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 38 enum nf_tproxy_lookup_t { 39 NFT_LOOKUP_LISTENER, 40 NFT_LOOKUP_ESTABLISHED, 41 }; 42 43 static 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 63 static inline __be32 64 tproxy_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 */ 107 static inline struct sock * 108 nf_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 171 static inline struct sock * 172 nf_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 */ 252 static struct sock * 253 tproxy_handle_time_wait4(struct net *net, struct sk_buff *skb, 254 __be32 laddr, __be16 lport, 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(net, 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_put(inet_twsk(sk)); 276 sk = sk2; 277 } 278 } 279 280 return sk; 281 } 282 283 /* assign a socket to the skb -- consumes sk */ 284 static void 285 nf_tproxy_assign_sock(struct sk_buff *skb, struct sock *sk) 286 { 287 skb_orphan(skb); 288 skb->sk = sk; 289 skb->destructor = sock_edemux; 290 } 291 292 static unsigned int 293 tproxy_tg4(struct net *net, struct sk_buff *skb, __be32 laddr, __be16 lport, 294 u_int32_t mark_mask, u_int32_t mark_value) 295 { 296 const struct iphdr *iph = ip_hdr(skb); 297 struct udphdr _hdr, *hp; 298 struct sock *sk; 299 300 hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr); 301 if (hp == NULL) 302 return NF_DROP; 303 304 /* check if there's an ongoing connection on the packet 305 * addresses, this happens if the redirect already happened 306 * and the current packet belongs to an already established 307 * connection */ 308 sk = nf_tproxy_get_sock_v4(net, iph->protocol, 309 iph->saddr, iph->daddr, 310 hp->source, hp->dest, 311 skb->dev, NFT_LOOKUP_ESTABLISHED); 312 313 laddr = tproxy_laddr4(skb, laddr, iph->daddr); 314 if (!lport) 315 lport = hp->dest; 316 317 /* UDP has no TCP_TIME_WAIT state, so we never enter here */ 318 if (sk && sk->sk_state == TCP_TIME_WAIT) 319 /* reopening a TIME_WAIT connection needs special handling */ 320 sk = tproxy_handle_time_wait4(net, skb, laddr, lport, sk); 321 else if (!sk) 322 /* no, there's no established connection, check if 323 * there's a listener on the redirected addr/port */ 324 sk = nf_tproxy_get_sock_v4(net, iph->protocol, 325 iph->saddr, laddr, 326 hp->source, lport, 327 skb->dev, NFT_LOOKUP_LISTENER); 328 329 /* NOTE: assign_sock consumes our sk reference */ 330 if (sk && tproxy_sk_is_transparent(sk)) { 331 /* This should be in a separate target, but we don't do multiple 332 targets on the same rule yet */ 333 skb->mark = (skb->mark & ~mark_mask) ^ mark_value; 334 335 pr_debug("redirecting: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n", 336 iph->protocol, &iph->daddr, ntohs(hp->dest), 337 &laddr, ntohs(lport), skb->mark); 338 339 nf_tproxy_assign_sock(skb, sk); 340 return NF_ACCEPT; 341 } 342 343 pr_debug("no socket, dropping: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n", 344 iph->protocol, &iph->saddr, ntohs(hp->source), 345 &iph->daddr, ntohs(hp->dest), skb->mark); 346 return NF_DROP; 347 } 348 349 static unsigned int 350 tproxy_tg4_v0(struct sk_buff *skb, const struct xt_action_param *par) 351 { 352 const struct xt_tproxy_target_info *tgi = par->targinfo; 353 354 return tproxy_tg4(par->net, skb, tgi->laddr, tgi->lport, tgi->mark_mask, tgi->mark_value); 355 } 356 357 static unsigned int 358 tproxy_tg4_v1(struct sk_buff *skb, const struct xt_action_param *par) 359 { 360 const struct xt_tproxy_target_info_v1 *tgi = par->targinfo; 361 362 return tproxy_tg4(par->net, skb, tgi->laddr.ip, tgi->lport, tgi->mark_mask, tgi->mark_value); 363 } 364 365 #ifdef XT_TPROXY_HAVE_IPV6 