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/tcp.h> 12 13 #include <linux/netfilter_ipv4/ip_tables.h> 14 #include <linux/netfilter/x_tables.h> 15 #include <linux/netfilter/xt_SYNPROXY.h> 16 #include <net/netfilter/nf_conntrack.h> 17 #include <net/netfilter/nf_conntrack_seqadj.h> 18 #include <net/netfilter/nf_conntrack_synproxy.h> 19 20 static struct iphdr * 21 synproxy_build_ip(struct net *net, struct sk_buff *skb, __be32 saddr, 22 __be32 daddr) 23 { 24 struct iphdr *iph; 25 26 skb_reset_network_header(skb); 27 iph = skb_put(skb, sizeof(*iph)); 28 iph->version = 4; 29 iph->ihl = sizeof(*iph) / 4; 30 iph->tos = 0; 31 iph->id = 0; 32 iph->frag_off = htons(IP_DF); 33 iph->ttl = net->ipv4.sysctl_ip_default_ttl; 34 iph->protocol = IPPROTO_TCP; 35 iph->check = 0; 36 iph->saddr = saddr; 37 iph->daddr = daddr; 38 39 return iph; 40 } 41 42 static void 43 synproxy_send_tcp(struct net *net, 44 const struct sk_buff *skb, struct sk_buff *nskb, 45 struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo, 46 struct iphdr *niph, struct tcphdr *nth, 47 unsigned int tcp_hdr_size) 48 { 49 nth->check = ~tcp_v4_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 skb_dst_set_noref(nskb, skb_dst(skb)); 55 nskb->protocol = htons(ETH_P_IP); 56 if (ip_route_me_harder(net, nskb, RTN_UNSPEC)) 57 goto free_nskb; 58 59 if (nfct) { 60 nf_ct_set(nskb, (struct nf_conn *)nfct, ctinfo); 61 nf_conntrack_get(nfct); 62 } 63 64 ip_local_out(net, nskb->sk, nskb); 65 return; 66 67 free_nskb: 68 kfree_skb(nskb); 69 } 70 71 static void 72 synproxy_send_client_synack(struct net *net, 73 const struct sk_buff *skb, const struct tcphdr *th, 74 const struct synproxy_options *opts) 75 { 76 struct sk_buff *nskb; 77 struct iphdr *iph, *niph; 78 struct tcphdr *nth; 79 unsigned int tcp_hdr_size; 80 u16 mss = opts->mss; 81 82 iph = ip_hdr(skb); 83 84 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); 85 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, 86 GFP_ATOMIC); 87 if (nskb == NULL) 88 return; 89 skb_reserve(nskb, MAX_TCP_HEADER); 90 91 niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr); 92 93 skb_reset_transport_header(nskb); 94 nth = skb_put(nskb, tcp_hdr_size); 95 nth->source = th->dest; 96 nth->dest = th->source; 97 nth->seq = htonl(__cookie_v4_init_sequence(iph, th, &mss)); 98 nth->ack_seq = htonl(ntohl(th->seq) + 1); 99 tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK; 100 if (opts->options & XT_SYNPROXY_OPT_ECN) 101 tcp_flag_word(nth) |= TCP_FLAG_ECE; 102 nth->doff = tcp_hdr_size / 4; 103 nth->window = 0; 104 nth->check = 0; 105 nth->urg_ptr = 0; 106 107 synproxy_build_options(nth, opts); 108 109 synproxy_send_tcp(net, skb, nskb, skb_nfct(skb), 110 IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size); 111 } 112 113 static void 114 synproxy_send_server_syn(struct net *net, 115 const struct sk_buff *skb, const struct tcphdr *th, 116 const struct synproxy_options *opts, u32 recv_seq) 117 { 118 struct synproxy_net *snet = synproxy_pernet(net); 119 struct sk_buff *nskb; 120 struct iphdr *iph, *niph; 121 struct tcphdr *nth; 122 unsigned int tcp_hdr_size; 123 124 iph = ip_hdr(skb); 125 126 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); 127 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, 128 GFP_ATOMIC); 129 if (nskb == NULL) 130 return; 131 skb_reserve(nskb, MAX_TCP_HEADER); 132 133 niph = synproxy_build_ip(net, nskb, iph->saddr, iph->daddr); 134 135 skb_reset_transport_header(nskb); 136 nth = skb_put(nskb, tcp_hdr_size); 137 nth->source = th->source; 138 nth->dest = th->dest; 139 nth->seq = htonl(recv_seq - 1); 140 /* ack_seq is used to relay our ISN to the synproxy hook to initialize 141 * sequence number translation once a connection tracking entry exists. 