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 sk_buff *skb, struct sk_buff *nskb,
  41                   struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
  42                   struct ipv6hdr *niph, struct tcphdr *nth,
  43                   unsigned int tcp_hdr_size)
  44 {
  45         struct net *net = nf_ct_net((struct nf_conn *)nfct);
  46         struct dst_entry *dst;
  47         struct flowi6 fl6;
  48
  49         nth->check = ~tcp_v6_check(tcp_hdr_size, &niph->saddr, &niph->daddr, 0);
  50         nskb->ip_summed   = CHECKSUM_PARTIAL;
  51         nskb->csum_start  = (unsigned char *)nth - nskb->head;
  52         nskb->csum_offset = offsetof(struct tcphdr, check);
  53
  54         memset(&fl6, 0, sizeof(fl6));
  55         fl6.flowi6_proto = IPPROTO_TCP;
  56         fl6.saddr = niph->saddr;
  57         fl6.daddr = niph->daddr;
  58         fl6.fl6_sport = nth->source;
  59         fl6.fl6_dport = nth->dest;
  60         security_skb_classify_flow((struct sk_buff *)skb, flowi6_to_flowi(&fl6));
  61         dst = ip6_route_output(net, NULL, &fl6);
  62         if (dst == NULL || dst->error) {
  63                 dst_release(dst);
  64                 goto free_nskb;
  65         }
  66         dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
  67         if (IS_ERR(dst))
  68                 goto free_nskb;
  69
  70         skb_dst_set(nskb, dst);
  71
  72         if (nfct) {
  73                 nskb->nfct = nfct;
  74                 nskb->nfctinfo = ctinfo;
  75                 nf_conntrack_get(nfct);
  76         }
  77
  78         ip6_local_out(nskb);
  79         return;
  80
  81 free_nskb:
  82         kfree_skb(nskb);
  83 }
  84
  85 static void
  86 synproxy_send_client_synack(const struct sk_buff *skb, const struct tcphdr *th,
  87                             const struct synproxy_options *opts)
  88 {
  89         struct sk_buff *nskb;
  90         struct ipv6hdr *iph, *niph;
  91         struct tcphdr *nth;
  92         unsigned int tcp_hdr_size;
  93         u16 mss = opts->mss;
  94
  95         iph = ipv6_hdr(skb);
  96
  97         tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
  98         nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
  99                          GFP_ATOMIC);
 100         if (nskb == NULL)
 101                 return;
 102         skb_reserve(nskb, MAX_TCP_HEADER);
 103
 104         niph = synproxy_build_ip(nskb, &iph->daddr, &iph->saddr);
 105
 106         skb_reset_transport_header(nskb);
 107         nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
 108         nth->source     = th->dest;
 109         nth->dest       = th->source;
 110         nth->seq        = htonl(__cookie_v6_init_sequence(iph, th, &mss));
 111         nth->ack_seq    = htonl(ntohl(th->seq) + 1);
 112         tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
 113         if (opts->options & XT_SYNPROXY_OPT_ECN)
 114                 tcp_flag_word(nth) |= TCP_FLAG_ECE;
 115         nth->doff       = tcp_hdr_size / 4;
 116         nth->window     = 0;
 117         nth->check      = 0;
 118         nth->urg_ptr    = 0;
 119
 120         synproxy_build_options(nth, opts);
 121
 122         synproxy_send_tcp(skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
 123                           niph, nth, tcp_hdr_size);
 124 }
 125
 126 static void
 127 synproxy_send_server_syn(const struct synproxy_net *snet,
 128                          const struct sk_buff *skb, const struct tcphdr *th,
 129                          const struct synproxy_options *opts, u32 recv_seq)
 130 {
 131         struct sk_buff *nskb;
 132         struct ipv6hdr *iph, *niph;
 133         struct tcphdr *nth;
 134         unsigned int tcp_hdr_size;
 135
 136         iph = ipv6_hdr(skb);
 137
 138         tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
 139         nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
 140                          GFP_ATOMIC);
 141         if (nskb == NULL)
 142                 return;
 143         skb_reserve(nskb, MAX_TCP_HEADER);
 144
 145         niph = synproxy_build_ip(nskb, &iph->saddr, &iph->daddr);
 146
 147         skb_reset_transport_header(nskb);
 148         nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
 149         nth->source     = th->source;
 150         nth->dest       = th->dest;
 151         nth->seq        = htonl(recv_seq - 1);
 152         /* ack_seq is used to relay our ISN to the synproxy hook to initialize
 153          * sequence number translation once a connection tracking entry exists.
