1/* 2 * Transparent proxy support for Linux/iptables 3 * 4 * Copyright (c) 2006-2010 BalaBit IT Ltd. 5 * Author: Balazs Scheidler, Krisztian Kovacs 6 * 7 * This program is free software; you can redistribute it and/or modify 8 * it under the terms of the GNU General Public License version 2 as 9 * published by the Free Software Foundation. 10 * 11 */ 12#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 13#include <linux/module.h> 14#include <linux/skbuff.h> 15#include <linux/ip.h> 16#include <net/checksum.h> 17#include <net/udp.h> 18#include <net/tcp.h> 19#include <net/inet_sock.h> 20#include <net/inet_hashtables.h> 21#include <linux/inetdevice.h> 22#include <linux/netfilter/x_tables.h> 23#include <linux/netfilter_ipv4/ip_tables.h> 24 25#include <net/netfilter/ipv4/nf_defrag_ipv4.h> 26 27#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES) 28#define XT_TPROXY_HAVE_IPV6 1 29#include <net/if_inet6.h> 30#include <net/addrconf.h> 31#include <net/inet6_hashtables.h> 32#include <linux/netfilter_ipv6/ip6_tables.h> 33#include <net/netfilter/ipv6/nf_defrag_ipv6.h> 34#endif 35 36#include <linux/netfilter/xt_TPROXY.h> 37 38enum nf_tproxy_lookup_t { 39 NFT_LOOKUP_LISTENER, 40 NFT_LOOKUP_ESTABLISHED, 41}; 42 43static bool tproxy_sk_is_transparent(struct sock *sk) 44{ 45 switch (sk->sk_state) { 46 case TCP_TIME_WAIT: 47 if (inet_twsk(sk)->tw_transparent) 48 return true; 49 break; 50 case TCP_NEW_SYN_RECV: 51 if (inet_rsk(inet_reqsk(sk))->no_srccheck) 52 return true; 53 break; 54 default: 55 if (inet_sk(sk)->transparent) 56 return true; 57 } 58 59 sock_gen_put(sk); 60 return false; 61} 62 63static inline __be32 64tproxy_laddr4(struct sk_buff *skb, __be32 user_laddr, __be32 daddr) 65{ 66 struct in_device *indev; 67 __be32 laddr; 68 69 if (user_laddr) 70 return user_laddr; 71 72 laddr = 0; 73 rcu_read_lock(); 74 indev = __in_dev_get_rcu(skb->dev); 75 for_primary_ifa(indev) { 76 laddr = ifa->ifa_local; 77 break; 78 } endfor_ifa(indev); 79 rcu_read_unlock(); 80 81 return laddr ? laddr : daddr; 82} 83 84/* 85 * This is used when the user wants to intercept a connection matching 86 * an explicit iptables rule. In this case the sockets are assumed 87 * matching in preference order: 88 * 89 * - match: if there's a fully established connection matching the 90 * _packet_ tuple, it is returned, assuming the redirection 91 * already took place and we process a packet belonging to an 92 * established connection 93 * 94 * - match: if there's a listening socket matching the redirection 95 * (e.g. on-port & on-ip of the connection), it is returned, 96 * regardless if it was bound to 0.0.0.0 or an explicit 97 * address. The reasoning is that if there's an explicit rule, it 98 * does not really matter if the listener is bound to an interface 99 * or to 0. The user already stated that he wants redirection 100 * (since he added the rule). 101 * 102 * Please note that there's an overlap between what a TPROXY target 103 * and a socket match will match. Normally if you have both rules the 104 * "socket" match will be the first one, effectively all packets 105 * belonging to established connections going through that one. 106 */ 107static inline struct sock * 108nf_tproxy_get_sock_v4(struct net *net, const u8 protocol, 109 const __be32 saddr, const __be32 daddr, 110 const __be16 sport, const __be16 dport, 111 const struct net_device *in, 112 const enum nf_tproxy_lookup_t lookup_type) 113{ 114 struct sock *sk; 115 116 switch (protocol) { 117 case IPPROTO_TCP: 118 switch (lookup_type) { 119 case NFT_LOOKUP_LISTENER: 120 sk = inet_lookup_listener(net, &tcp_hashinfo, 121 saddr, sport, 122 daddr, dport, 123 in->ifindex); 124 125 /* NOTE: