_flag_word(nth) = TCP_FLAG_SYN;
 160         if (opts->options & XT_SYNPROXY_OPT_ECN)
 161                 tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
 162         nth->doff       = tcp_hdr_size / 4;
 163         nth->window     = th->window;
 164         nth->check      = 0;
 165         nth->urg_ptr    = 0;
 166
 167         synproxy_build_options(nth, opts);
 168
 169         synproxy_send_tcp(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
 170                           niph, nth, tcp_hdr_size);
 171 }
 172
 173 static void
 174 synproxy_send_server_ack(struct net *net,
 175                          const struct ip_ct_tcp *state,
 176                          const struct sk_buff *skb, const struct tcphdr *th,
 177                          const struct synproxy_options *opts)
 178 {
 179         struct sk_buff *nskb;
 180         struct ipv6hdr *iph, *niph;
 181         struct tcphdr *nth;
 182         unsigned int tcp_hdr_size;
 183
 184         iph = ipv6_hdr(skb);
 185
 186         tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
 187         nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
 188                          GFP_ATOMIC);
 189         if (nskb == NULL)
 190                 return;
 191         skb_reserve(nskb, MAX_TCP_HEADER);
 192
 193         niph = synproxy_build_ip(net, nskb, &iph->daddr, &iph->saddr);
 194
 195         skb_reset_transport_header(nskb);
 196         nth = skb_put(nskb, tcp_hdr_size);
 197         nth->source     = th->dest;
 198         nth->dest       = th->source;
 199         nth->seq        = htonl(ntohl(th->ack_seq));
 200         nth->ack_seq    = htonl(ntohl(th->seq) + 1);
 201         tcp_flag_word(nth) = TCP_FLAG_ACK;
 202         nth->doff       = tcp_hdr_size / 4;
 203         nth->window     = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
 204         nth->check      = 0;
 205         nth->urg_ptr    = 0;
 206
 207         synproxy_build_options(nth, opts);
 208
 209         synproxy_send_tcp(net, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
 210 }
 211
 212 static void
 213 synproxy_send_client_ack(struct net *net,
 214                          const struct sk_buff *skb, const struct tcphdr *th,
 215                          const struct synproxy_options *opts)
 216 {
 217         struct sk_buff *nskb;
 218         struct ipv6hdr *iph, *niph;
 219         struct tcphdr *nth;
 220         unsigned int tcp_hdr_size;
 221
 222         iph = ipv6_hdr(skb);
 223
 224         tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
 225         nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
 226                          GFP_ATOMIC);
 227         if (nskb == NULL)
 228                 return;
 229         skb_reserve(nskb, MAX_TCP_HEADER);
 230
 231         niph = synproxy_build_ip(net, nskb, &iph->saddr, &iph->daddr);
 232
 233         skb_reset_transport_header(nskb);
 234         nth = skb_put(nskb, tcp_hdr_size);
 235         nth->source     = th->source;
 236         nth->dest       = th->dest;
 237         nth->seq        = htonl(ntohl(th->seq) + 1);
 238         nth->ack_seq    = th->ack_seq;
 239         tcp_flag_word(nth) = TCP_FLAG_ACK;
 240         nth->doff       = tcp_hdr_size / 4;
 241         nth->window     = htons(ntohs(th->window) >> opts->wscale);
 242         nth->check      = 0;
 243         nth->urg_ptr    = 0;
 244
 245         synproxy_build_options(nth, opts);
 246
 247         synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
 248                           IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
 249 }
 250
 251 static bool
 252 synproxy_recv_client_ack(struct net *net,
 253                          const struct sk_buff *skb, const struct tcphdr *th,
 254                          struct synproxy_options *opts, u32 recv_seq)
 255 {
 256         struct synproxy_net *snet = synproxy_pernet(net);
 257         int mss;
 258
 259         mss = __cookie_v6_check(ipv6_hdr(skb), th, ntohl(th->ack_seq) - 1);
 260         if (mss == 0) {
 261                 this_cpu_inc(snet->stats->cookie_invalid);
 262                 return false;
 263         }
 264
 265         this_cpu_inc(snet->stats->cookie_valid);
 266         opts->mss = mss;
 267         opts->options |= XT_SYNPROXY_OPT_MSS;
 268
 269         if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
 270                 synproxy_check_timestamp_cookie(opts);
 271
 272         synproxy_send_server_syn(net, skb, th, opts, recv_seq);
 273         return true;
 274 }
 275
 276 static unsigned int
 277 synproxy_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 278 {
 279         const struct xt_synproxy_info *info = par->targinfo;
 280         struct net *net = xt_net(par);
 281         struct synproxy_net *snet = synproxy_pernet(net);