 154          */
 155         nth->ack_seq    = htonl(ntohl(th->ack_seq) - 1);
 156         tcp_flag_word(nth) = TCP_FLAG_SYN;
 157         if (opts->options & XT_SYNPROXY_OPT_ECN)
 158                 tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
 159         nth->doff       = tcp_hdr_size / 4;
 160         nth->window     = th->window;
 161         nth->check      = 0;
 162         nth->urg_ptr    = 0;
 163
 164         synproxy_build_options(nth, opts);
 165
 166         synproxy_send_tcp(skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
 167                           niph, nth, tcp_hdr_size);
 168 }
 169
 170 static void
 171 synproxy_send_server_ack(const struct synproxy_net *snet,
 172                          const struct ip_ct_tcp *state,
 173                          const struct sk_buff *skb, const struct tcphdr *th,
 174                          const struct synproxy_options *opts)
 175 {
 176         struct sk_buff *nskb;
 177         struct ipv6hdr *iph, *niph;
 178         struct tcphdr *nth;
 179         unsigned int tcp_hdr_size;
 180
 181         iph = ipv6_hdr(skb);
 182
 183         tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
 184         nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
 185                          GFP_ATOMIC);
 186         if (nskb == NULL)
 187                 return;
 188         skb_reserve(nskb, MAX_TCP_HEADER);
 189
 190         niph = synproxy_build_ip(nskb, &iph->daddr, &iph->saddr);
 191
 192         skb_reset_transport_header(nskb);
 193         nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
 194         nth->source     = th->dest;
 195         nth->dest       = th->source;
 196         nth->seq        = htonl(ntohl(th->ack_seq));
 197         nth->ack_seq    = htonl(ntohl(th->seq) + 1);
 198         tcp_flag_word(nth) = TCP_FLAG_ACK;
 199         nth->doff       = tcp_hdr_size / 4;
 200         nth->window     = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
 201         nth->check      = 0;
 202         nth->urg_ptr    = 0;
 203
 204         synproxy_build_options(nth, opts);
 205
 206         synproxy_send_tcp(skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
 207 }
 208
 209 static void
 210 synproxy_send_client_ack(const struct synproxy_net *snet,
 211                          const struct sk_buff *skb, const struct tcphdr *th,
 212                          const struct synproxy_options *opts)
 213 {
 214         struct sk_buff *nskb;
 215         struct ipv6hdr *iph, *niph;
 216         struct tcphdr *nth;
 217         unsigned int tcp_hdr_size;
 218
 219         iph = ipv6_hdr(skb);
 220
 221         tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
 222         nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
 223                          GFP_ATOMIC);
 224         if (nskb == NULL)
 225                 return;
 226         skb_reserve(nskb, MAX_TCP_HEADER);
 227
 228         niph = synproxy_build_ip(nskb, &iph->saddr, &iph->daddr);
 229
 230         skb_reset_transport_header(nskb);
 231         nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
 232         nth->source     = th->source;
 233         nth->dest       = th->dest;
 234         nth->seq        = htonl(ntohl(th->seq) + 1);
 235         nth->ack_seq    = th->ack_seq;
 236         tcp_flag_word(nth) = TCP_FLAG_ACK;
 237         nth->doff       = tcp_hdr_size / 4;
 238         nth->window     = ntohs(htons(th->window) >> opts->wscale);
 239         nth->check      = 0;
 240         nth->urg_ptr    = 0;
 241
 242         synproxy_build_options(nth, opts);
 243
 244         synproxy_send_tcp(skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
 245 }
 246
 247 static bool
 248 synproxy_recv_client_ack(const struct synproxy_net *snet,
 249                          const struct sk_buff *skb, const struct tcphdr *th,
 250                          struct synproxy_options *opts, u32 recv_seq)
 251 {
 252         int mss;
 253
 254         mss = __cookie_v6_check(ipv6_hdr(skb), th, ntohl(th->ack_seq) - 1);
 255         if (mss == 0) {
 256                 this_cpu_inc(snet->stats->cookie_invalid);
 257                 return false;
 258         }
 259
 260         this_cpu_inc(snet->stats->cookie_valid);
 261         opts->mss = mss;
 262
 263         if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
 264                 synproxy_check_timestamp_cookie(opts);
 265
 266         synproxy_send_server_syn(snet, skb, th, opts, recv_seq);
 267         return true;
 268 }
 269
 270 static unsigned int
 271 synproxy_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 272 {
 273         const struct xt_synproxy_info *info = par->targinfo;