we return listeners even if bound to 126 * 0.0.0.0, those are filtered out in 127 * xt_socket, since xt_TPROXY needs 0 bound 128 * listeners too 129 */ 130 break; 131 case NFT_LOOKUP_ESTABLISHED: 132 sk = inet_lookup_established(net, &tcp_hashinfo, 133 saddr, sport, daddr, dport, 134 in->ifindex); 135 break; 136 default: 137 BUG(); 138 } 139 break; 140 case IPPROTO_UDP: 141 sk = udp4_lib_lookup(net, saddr, sport, daddr, dport, 142 in->ifindex); 143 if (sk) { 144 int connected = (sk->sk_state == TCP_ESTABLISHED); 145 int wildcard = (inet_sk(sk)->inet_rcv_saddr == 0); 146 147 /* NOTE: we return listeners even if bound to 148 * 0.0.0.0, those are filtered out in 149 * xt_socket, since xt_TPROXY needs 0 bound 150 * listeners too 151 */ 152 if ((lookup_type == NFT_LOOKUP_ESTABLISHED && (!connected || wildcard)) || 153 (lookup_type == NFT_LOOKUP_LISTENER && connected)) { 154 sock_put(sk); 155 sk = NULL; 156 } 157 } 158 break; 159 default: 160 WARN_ON(1); 161 sk = NULL; 162 } 163 164 pr_debug("tproxy socket lookup: proto %u %08x:%u -> %08x:%u, lookup type: %d, sock %p\n", 165 protocol, ntohl(saddr), ntohs(sport), ntohl(daddr), ntohs(dport), lookup_type, sk); 166 167 return sk; 168} 169 170#ifdef XT_TPROXY_HAVE_IPV6 171static inline struct sock * 172nf_tproxy_get_sock_v6(struct net *net, const u8 protocol, 173 const struct in6_addr *saddr, const struct in6_addr *daddr, 174 const __be16 sport, const __be16 dport, 175 const struct net_device *in, 176 const enum nf_tproxy_lookup_t lookup_type) 177{ 178 struct sock *sk; 179 180 switch (protocol) { 181 case IPPROTO_TCP: 182 switch (lookup_type) { 183 case NFT_LOOKUP_LISTENER: 184 sk = inet6_lookup_listener(net, &tcp_hashinfo, 185 saddr, sport, 186 daddr, ntohs(dport), 187 in->ifindex); 188 189 /* NOTE: we return listeners even if bound to 190 * 0.0.0.0, those are filtered out in 191 * xt_socket, since xt_TPROXY needs 0 bound 192 * listeners too 193 */ 194 break; 195 case NFT_LOOKUP_ESTABLISHED: 196 sk = __inet6_lookup_established(net, &tcp_hashinfo, 197 saddr, sport, daddr, ntohs(dport), 198 in->ifindex); 199 break; 200 default: 201 BUG(); 202 } 203 break; 204 case IPPROTO_UDP: 205 sk = udp6_lib_lookup(net, saddr, sport, daddr, dport, 206 in->ifindex); 207 if (sk) { 208 int connected = (sk->sk_state == TCP_ESTABLISHED); 209 int wildcard = ipv6_addr_any(&sk->sk_v6_rcv_saddr); 210 211 /* NOTE: we return listeners even if bound to 212 * 0.0.0.0, those are filtered out in 213 * xt_socket, since xt_TPROXY needs 0 bound 214 * listeners too 215 */ 216 if ((lookup_type == NFT_LOOKUP_ESTABLISHED && (!connected || wildcard)) || 217 (lookup_type == NFT_LOOKUP_LISTENER && connected)) { 218 sock_put(sk); 219 sk = NULL; 220 } 221 } 222 break; 223 default: 224 WARN_ON(1); 225 sk = NULL; 226 } 227 228 pr_debug("tproxy socket lookup: proto %u %pI6:%u -> %pI6:%u, lookup type: %d, sock %p\n", 229 protocol, saddr, ntohs(sport), daddr, ntohs(dport), lookup_type, sk); 230 231 return sk; 232} 233#endif 234 235/** 236 * tproxy_handle_time_wait4 - handle IPv4 TCP TIME_WAIT reopen redirections 237 * @skb: The skb being processed. 238 * @laddr: IPv4 address to redirect to or zero. 239 * @lport: TCP port to redirect to or zero. 240 * @sk: The TIME_WAIT TCP socket found by the lookup. 241 * 242 * We have to handle SYN packets arriving to TIME_WAIT sockets 243 * differently: instead of reopening the connection we should rather 244 * redirect the new connection to the proxy if there's a listener 245 * socket present. 246 * 247 * tproxy_handle_time_wait4() consumes the socket reference passed in. 248 * 249 * Returns the listener socket if there's one, the TIME_WAIT socket if 250 * no such listener is found, or NULL if the TCP header is incomplete. 