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>"); 505