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>"); 527