kernel/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
  22 static struct ipv6hdr *
  23 synproxy_build_ip(struct sk_buff *skb, const struct in6_addr *saddr,
  24                                        const struct in6_addr *daddr)
  25 {
  26         struct ipv6hdr *iph;
  27
  28         skb_reset_network_header(skb);
  29         iph = (struct ipv6hdr *)skb_put(skb, sizeof(*iph));
  30         ip6_flow_hdr(iph, 0, 0);
  31         iph->hop_limit  = 64;   //XXX
  32         iph->nexthdr    = IPPROTO_TCP;
  33         iph->saddr      = *saddr;
  34         iph->daddr      = *daddr;
  35
  36         return iph;
  37 }
  38
  39 static void
  40 synproxy_send_tcp(const struct synproxy_net *snet,
  41                   const struct sk_buff *skb, struct sk_buff *nskb,
  42                   struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
  43                   struct ipv6hdr *niph, struct tcphdr *nth,
  44                   unsigned int tcp_hdr_size)
  45 {
  46         struct net *net = nf_ct_net(snet->tmpl);
  47         struct dst_entry *dst;
  48         struct flowi6 fl6;
  49
  50         nth->check = ~tcp_v6_check(tcp_hdr_size, &niph->saddr, &niph->daddr, 0);
  51         nskb->ip_summed   = CHECKSUM_PARTIAL;
  52         nskb->csum_start  = (unsigned char *)nth - nskb->head;
  53         nskb->csum_offset = offsetof(struct tcphdr, check);
  54
  55         memset(&fl6, 0, sizeof(fl6));
  56         fl6.flowi6_proto = IPPROTO_TCP;
  57         fl6.saddr = niph->saddr;
  58         fl6.daddr = niph->daddr;
  59         fl6.fl6_sport = nth->source;
  60         fl6.fl6_dport = nth->dest;
  61         security_skb_classify_flow((struct sk_buff *)skb, flowi6_to_flowi(&fl6));
  62         dst = ip6_route_output(net, NULL, &fl6);
  63         if (dst == NULL || dst->error) {
  64                 dst_release(dst);
  65                 goto free_nskb;
  66         }
  67         dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
  68         if (IS_ERR(dst))
  69                 goto free_nskb;
  70
  71         skb_dst_set(nskb, dst);
  72
  73         if (nfct) {
  74                 nskb->nfct = nfct;
  75                 nskb->nfctinfo = 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(const struct synproxy_net *snet,
  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(nskb, &iph->daddr, &iph->saddr);
 107
 108         skb_reset_transport_header(nskb);
 109         nth = (struct tcphdr *)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(snet, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
 125                           niph, nth, tcp_hdr_size);
 126 }
 127
 128 static void
 129 synproxy_send_server_syn(const struct synproxy_net *snet,
 130                          const struct sk_buff *skb, const struct tcphdr *th,
 131                          const struct synproxy_options *opts, u32 recv_seq)
 132 {
 133         struct sk_buff *nskb;
 134         struct ipv6hdr *iph, *niph;
 135         struct tcphdr *nth;
 136         unsigned int tcp_hdr_size;
 137
 138         iph = ipv6_hdr(skb);
 139
 140         tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
 141         nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
 142                          GFP_ATOMIC);
 143         if (nskb == NULL)
 144                 return;
 145         skb_reserve(nskb, MAX_TCP_HEADER);
 146
 147         niph = synproxy_build_ip(nskb, &iph->saddr, &iph->daddr);
 148
 149         skb_reset_transport_header(nskb);
 150         nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
 151         nth->source     = th->source;
 152         nth->dest       = th->dest;
 153         nth->seq        = htonl(recv_seq - 1);
 154         /* ack_seq is used to relay our ISN to the synproxy hook to initialize
 155          * sequence number translation once a connection tracking entry exists.