251 */ 252static struct sock * 253tproxy_handle_time_wait4(struct sk_buff *skb, __be32 laddr, __be16 lport, 254 struct sock *sk) 255{ 256 const struct iphdr *iph = ip_hdr(skb); 257 struct tcphdr _hdr, *hp; 258 259 hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr); 260 if (hp == NULL) { 261 inet_twsk_put(inet_twsk(sk)); 262 return NULL; 263 } 264 265 if (hp->syn && !hp->rst && !hp->ack && !hp->fin) { 266 /* SYN to a TIME_WAIT socket, we'd rather redirect it 267 * to a listener socket if there's one */ 268 struct sock *sk2; 269 270 sk2 = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol, 271 iph->saddr, laddr ? laddr : iph->daddr, 272 hp->source, lport ? lport : hp->dest, 273 skb->dev, NFT_LOOKUP_LISTENER); 274 if (sk2) { 275 inet_twsk_deschedule(inet_twsk(sk)); 276 inet_twsk_put(inet_twsk(sk)); 277 sk = sk2; 278 } 279 } 280 281 return sk; 282} 283 284/* assign a socket to the skb -- consumes sk */ 285static void 286nf_tproxy_assign_sock(struct sk_buff *skb, struct sock *sk) 287{ 288 skb_orphan(skb); 289 skb->sk = sk; 290 skb->destructor = sock_edemux; 291} 292 293static unsigned int 294tproxy_tg4(struct sk_buff *skb, __be32 laddr, __be16 lport, 295 u_int32_t mark_mask, u_int32_t mark_value) 296{ 297 const struct iphdr *iph = ip_hdr(skb); 298 struct udphdr _hdr, *hp; 299 struct sock *sk; 300 301 hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr); 302 if (hp == NULL) 303 return NF_DROP; 304 305 /* check if there's an ongoing connection on the packet 306 * addresses, this happens if the redirect already happened 307 * and the current packet belongs to an already established 308 * connection */ 309 sk = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol, 310 iph->saddr, iph->daddr, 311 hp->source, hp->dest, 312 skb->dev, NFT_LOOKUP_ESTABLISHED); 313 314 laddr = tproxy_laddr4(skb, laddr, iph->daddr); 315 if (!lport) 316 lport = hp->dest; 317 318 /* UDP has no TCP_TIME_WAIT state, so we never enter here */ 319 if (sk && sk->sk_state == TCP_TIME_WAIT) 320 /* reopening a TIME_WAIT connection needs special handling */ 321 sk = tproxy_handle_time_wait4(skb, laddr, lport, sk); 322 else if (!sk) 323 /* no, there's no established connection, check if 324 * there's a listener on the redirected addr/port */ 325 sk = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol, 326 iph->saddr, laddr, 327 hp->source, lport, 328 skb->dev, NFT_LOOKUP_LISTENER); 329 330 /* NOTE: assign_sock consumes our sk reference */ 331 if (sk && tproxy_sk_is_transparent(sk)) { 332 /* This should be in a separate target, but we don't do multiple 333 targets on the same rule yet */ 334 skb->mark = (skb->mark & ~mark_mask) ^ mark_value; 335 336 pr_debug("redirecting: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n", 337 iph->protocol, &iph->daddr, ntohs(hp->dest), 338 &laddr, ntohs(lport), skb->mark); 339 340 nf_tproxy_assign_sock(skb, sk); 341 return NF_ACCEPT; 342 } 343 344 pr_debug("no socket, dropping: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n", 345 iph->protocol, &iph->saddr, ntohs(hp->source), 346 &iph->daddr, ntohs(hp->dest), skb->mark); 347 return NF_DROP; 348} 349 350static unsigned int 351tproxy_tg4_v0(struct sk_buff *skb, const struct xt_action_param *par) 352{ 353 const struct xt_tproxy_target_info *tgi = par->targinfo; 354 355 return tproxy_tg4(skb, tgi->laddr, tgi->lport, tgi->mark_mask, tgi->mark_value); 356} 357 358static unsigned int 359tproxy_tg4_v1(struct sk_buff *skb, const struct xt_action_param *par) 360{ 361 const struct xt_tproxy_target_info_v1 *tgi = par->targinfo; 362 363 return tproxy_tg4(skb, tgi->laddr.ip, tgi->lport, tgi->mark_mask, tgi->mark_value); 