142 */ 143 nth->ack_seq = htonl(ntohl(th->ack_seq) - 1); 144 tcp_flag_word(nth) = TCP_FLAG_SYN; 145 if (opts->options & XT_SYNPROXY_OPT_ECN) 146 tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR; 147 nth->doff = tcp_hdr_size / 4; 148 nth->window = th->window; 149 nth->check = 0; 150 nth->urg_ptr = 0; 151 152 synproxy_build_options(nth, opts); 153 154 synproxy_send_tcp(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW, 155 niph, nth, tcp_hdr_size); 156 } 157 158 static void 159 synproxy_send_server_ack(struct net *net, 160 const struct ip_ct_tcp *state, 161 const struct sk_buff *skb, const struct tcphdr *th, 162 const struct synproxy_options *opts) 163 { 164 struct sk_buff *nskb; 165 struct iphdr *iph, *niph; 166 struct tcphdr *nth; 167 unsigned int tcp_hdr_size; 168 169 iph = ip_hdr(skb); 170 171 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); 172 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, 173 GFP_ATOMIC); 174 if (nskb == NULL) 175 return; 176 skb_reserve(nskb, MAX_TCP_HEADER); 177 178 niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr); 179 180 skb_reset_transport_header(nskb); 181 nth = skb_put(nskb, tcp_hdr_size); 182 nth->source = th->dest; 183 nth->dest = th->source; 184 nth->seq = htonl(ntohl(th->ack_seq)); 185 nth->ack_seq = htonl(ntohl(th->seq) + 1); 186 tcp_flag_word(nth) = TCP_FLAG_ACK; 187 nth->doff = tcp_hdr_size / 4; 188 nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin); 189 nth->check = 0; 190 nth->urg_ptr = 0; 191 192 synproxy_build_options(nth, opts); 193 194 synproxy_send_tcp(net, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size); 195 } 196 197 static void 198 synproxy_send_client_ack(struct net *net, 199 const struct sk_buff *skb, const struct tcphdr *th, 200 const struct synproxy_options *opts) 201 { 202 struct sk_buff *nskb; 203 struct iphdr *iph, *niph; 204 struct tcphdr *nth; 205 unsigned int tcp_hdr_size; 206 207 iph = ip_hdr(skb); 208 209 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); 210 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, 211 GFP_ATOMIC); 212 if (nskb == NULL) 213 return; 214 skb_reserve(nskb, MAX_TCP_HEADER); 215 216 niph = synproxy_build_ip(net, nskb, iph->saddr, iph->daddr); 217 218 skb_reset_transport_header(nskb); 219 nth = skb_put(nskb, tcp_hdr_size); 220 nth->source = th->source; 221 nth->dest = th->dest; 222 nth->seq = htonl(ntohl(th->seq) + 1); 223 nth->ack_seq = th->ack_seq; 224 tcp_flag_word(nth) = TCP_FLAG_ACK; 225 nth->doff = tcp_hdr_size / 4; 226 nth->window = htons(ntohs(th->window) >> opts->wscale); 227 nth->check = 0; 228 nth->urg_ptr = 0; 229 230 synproxy_build_options(nth, opts); 231 232 synproxy_send_tcp(net, skb, nskb, skb_nfct(skb), 233 IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size); 234 } 235 236 static bool 237 synproxy_recv_client_ack(struct net *net, 238 const struct sk_buff *skb, const struct tcphdr *th, 239 struct synproxy_options *opts, u32 recv_seq) 240 { 241 struct synproxy_net *snet = synproxy_pernet(net); 242 int mss; 243 244 mss = __cookie_v4_check(ip_hdr(skb), th, ntohl(th->ack_seq) - 1); 245 if (mss == 0) { 246 this_cpu_inc(snet->stats->cookie_invalid); 247 return false; 248 } 249 250 