 156          */
 157         nth->ack_seq    = htonl(ntohl(th->ack_seq) - 1);
 158         tcp_flag_word(nth) = TCP_FLAG_SYN;
 159         if (opts->options & XT_SYNPROXY_OPT_ECN)
 160                 tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
 161         nth->doff       = tcp_hdr_size / 4;
 162         nth->window     = th->window;
 163         nth->check      = 0;
 164         nth->urg_ptr    = 0;
 165
 166         synproxy_build_options(nth, opts);
 167
 168         synproxy_send_tcp(snet, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
 169                           niph, nth, tcp_hdr_size);
 170 }
 171
 172 static void
 173 synproxy_send_server_ack(const struct synproxy_net *snet,
 174                          const struct ip_ct_tcp *state,
 175                          const struct sk_buff *skb, const struct tcphdr *th,
 176                          const struct synproxy_options *opts)
 177 {
 178         struct sk_buff *nskb;
 179         struct ipv6hdr *iph, *niph;
 180         struct tcphdr *nth;
 181         unsigned int tcp_hdr_size;
 182
 183         iph = ipv6_hdr(skb);
 184
 185         tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
 186         nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
 187                          GFP_ATOMIC);
 188         if (nskb == NULL)
 189                 return;
 190         skb_reserve(nskb, MAX_TCP_HEADER);
 191
 192         niph = synproxy_build_ip(nskb, &iph->daddr, &iph->saddr);
 193
 194         skb_reset_transport_header(nskb);
 195         nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
 196         nth->source     = th->dest;
 197         nth->dest       = th->source;
 198         nth->seq        = htonl(ntohl(th->ack_seq));
 199         nth->ack_seq    = htonl(ntohl(th->seq) + 1);
 200         tcp_flag_word(nth) = TCP_FLAG_ACK;
 201         nth->doff       = tcp_hdr_size / 4;
 202         nth->window     = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
 203         nth->check      = 0;
 204         nth->urg_ptr    = 0;
 205
 206         synproxy_build_options(nth, opts);
 207
 208         synproxy_send_tcp(snet, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
 209 }
 210
 211 static void
 212 synproxy_send_client_ack(const struct synproxy_net *snet,
 213                          const struct sk_buff *skb, const struct tcphdr *th,
 214                          const struct synproxy_options *opts)
 215 {
 216         struct sk_buff *nskb;
 217         struct ipv6hdr *iph, *niph;
 218         struct tcphdr *nth;
 219         unsigned int tcp_hdr_size;
 220
 221         iph = ipv6_hdr(skb);
 222
 223         tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
 224         nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
 225                          GFP_ATOMIC);
 226         if (nskb == NULL)
 227                 return;
 228         skb_reserve(nskb, MAX_TCP_HEADER);
 229
 230         niph = synproxy_build_ip(nskb, &iph->saddr, &iph->daddr);
 231
 232         skb_reset_transport_header(nskb);
 233         nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
 234         nth->source     = th->source;
 235         nth->dest       = th->dest;
 236         nth->seq        = htonl(ntohl(th->seq) + 1);
 237         nth->ack_seq    = th->ack_seq;
 238         tcp_flag_word(nth) = TCP_FLAG_ACK;
 239         nth->doff       = tcp_hdr_size / 4;
 240         nth->window     = htons(ntohs(th->window) >> opts->wscale);
 241         nth->check      = 0;
 242         nth->urg_ptr    = 0;
 243
 244         synproxy_build_options(nth, opts);
 245
 246         synproxy_send_tcp(snet, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
 247                           niph, nth, tcp_hdr_size);
 248 }
 249
 250 static bool
 251 synproxy_recv_client_ack(const struct synproxy_net *snet,
 252                          const struct sk_buff *skb, const struct tcphdr *th,
 253                          struct synproxy_options *opts, u32 recv_seq)
 254 {
 255         int mss;
 256
 257         mss = __cookie_v6_check(ipv6_hdr(skb), th, ntohl(th->ack_seq) - 1);
 258         if (mss == 0) {
 259                 this_cpu_inc(snet->stats->cookie_invalid);
 260                 return false;
 261         }
 262
 263         this_cpu_inc(snet->stats->cookie_valid);
 264         opts->mss = mss;
 265         opts->options |= XT_SYNPROXY_OPT_MSS;
 266
 267         if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
 268                 synproxy_check_timestamp_cookie(opts);
 269
 270         synproxy_send_server_syn(snet, skb, th, opts, recv_seq);
 271         return true;
 272 }
 273
 274 static unsigned int