364} 365 366#ifdef XT_TPROXY_HAVE_IPV6 367 368static inline const struct in6_addr * 369tproxy_laddr6(struct sk_buff *skb, const struct in6_addr *user_laddr, 370 const struct in6_addr *daddr) 371{ 372 struct inet6_dev *indev; 373 struct inet6_ifaddr *ifa; 374 struct in6_addr *laddr; 375 376 if (!ipv6_addr_any(user_laddr)) 377 return user_laddr; 378 laddr = NULL; 379 380 rcu_read_lock(); 381 indev = __in6_dev_get(skb->dev); 382 if (indev) 383 list_for_each_entry(ifa, &indev->addr_list, if_list) { 384 if (ifa->flags & (IFA_F_TENTATIVE | IFA_F_DEPRECATED)) 385 continue; 386 387 laddr = &ifa->addr; 388 break; 389 } 390 rcu_read_unlock(); 391 392 return laddr ? laddr : daddr; 393} 394 395/** 396 * tproxy_handle_time_wait6 - handle IPv6 TCP TIME_WAIT reopen redirections 397 * @skb: The skb being processed. 398 * @tproto: Transport protocol. 399 * @thoff: Transport protocol header offset. 400 * @par: Iptables target parameters. 401 * @sk: The TIME_WAIT TCP socket found by the lookup. 402 * 403 * We have to handle SYN packets arriving to TIME_WAIT sockets 404 * differently: instead of reopening the connection we should rather 405 * redirect the new connection to the proxy if there's a listener 406 * socket present. 407 * 408 * tproxy_handle_time_wait6() consumes the socket reference passed in. 409 * 410 * Returns the listener socket if there's one, the TIME_WAIT socket if 411 * no such listener is found, or NULL if the TCP header is incomplete. 412 */ 413static struct sock * 414tproxy_handle_time_wait6(struct sk_buff *skb, int tproto, int thoff, 415 const struct xt_action_param *par, 416 struct sock *sk) 417{ 418 const struct ipv6hdr *iph = ipv6_hdr(skb); 419 struct tcphdr _hdr, *hp; 420 const struct xt_tproxy_target_info_v1 *tgi = par->targinfo; 421 422 hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr); 423 if (hp == NULL) { 424 inet_twsk_put(inet_twsk(sk)); 425 return NULL; 426 } 427 428 if (hp->syn && !hp->rst && !hp->ack && !hp->fin) { 429 /* SYN to a TIME_WAIT socket, we'd rather redirect it 430 * to a listener socket if there's one */ 431 struct sock *sk2; 432 433 sk2 = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto, 434 &iph->saddr, 435 tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr), 436 hp->source, 437 tgi->lport ? tgi->lport : hp->dest, 438 skb->dev, NFT_LOOKUP_LISTENER); 439 if (sk2) { 440 inet_twsk_deschedule(inet_twsk(sk)); 441 inet_twsk_put(inet_twsk(sk)); 442 sk = sk2; 443 } 444 } 445 446 return sk; 447} 448 449static unsigned int 450tproxy_tg6_v1(struct sk_buff *skb, const struct xt_action_param *par) 451{ 452 const struct ipv6hdr *iph = ipv6_hdr(skb); 453 const struct xt_tproxy_target_info_v1 *tgi = par->targinfo; 454 struct udphdr _hdr, *hp; 455 struct sock *sk; 456 const struct in6_addr *laddr; 457 __be16 lport; 458 int thoff = 0; 459 int tproto; 460 461 tproto = ipv6_find_hdr(skb, &thoff, -1, NULL, NULL); 462 if (tproto < 0) { 463 pr_debug("unable to find transport header in IPv6 packet, dropping\n"); 464 return NF_DROP; 465 } 466 467 hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr); 468 if (hp == NULL) { 469 pr_debug("unable to grab transport header contents in IPv6 packet, dropping\n"); 470 return NF_DROP; 471 } 472 473 /* check if there's an ongoing connection on the packet 474 * addresses, this happens if the redirect already happened 475 * and the current packet belongs to an already established 476 * connection */ 477 sk = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto, 478 &iph->saddr, &iph->daddr, 479 hp->source, hp->dest, 480 par->in, NFT_LOOKUP_ESTABLISHED); 481 482 laddr = tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr); 