this_cpu_inc(snet->stats->cookie_valid); 251 opts->mss = mss; 252 opts->options |= XT_SYNPROXY_OPT_MSS; 253 254 if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP) 255 synproxy_check_timestamp_cookie(opts); 256 257 synproxy_send_server_syn(net, skb, th, opts, recv_seq); 258 return true; 259 } 260 261 static unsigned int 262 synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par) 263 { 264 const struct xt_synproxy_info *info = par->targinfo; 265 struct net *net = xt_net(par); 266 struct synproxy_net *snet = synproxy_pernet(net); 267 struct synproxy_options opts = {}; 268 struct tcphdr *th, _th; 269 270 if (nf_ip_checksum(skb, xt_hooknum(par), par->thoff, IPPROTO_TCP)) 271 return NF_DROP; 272 273 th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th); 274 if (th == NULL) 275 return NF_DROP; 276 277 if (!synproxy_parse_options(skb, par->thoff, th, &opts)) 278 return NF_DROP; 279 280 if (th->syn && !(th->ack || th->fin || th->rst)) { 281 /* Initial SYN from client */ 282 this_cpu_inc(snet->stats->syn_received); 283 284 if (th->ece && th->cwr) 285 opts.options |= XT_SYNPROXY_OPT_ECN; 286 287 opts.options &= info->options; 288 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) 289 synproxy_init_timestamp_cookie(info, &opts); 290 else 291 opts.options &= ~(XT_SYNPROXY_OPT_WSCALE | 292 XT_SYNPROXY_OPT_SACK_PERM | 293 XT_SYNPROXY_OPT_ECN); 294 295 synproxy_send_client_synack(net, skb, th, &opts); 296 consume_skb(skb); 297 return NF_STOLEN; 298 } else if (th->ack && !(th->fin || th->rst || th->syn)) { 299 /* ACK from client */ 300 if (synproxy_recv_client_ack(net, skb, th, &opts, ntohl(th->seq))) { 301 consume_skb(skb); 302 return NF_STOLEN; 303 } else { 304 return NF_DROP; 305 } 306 } 307 308 return XT_CONTINUE; 309 } 310 311 static unsigned int ipv4_synproxy_hook(void *priv, 312 struct sk_buff *skb, 313 const struct nf_hook_state *nhs) 314 { 315 struct net *net = nhs->net; 316 struct synproxy_net *snet = synproxy_pernet(net); 317 enum ip_conntrack_info ctinfo; 318 struct nf_conn *ct; 319 struct nf_conn_synproxy *synproxy; 320 struct synproxy_options opts = {}; 321 const struct ip_ct_tcp *state; 322 struct tcphdr *th, _th; 323 unsigned int thoff; 324 325 ct = nf_ct_get(skb, &ctinfo); 326 if (ct == NULL) 327 return NF_ACCEPT; 328 329 synproxy = nfct_synproxy(ct); 330 if (synproxy == NULL) 331 return NF_ACCEPT; 332 333 if (nf_is_loopback_packet(skb) || 334 ip_hdr(skb)->protocol != IPPROTO_TCP) 335 return NF_ACCEPT; 336 337 thoff = ip_hdrlen(skb); 338 th = skb_header_pointer(skb, thoff, sizeof(_th), &_th); 339 if (th == NULL) 340 return NF_DROP; 341 342 state = &ct->proto.tcp; 343 switch (state->state) { 344 case TCP_CONNTRACK_CLOSE: 345 if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) { 346 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - 347 ntohl(th->seq) + 1); 348 break; 349 } 350 351 if (!th->syn || th->ack || 352 CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) 353 break; 354 355 /* Reopened connection - reset the sequence number and timestamp 356 * adjustments, they will get initialized once the connection is 357 * reestablished. 