 275 synproxy_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 276 {
 277         const struct xt_synproxy_info *info = par->targinfo;
 278         struct synproxy_net *snet = synproxy_pernet(par->net);
 279         struct synproxy_options opts = {};
 280         struct tcphdr *th, _th;
 281
 282         if (nf_ip6_checksum(skb, par->hooknum, par->thoff, IPPROTO_TCP))
 283                 return NF_DROP;
 284
 285         th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
 286         if (th == NULL)
 287                 return NF_DROP;
 288
 289         if (!synproxy_parse_options(skb, par->thoff, th, &opts))
 290                 return NF_DROP;
 291
 292         if (th->syn && !(th->ack || th->fin || th->rst)) {
 293                 /* Initial SYN from client */
 294                 this_cpu_inc(snet->stats->syn_received);
 295
 296                 if (th->ece && th->cwr)
 297                         opts.options |= XT_SYNPROXY_OPT_ECN;
 298
 299                 opts.options &= info->options;
 300                 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
 301                         synproxy_init_timestamp_cookie(info, &opts);
 302                 else
 303                         opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
 304                                           XT_SYNPROXY_OPT_SACK_PERM |
 305                                           XT_SYNPROXY_OPT_ECN);
 306
 307                 synproxy_send_client_synack(snet, skb, th, &opts);
 308                 return NF_DROP;
 309
 310         } else if (th->ack && !(th->fin || th->rst || th->syn)) {
 311                 /* ACK from client */
 312                 synproxy_recv_client_ack(snet, skb, th, &opts, ntohl(th->seq));
 313                 return NF_DROP;
 314         }
 315
 316         return XT_CONTINUE;
 317 }
 318
 319 static unsigned int ipv6_synproxy_hook(void *priv,
 320                                        struct sk_buff *skb,
 321                                        const struct nf_hook_state *nhs)
 322 {
 323         struct synproxy_net *snet = synproxy_pernet(nhs->net);
 324         enum ip_conntrack_info ctinfo;
 325         struct nf_conn *ct;
 326         struct nf_conn_synproxy *synproxy;
 327         struct synproxy_options opts = {};
 328         const struct ip_ct_tcp *state;
 329         struct tcphdr *th, _th;
 330         __be16 frag_off;
 331         u8 nexthdr;
 332         int thoff;
 333
 334         ct = nf_ct_get(skb, &ctinfo);
 335         if (ct == NULL)
 336                 return NF_ACCEPT;
 337
 338         synproxy = nfct_synproxy(ct);
 339         if (synproxy == NULL)
 340                 return NF_ACCEPT;
 341
 342         if (nf_is_loopback_packet(skb))
 343                 return NF_ACCEPT;
 344
 345         nexthdr = ipv6_hdr(skb)->nexthdr;
 346         thoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
 347                                  &frag_off);
 348         if (thoff < 0)
 349                 return NF_ACCEPT;
 350
 351         th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
 352         if (th == NULL)
 353                 return NF_DROP;
 354
 355         state = &ct->proto.tcp;
 356         switch (state->state) {
 357         case TCP_CONNTRACK_CLOSE:
 358                 if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
 359                         nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
 360                                                       ntohl(th->seq) + 1);
 361                         break;
 362                 }
 363
 364                 if (!th->syn || th->ack ||
 365                     CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
 366                         break;
 367
 368                 /* Reopened connection - reset the sequence number and timestamp
 369                  * adjustments, they will get initialized once the connection is
 370                  * reestablished.
 371                  */
 372                 nf_ct_seqadj_init(ct, ctinfo, 0);
 373                 synproxy->tsoff = 0;
 374                 this_cpu_inc(snet->stats->conn_reopened);
 375
 376                 /* fall through */
 377         case TCP_CONNTRACK_SYN_SENT:
 378                 if (!synproxy_parse_options(skb, thoff, th, &opts))
 379                         return NF_DROP;
 380
 381                 if (!th->syn && th->ack &&
 382                     CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
 383                         /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
 384                          * therefore we need to add 1 to make the SYN sequence
 385                          * number match the one of first SYN.