483 lport = tgi->lport ? tgi->lport : hp->dest; 484 485 /* UDP has no TCP_TIME_WAIT state, so we never enter here */ 486 if (sk && sk->sk_state == TCP_TIME_WAIT) 487 /* reopening a TIME_WAIT connection needs special handling */ 488 sk = tproxy_handle_time_wait6(skb, tproto, thoff, par, sk); 489 else if (!sk) 490 /* no there's no established connection, check if 491 * there's a listener on the redirected addr/port */ 492 sk = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto, 493 &iph->saddr, laddr, 494 hp->source, lport, 495 par->in, NFT_LOOKUP_LISTENER); 496 497 /* NOTE: assign_sock consumes our sk reference */ 498 if (sk && tproxy_sk_is_transparent(sk)) { 499 /* This should be in a separate target, but we don't do multiple 500 targets on the same rule yet */ 501 skb->mark = (skb->mark & ~tgi->mark_mask) ^ tgi->mark_value; 502 503 pr_debug("redirecting: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n", 504 tproto, &iph->saddr, ntohs(hp->source), 505 laddr, ntohs(lport), skb->mark); 506 507 nf_tproxy_assign_sock(skb, sk); 508 return NF_ACCEPT; 509 } 510 511 pr_debug("no socket, dropping: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n", 512 tproto, &iph->saddr, ntohs(hp->source), 513 &iph->daddr, ntohs(hp->dest), skb->mark); 514 515 return NF_DROP; 516} 517 518static int tproxy_tg6_check(const struct xt_tgchk_param *par) 519{ 520 const struct ip6t_ip6 *i = par->entryinfo; 521 522 if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP) && 523 !(i->invflags & IP6T_INV_PROTO)) 524 return 0; 525 526 pr_info("Can be used only in combination with " 527 "either -p tcp or -p udp\n"); 528 return -EINVAL; 529} 530#endif 531 532static int tproxy_tg4_check(const struct xt_tgchk_param *par) 533{ 534 const struct ipt_ip *i = par->entryinfo; 535 536 if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP) 537 && !(i->invflags & IPT_INV_PROTO)) 538 return 0; 539 540 pr_info("Can be used only in combination with " 541 "either -p tcp or -p udp\n"); 542 return -EINVAL; 543} 544 545static struct xt_target tproxy_tg_reg[] __read_mostly = { 546 { 547 .name = "TPROXY", 548 .family = NFPROTO_IPV4, 549 .table = "mangle", 550 .target = tproxy_tg4_v0, 551 .revision = 0, 552 .targetsize = sizeof(struct xt_tproxy_target_info), 553 .checkentry = tproxy_tg4_check, 554 .hooks = 1 << NF_INET_PRE_ROUTING, 555 .me = THIS_MODULE, 556 }, 557 { 558 .name = "TPROXY", 559 .family = NFPROTO_IPV4, 560 .table = "mangle", 561 .target = tproxy_tg4_v1, 562 .revision = 1, 563 .targetsize = sizeof(struct xt_tproxy_target_info_v1), 564 .checkentry = tproxy_tg4_check, 565 .hooks = 1 << NF_INET_PRE_ROUTING, 566 .me = THIS_MODULE, 567 }, 568#ifdef XT_TPROXY_HAVE_IPV6 569 { 570 .name = "TPROXY", 571 .family = NFPROTO_IPV6, 572 .table = "mangle", 573 .target = tproxy_tg6_v1, 574 .revision = 1, 575 .targetsize = sizeof(struct xt_tproxy_target_info_v1), 576 .checkentry = tproxy_tg6_check, 577 .hooks = 1 << NF_INET_PRE_ROUTING, 578 .me = THIS_MODULE, 579 }, 580#endif 581 582}; 583 584static int __init tproxy_tg_init(void) 585{ 586 nf_defrag_ipv4_enable(); 587#ifdef XT_TPROXY_HAVE_IPV6 588 nf_defrag_ipv6_enable(); 589#endif 590 591 return xt_register_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg)); 592} 593 594static void __exit tproxy_tg_exit(void) 595{ 596 xt_unregister_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg)); 597} 598 599module_init(tproxy_tg_init); 600module_exit(tproxy_tg_exit); 601MODULE_LICENSE("GPL"); 602MODULE_AUTHOR("Balazs Scheidler, Krisztian Kovacs"); 603MODULE_DESCRIPTION("Netfilter transparent proxy (TPROXY) target module."); 604MODULE_ALIAS("ipt_TPROXY"); 605MODULE_ALIAS("ip6t_TPROXY"); 606