358 */ 359 nf_ct_seqadj_init(ct, ctinfo, 0); 360 synproxy->tsoff = 0; 361 this_cpu_inc(snet->stats->conn_reopened); 362 363 /* fall through */ 364 case TCP_CONNTRACK_SYN_SENT: 365 if (!synproxy_parse_options(skb, thoff, th, &opts)) 366 return NF_DROP; 367 368 if (!th->syn && th->ack && 369 CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) { 370 /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1, 371 * therefore we need to add 1 to make the SYN sequence 372 * number match the one of first SYN. 373 */ 374 if (synproxy_recv_client_ack(net, skb, th, &opts, 375 ntohl(th->seq) + 1)) { 376 this_cpu_inc(snet->stats->cookie_retrans); 377 consume_skb(skb); 378 return NF_STOLEN; 379 } else { 380 return NF_DROP; 381 } 382 } 383 384 synproxy->isn = ntohl(th->ack_seq); 385 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) 386 synproxy->its = opts.tsecr; 387 break; 388 case TCP_CONNTRACK_SYN_RECV: 389 if (!th->syn || !th->ack) 390 break; 391 392 if (!synproxy_parse_options(skb, thoff, th, &opts)) 393 return NF_DROP; 394 395 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) 396 synproxy->tsoff = opts.tsval - synproxy->its; 397 398 opts.options &= ~(XT_SYNPROXY_OPT_MSS | 399 XT_SYNPROXY_OPT_WSCALE | 400 XT_SYNPROXY_OPT_SACK_PERM); 401 402 swap(opts.tsval, opts.tsecr); 403 synproxy_send_server_ack(net, state, skb, th, &opts); 404 405 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq)); 406 407 swap(opts.tsval, opts.tsecr); 408 synproxy_send_client_ack(net, skb, th, &opts); 409 410 consume_skb(skb); 411 return NF_STOLEN; 412 default: 413 break; 414 } 415 416 synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy); 417 return NF_ACCEPT; 418 } 419 420 static const struct nf_hook_ops ipv4_synproxy_ops[] = { 421 { 422 .hook = ipv4_synproxy_hook, 423 .pf = NFPROTO_IPV4, 424 .hooknum = NF_INET_LOCAL_IN, 425 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1, 426 }, 427 { 428 .hook = ipv4_synproxy_hook, 429 .pf = NFPROTO_IPV4, 430 .hooknum = NF_INET_POST_ROUTING, 431 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1, 432 }, 433 }; 434 435 static int synproxy_tg4_check(const struct xt_tgchk_param *par) 436 { 437 struct synproxy_net *snet = synproxy_pernet(par->net); 438 const struct ipt_entry *e = par->entryinfo; 439 int err; 440 441 if (e->ip.proto != IPPROTO_TCP || 442 e->ip.invflags & XT_INV_PROTO) 443 return -EINVAL; 444 445 err = nf_ct_netns_get(par->net, par->family); 446 if (err) 447 return err; 448 449 if (snet->hook_ref4 == 0) { 450 err = nf_register_net_hooks(par->net, ipv4_synproxy_ops, 451 ARRAY_SIZE(ipv4_synproxy_ops)); 452 if (err) { 453 nf_ct_netns_put(par->net, par->family); 454 return err; 455 } 456 } 457 458 snet->hook_ref4++; 459 return err; 460 } 461 462 static void synproxy_tg4_destroy(const struct xt_tgdtor_param *par) 463 { 464 struct synproxy_net *snet = synproxy_pernet(par->net); 465 466 snet->hook_ref4--; 467 if (snet->hook_ref4 == 0) 468 nf_unregister_net_hooks(par->net, ipv4_synproxy_ops, 469 ARRAY_SIZE(ipv4_synproxy_ops)); 470 nf_ct_netns_put(par->net, par->family); 471 } 472 473 static struct xt_target synproxy_tg4_reg __read_mostly = { 474 .name = "SYNPROXY", 475 .family = NFPROTO_IPV4, 476 .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD), 477 .target = synproxy_tg4, 478 .targetsize = sizeof(struct xt_synproxy_info), 479 .checkentry = synproxy_tg4_check, 480 .destroy = synproxy_tg4_destroy, 481 .me = THIS_MODULE, 482 }; 483 484 static int __init synproxy_tg4_init(void) 485 { 486 return xt_register_target(&synproxy_tg4_reg); 487 } 488 489 static void __exit synproxy_tg4_exit(void) 490 { 491 xt_unregister_target(&synproxy_tg4_reg); 492 } 493 494 module_init(synproxy_tg4_init); 495 module_exit(synproxy_tg4_exit); 496 497 MODULE_LICENSE("GPL"); 498 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>"); 499