 282         struct synproxy_options opts = {};
 283         struct tcphdr *th, _th;
 284
 285         if (nf_ip6_checksum(skb, xt_hooknum(par), par->thoff, IPPROTO_TCP))
 286                 return NF_DROP;
 287
 288         th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
 289         if (th == NULL)
 290                 return NF_DROP;
 291
 292         if (!synproxy_parse_options(skb, par->thoff, th, &opts))
 293                 return NF_DROP;
 294
 295         if (th->syn && !(th->ack || th->fin || th->rst)) {
 296                 /* Initial SYN from client */
 297                 this_cpu_inc(snet->stats->syn_received);
 298
 299                 if (th->ece && th->cwr)
 300                         opts.options |= XT_SYNPROXY_OPT_ECN;
 301
 302                 opts.options &= info->options;
 303                 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
 304                         synproxy_init_timestamp_cookie(info, &opts);
 305                 else
 306                         opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
 307                                           XT_SYNPROXY_OPT_SACK_PERM |
 308                                           XT_SYNPROXY_OPT_ECN);
 309
 310                 synproxy_send_client_synack(net, skb, th, &opts);
 311                 consume_skb(skb);
 312                 return NF_STOLEN;
 313
 314         } else if (th->ack && !(th->fin || th->rst || th->syn)) {
 315                 /* ACK from client */
 316                 if (synproxy_recv_client_ack(net, skb, th, &opts, ntohl(th->seq))) {
 317                         consume_skb(skb);
 318                         return NF_STOLEN;
 319                 } else {
 320                         return NF_DROP;
 321                 }
 322         }
 323
 324         return XT_CONTINUE;
 325 }
 326
 327 static unsigned int ipv6_synproxy_hook(void *priv,
 328                                        struct sk_buff *skb,
 329                                        const struct nf_hook_state *nhs)
 330 {
 331         struct net *net = nhs->net;
 332         struct synproxy_net *snet = synproxy_pernet(net);
 333         enum ip_conntrack_info ctinfo;
 334         struct nf_conn *ct;
 335         struct nf_conn_synproxy *synproxy;
 336         struct synproxy_options opts = {};
 337         const struct ip_ct_tcp *state;
 338         struct tcphdr *th, _th;
 339         __be16 frag_off;
 340         u8 nexthdr;
 341         int thoff;
 342
 343         ct = nf_ct_get(skb, &ctinfo);
 344         if (ct == NULL)
 345                 return NF_ACCEPT;
 346
 347         synproxy = nfct_synproxy(ct);
 348         if (synproxy == NULL)
 349                 return NF_ACCEPT;
 350
 351         if (nf_is_loopback_packet(skb))
 352                 return NF_ACCEPT;
 353
 354         nexthdr = ipv6_hdr(skb)->nexthdr;
 355         thoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
 356                                  &frag_off);
 357         if (thoff < 0 || nexthdr != IPPROTO_TCP)
 358                 return NF_ACCEPT;
 359
 360         th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
 361         if (th == NULL)
 362                 return NF_DROP;
 363
 364         state = &ct->proto.tcp;
 365         switch (state->state) {
 366         case TCP_CONNTRACK_CLOSE:
 367                 if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
 368                         nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
 369                                                       ntohl(th->seq) + 1);
 370                         break;
 371                 }
 372
 373                 if (!th->syn || th->ack ||
 374                     CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
 375                         break;
 376
 377                 /* Reopened connection - reset the sequence number and timestamp
 378                  * adjustments, they will get initialized once the connection is
 379                  * reestablished.
 380                  */
 381                 nf_ct_seqadj_init(ct, ctinfo, 0);
 382                 synproxy->tsoff = 0;
 383                 this_cpu_inc(snet->stats->conn_reopened);
 384
 385                 /* fall through */
 386         case TCP_CONNTRACK_SYN_SENT:
 387                 if (!synproxy_parse_options(skb, thoff, th, &opts))
 388                         return NF_DROP;
 389
 390                 if (!th->syn && th->ack &&
 391                     CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
 392                         /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
 393                          * therefore we need to add 1 to make the SYN sequence
 394                          * number match the one of first SYN.