 274         struct synproxy_net *snet = synproxy_pernet(dev_net(par->in));
 275         struct synproxy_options opts = {};
 276         struct tcphdr *th, _th;
 277
 278         if (nf_ip6_checksum(skb, par->hooknum, par->thoff, IPPROTO_TCP))
 279                 return NF_DROP;
 280
 281         th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
 282         if (th == NULL)
 283                 return NF_DROP;
 284
 285         if (!synproxy_parse_options(skb, par->thoff, th, &opts))
 286                 return NF_DROP;
 287
 288         if (th->syn && !(th->ack || th->fin || th->rst)) {
 289                 /* Initial SYN from client */
 290                 this_cpu_inc(snet->stats->syn_received);
 291
 292                 if (th->ece && th->cwr)
 293                         opts.options |= XT_SYNPROXY_OPT_ECN;
 294
 295                 opts.options &= info->options;
 296                 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
 297                         synproxy_init_timestamp_cookie(info, &opts);
 298                 else
 299                         opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
 300                                           XT_SYNPROXY_OPT_SACK_PERM |
 301                                           XT_SYNPROXY_OPT_ECN);
 302
 303                 synproxy_send_client_synack(skb, th, &opts);
 304                 return NF_DROP;
 305
 306         } else if (th->ack && !(th->fin || th->rst || th->syn)) {
 307                 /* ACK from client */
 308                 synproxy_recv_client_ack(snet, skb, th, &opts, ntohl(th->seq));
 309                 return NF_DROP;
 310         }
 311
 312         return XT_CONTINUE;
 313 }
 314
 315 static unsigned int ipv6_synproxy_hook(const struct nf_hook_ops *ops,
 316                                        struct sk_buff *skb,
 317                                        const struct net_device *in,
 318                                        const struct net_device *out,
 319                                        int (*okfn)(struct sk_buff *))
 320 {
 321         struct synproxy_net *snet = synproxy_pernet(dev_net(in ? : out));
 322         enum ip_conntrack_info ctinfo;
 323         struct nf_conn *ct;
 324         struct nf_conn_synproxy *synproxy;
 325         struct synproxy_options opts = {};
 326         const struct ip_ct_tcp *state;
 327         struct tcphdr *th, _th;
 328         __be16 frag_off;
 329         u8 nexthdr;
 330         int thoff;
 331
 332         ct = nf_ct_get(skb, &ctinfo);
 333         if (ct == NULL)
 334                 return NF_ACCEPT;
 335
 336         synproxy = nfct_synproxy(ct);
 337         if (synproxy == NULL)
 338                 return NF_ACCEPT;
 339
 340         if (nf_is_loopback_packet(skb))
 341                 return NF_ACCEPT;
 342
 343         nexthdr = ipv6_hdr(skb)->nexthdr;
 344         thoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
 345                                  &frag_off);
 346         if (thoff < 0)
 347                 return NF_ACCEPT;
 348
 349         th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
 350         if (th == NULL)
 351                 return NF_DROP;
 352
 353         state = &ct->proto.tcp;
 354         switch (state->state) {
 355         case TCP_CONNTRACK_CLOSE:
 356                 if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
 357                         nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
 358                                                       ntohl(th->seq) + 1);
 359                         break;
 360                 }
 361
 362                 if (!th->syn || th->ack ||
 363                     CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
 364                         break;
 365
 366                 /* Reopened connection - reset the sequence number and timestamp
 367                  * adjustments, they will get initialized once the connection is
 368                  * reestablished.
 369                  */
 370                 nf_ct_seqadj_init(ct, ctinfo, 0);
 371                 synproxy->tsoff = 0;
 372                 this_cpu_inc(snet->stats->conn_reopened);
 373
 374                 /* fall through */
 375         case TCP_CONNTRACK_SYN_SENT:
 376                 if (!synproxy_parse_options(skb, thoff, th, &opts))
 377                         return NF_DROP;
 378
 379                 if (!th->syn && th->ack &&
 380                     CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
 381                         /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
 382                          * therefore we need to add 1 to make the SYN sequence
 383                          * number match the one of first SYN.