 386                          */
 387                         if (synproxy_recv_client_ack(snet, skb, th, &opts,
 388                                                      ntohl(th->seq) + 1))
 389                                 this_cpu_inc(snet->stats->cookie_retrans);
 390
 391                         return NF_DROP;
 392                 }
 393
 394                 synproxy->isn = ntohl(th->ack_seq);
 395                 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
 396                         synproxy->its = opts.tsecr;
 397                 break;
 398         case TCP_CONNTRACK_SYN_RECV:
 399                 if (!th->syn || !th->ack)
 400                         break;
 401
 402                 if (!synproxy_parse_options(skb, thoff, th, &opts))
 403                         return NF_DROP;
 404
 405                 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
 406                         synproxy->tsoff = opts.tsval - synproxy->its;
 407
 408                 opts.options &= ~(XT_SYNPROXY_OPT_MSS |
 409                                   XT_SYNPROXY_OPT_WSCALE |
 410                                   XT_SYNPROXY_OPT_SACK_PERM);
 411
 412                 swap(opts.tsval, opts.tsecr);
 413                 synproxy_send_server_ack(snet, state, skb, th, &opts);
 414
 415                 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
 416
 417                 swap(opts.tsval, opts.tsecr);
 418                 synproxy_send_client_ack(snet, skb, th, &opts);
 419
 420                 consume_skb(skb);
 421                 return NF_STOLEN;
 422         default:
 423                 break;
 424         }
 425
 426         synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
 427         return NF_ACCEPT;
 428 }
 429
 430 static int synproxy_tg6_check(const struct xt_tgchk_param *par)
 431 {
 432         const struct ip6t_entry *e = par->entryinfo;
 433
 434         if (!(e->ipv6.flags & IP6T_F_PROTO) ||
 435             e->ipv6.proto != IPPROTO_TCP ||
 436             e->ipv6.invflags & XT_INV_PROTO)
 437                 return -EINVAL;
 438
 439         return nf_ct_l3proto_try_module_get(par->family);
 440 }
 441
 442 static void synproxy_tg6_destroy(const struct xt_tgdtor_param *par)
 443 {
 444         nf_ct_l3proto_module_put(par->family);
 445 }
 446
 447 static struct xt_target synproxy_tg6_reg __read_mostly = {
 448         .name           = "SYNPROXY",
 449         .family         = NFPROTO_IPV6,
 450         .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
 451         .target         = synproxy_tg6,
 452         .targetsize     = sizeof(struct xt_synproxy_info),
 453         .checkentry     = synproxy_tg6_check,
 454         .destroy        = synproxy_tg6_destroy,
 455         .me             = THIS_MODULE,
 456 };
 457
 458 static struct nf_hook_ops ipv6_synproxy_ops[] __read_mostly = {
 459         {
 460                 .hook           = ipv6_synproxy_hook,
 461                 .pf             = NFPROTO_IPV6,
 462                 .hooknum        = NF_INET_LOCAL_IN,
 463                 .priority       = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
 464         },
 465         {
 466                 .hook           = ipv6_synproxy_hook,
 467                 .pf             = NFPROTO_IPV6,
 468                 .hooknum        = NF_INET_POST_ROUTING,
 469                 .priority       = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
 470         },
 471 };
 472
 473 static int __init synproxy_tg6_init(void)
 474 {
 475         int err;
 476
 477         err = nf_register_hooks(ipv6_synproxy_ops,
 478                                 ARRAY_SIZE(ipv6_synproxy_ops));
 479         if (err < 0)
 480                 goto err1;
 481
 482         err = xt_register_target(&synproxy_tg6_reg);
 483         if (err < 0)
 484                 goto err2;
 485
 486         return 0;
 487
 488 err2:
 489         nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops));
 490 err1:
 491         return err;
 492 }
 493
 494 static void __exit synproxy_tg6_exit(void)
 495 {
 496         xt_unregister_target(&synproxy_tg6_reg);
 497         nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops));
 498 }
 499
 500 module_init(synproxy_tg6_init);
 501 module_exit(synproxy_tg6_exit);
 502
 503 MODULE_LICENSE("GPL");
 504 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");