 395                          */
 396                         if (synproxy_recv_client_ack(net, skb, th, &opts,
 397                                                      ntohl(th->seq) + 1)) {
 398                                 this_cpu_inc(snet->stats->cookie_retrans);
 399                                 consume_skb(skb);
 400                                 return NF_STOLEN;
 401                         } else {
 402                                 return NF_DROP;
 403                         }
 404                 }
 405
 406                 synproxy->isn = ntohl(th->ack_seq);
 407                 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
 408                         synproxy->its = opts.tsecr;
 409
 410                 nf_conntrack_event_cache(IPCT_SYNPROXY, ct);
 411                 break;
 412         case TCP_CONNTRACK_SYN_RECV:
 413                 if (!th->syn || !th->ack)
 414                         break;
 415
 416                 if (!synproxy_parse_options(skb, thoff, th, &opts))
 417                         return NF_DROP;
 418
 419                 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) {
 420                         synproxy->tsoff = opts.tsval - synproxy->its;
 421                         nf_conntrack_event_cache(IPCT_SYNPROXY, ct);
 422                 }
 423
 424                 opts.options &= ~(XT_SYNPROXY_OPT_MSS |
 425                                   XT_SYNPROXY_OPT_WSCALE |
 426                                   XT_SYNPROXY_OPT_SACK_PERM);
 427
 428                 swap(opts.tsval, opts.tsecr);
 429                 synproxy_send_server_ack(net, state, skb, th, &opts);
 430
 431                 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
 432                 nf_conntrack_event_cache(IPCT_SEQADJ, ct);
 433
 434                 swap(opts.tsval, opts.tsecr);
 435                 synproxy_send_client_ack(net, skb, th, &opts);
 436
 437                 consume_skb(skb);
 438                 return NF_STOLEN;
 439         default:
 440                 break;
 441         }
 442
 443         synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
 444         return NF_ACCEPT;
 445 }
 446
 447 static const struct nf_hook_ops ipv6_synproxy_ops[] = {
 448         {
 449                 .hook           = ipv6_synproxy_hook,
 450                 .pf             = NFPROTO_IPV6,
 451                 .hooknum        = NF_INET_LOCAL_IN,
 452                 .priority       = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
 453         },
 454         {
 455                 .hook           = ipv6_synproxy_hook,
 456                 .pf             = NFPROTO_IPV6,
 457                 .hooknum        = NF_INET_POST_ROUTING,
 458                 .priority       = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
 459         },
 460 };
 461
 462 static int synproxy_tg6_check(const struct xt_tgchk_param *par)
 463 {
 464         struct synproxy_net *snet = synproxy_pernet(par->net);
 465         const struct ip6t_entry *e = par->entryinfo;
 466         int err;
 467
 468         if (!(e->ipv6.flags & IP6T_F_PROTO) ||
 469             e->ipv6.proto != IPPROTO_TCP ||
 470             e->ipv6.invflags & XT_INV_PROTO)
 471                 return -EINVAL;
 472
 473         err = nf_ct_netns_get(par->net, par->family);
 474         if (err)
 475                 return err;
 476
 477         if (snet->hook_ref6 == 0) {
 478                 err = nf_register_net_hooks(par->net, ipv6_synproxy_ops,
 479                                             ARRAY_SIZE(ipv6_synproxy_ops));
 480                 if (err) {
 481                         nf_ct_netns_put(par->net, par->family);
 482                         return err;
 483                 }
 484         }
 485
 486         snet->hook_ref6++;
 487         return err;
 488 }
 489
 490 static void synproxy_tg6_destroy(const struct xt_tgdtor_param *par)
 491 {
 492         struct synproxy_net *snet = synproxy_pernet(par->net);
 493
 494         snet->hook_ref6--;
 495         if (snet->hook_ref6 == 0)
 496                 nf_unregister_net_hooks(par->net, ipv6_synproxy_ops,
 497                                         ARRAY_SIZE(ipv6_synproxy_ops));
 498         nf_ct_netns_put(par->net, par->family);
 499 }
 500
 501 static struct xt_target synproxy_tg6_reg __read_mostly = {
 502         .name           = "SYNPROXY",
 503         .family         = NFPROTO_IPV6,
 504         .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
 505         .target         = synproxy_tg6,
 506         .targetsize     = sizeof(struct xt_synproxy_info),
 507         .checkentry     = synproxy_tg6_check,
 508         .destroy        = synproxy_tg6_destroy,
 509         .me             = THIS_MODULE,
 510 };
 511
 512 static int __init synproxy_tg6_init(void)
 513 {
 514         return xt_register_target(&synproxy_tg6_reg);
 515 }
 516
 517 static void __exit synproxy_tg6_exit(void)
 518 {
 519         xt_unregister_target(&synproxy_tg6_reg);
 520 }
 521
 522 module_init(synproxy_tg6_init);
 523 module_exit(synproxy_tg6_exit);
 524
 525 MODULE_LICENSE("GPL");
 526 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");