 384                          */
 385                         if (synproxy_recv_client_ack(snet, skb, th, &opts,
 386                                                      ntohl(th->seq) + 1))
 387                                 this_cpu_inc(snet->stats->cookie_retrans);
 388
 389                         return NF_DROP;
 390                 }
 391
 392                 synproxy->isn = ntohl(th->ack_seq);
 393                 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
 394                         synproxy->its = opts.tsecr;
 395                 break;
 396         case TCP_CONNTRACK_SYN_RECV:
 397                 if (!th->syn || !th->ack)
 398                         break;
 399
 400                 if (!synproxy_parse_options(skb, thoff, th, &opts))
 401                         return NF_DROP;
 402
 403                 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
 404                         synproxy->tsoff = opts.tsval - synproxy->its;
 405
 406                 opts.options &= ~(XT_SYNPROXY_OPT_MSS |
 407                                   XT_SYNPROXY_OPT_WSCALE |
 408                                   XT_SYNPROXY_OPT_SACK_PERM);
 409
 410                 swap(opts.tsval, opts.tsecr);
 411                 synproxy_send_server_ack(snet, state, skb, th, &opts);
 412
 413                 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
 414
 415                 swap(opts.tsval, opts.tsecr);
 416                 synproxy_send_client_ack(snet, skb, th, &opts);
 417
 418                 consume_skb(skb);
 419                 return NF_STOLEN;
 420         default:
 421                 break;
 422         }
 423
 424         synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
 425         return NF_ACCEPT;
 426 }
 427
 428 static int synproxy_tg6_check(const struct xt_tgchk_param *par)
 429 {
 430         const struct ip6t_entry *e = par->entryinfo;
 431
 432         if (!(e->ipv6.flags & IP6T_F_PROTO) ||
 433             e->ipv6.proto != IPPROTO_TCP ||
 434             e->ipv6.invflags & XT_INV_PROTO)
 435                 return -EINVAL;
 436
 437         return nf_ct_l3proto_try_module_get(par->family);
 438 }
 439
 440 static void synproxy_tg6_destroy(const struct xt_tgdtor_param *par)
 441 {
 442         nf_ct_l3proto_module_put(par->family);
 443 }
 444
 445 static struct xt_target synproxy_tg6_reg __read_mostly = {
 446         .name           = "SYNPROXY",
 447         .family         = NFPROTO_IPV6,
 448         .target         = synproxy_tg6,
 449         .targetsize     = sizeof(struct xt_synproxy_info),
 450         .checkentry     = synproxy_tg6_check,
 451         .destroy        = synproxy_tg6_destroy,
 452         .me             = THIS_MODULE,
 453 };
 454
 455 static struct nf_hook_ops ipv6_synproxy_ops[] __read_mostly = {
 456         {
 457                 .hook           = ipv6_synproxy_hook,
 458                 .owner          = THIS_MODULE,
 459                 .pf             = NFPROTO_IPV6,
 460                 .hooknum        = NF_INET_LOCAL_IN,
 461                 .priority       = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
 462         },
 463         {
 464                 .hook           = ipv6_synproxy_hook,
 465                 .owner          = THIS_MODULE,
 466                 .pf             = NFPROTO_IPV6,
 467                 .hooknum        = NF_INET_POST_ROUTING,
 468                 .priority       = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
 469         },
 470 };
 471
 472 static int __init synproxy_tg6_init(void)
 473 {
 474         int err;
 475
 476         err = nf_register_hooks(ipv6_synproxy_ops,
 477                                 ARRAY_SIZE(ipv6_synproxy_ops));
 478         if (err < 0)
 479                 goto err1;
 480
 481         err = xt_register_target(&synproxy_tg6_reg);
 482         if (err < 0)
 483                 goto err2;
 484
 485         return 0;
 486
 487 err2:
 488         nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops));
 489 err1:
 490         return err;
 491 }
 492
 493 static void __exit synproxy_tg6_exit(void)
 494 {
 495         xt_unregister_target(&synproxy_tg6_reg);
 496         nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops));
 497 }
 498
 499 module_init(synproxy_tg6_init);
 500 module_exit(synproxy_tg6_exit);
 501
 502 MODULE_LICENSE("GPL");
 503 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");