366 367 static inline const struct in6_addr * 368 tproxy_laddr6(struct sk_buff *skb, const struct in6_addr *user_laddr, 369 const struct in6_addr *daddr) 370 { 371 struct inet6_dev *indev; 372 struct inet6_ifaddr *ifa; 373 struct in6_addr *laddr; 374 375 if (!ipv6_addr_any(user_laddr)) 376 return user_laddr; 377 laddr = NULL; 378 379 rcu_read_lock(); 380 indev = __in6_dev_get(skb->dev); 381 if (indev) 382 list_for_each_entry(ifa, &indev->addr_list, if_list) { 383 if (ifa->flags & (IFA_F_TENTATIVE | IFA_F_DEPRECATED)) 384 continue; 385 386 laddr = &ifa->addr; 387 break; 388 } 389 rcu_read_unlock(); 390 391 return laddr ? laddr : daddr; 392 } 393 394 /** 395 * tproxy_handle_time_wait6 - handle IPv6 TCP TIME_WAIT reopen redirections 396 * @skb: The skb being processed. 397 * @tproto: Transport protocol. 398 * @thoff: Transport protocol header offset. 399 * @par: Iptables target parameters. 400 * @sk: The TIME_WAIT TCP socket found by the lookup. 401 * 402 * We have to handle SYN packets arriving to TIME_WAIT sockets 403 * differently: instead of reopening the connection we should rather 404 * redirect the new connection to the proxy if there's a listener 405 * socket present. 406 * 407 * tproxy_handle_time_wait6() consumes the socket reference passed in. 408 * 409 * Returns the listener socket if there's one, the TIME_WAIT socket if 410 * no such listener is found, or NULL if the TCP header is incomplete. 411 */ 412 static struct sock * 413 tproxy_handle_time_wait6(struct sk_buff *skb, int tproto, int thoff, 414 const struct xt_action_param *par, 415 struct sock *sk) 416 { 417 const struct ipv6hdr *iph = ipv6_hdr(skb); 418 struct tcphdr _hdr, *hp; 419 const struct xt_tproxy_target_info_v1 *tgi = par->targinfo; 420 421 hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr); 422 if (hp == NULL) { 423 inet_twsk_put(inet_twsk(sk)); 424 return NULL; 425 } 426 427 if (hp->syn && !hp->rst && !hp->ack && !hp->fin) { 428 /* SYN to a TIME_WAIT socket, we'd rather redirect it 429 * to a listener socket if there's one */ 430 struct sock *sk2; 431 432 sk2 = nf_tproxy_get_sock_v6(par->net, tproto, 433 &iph->saddr, 434 tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr), 435 hp->source, 436 tgi->lport ? tgi->lport : hp->dest, 437 skb->dev, NFT_LOOKUP_LISTENER); 438 if (sk2) { 439 inet_twsk_deschedule_put(inet_twsk(sk)); 440 sk = sk2; 441 } 442 } 443 444 return sk; 445 } 446 447 static unsigned int 448 tproxy_tg6_v1(struct sk_buff *skb, const struct xt_action_param *par) 449 { 450 const struct ipv6hdr *iph = ipv6_hdr(skb); 451 const struct xt_tproxy_target_info_v1 *tgi = par->targinfo; 452 struct udphdr _hdr, *hp; 453 struct sock *sk; 454 const struct in6_addr *laddr; 455 __be16 lport; 456 int thoff = 0; 457 int tproto; 458 459 tproto = ipv6_find_hdr(skb, &thoff, -1, NULL, NULL); 460 if (tproto < 0) { 461 pr_debug("unable to find transport header in IPv6 packet, dropping\n"); 462 return NF_DROP; 463 } 464 465 hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr); 466 if (hp == NULL) { 467 pr_debug("unable to grab transport header contents in IPv6 packet, dropping\n"); 468 return NF_DROP; 469 } 470 471 /* check if there's an ongoing connection on the packet 472 * addresses, this happens if the redirect already happened 473 * and the current packet belongs to an already established 474 * connection */ 475 sk = nf_tproxy_get_sock_v6(par->net, tproto, 476 &iph->saddr, &iph->daddr, 477 hp->source, hp->dest, 478 par->in, NFT_LOOKUP_ESTABLISHED); 479 480 laddr = tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr); 481 lport = tgi->lport ? tgi->lport : hp->dest; 482 483 /* UDP has no TCP_TIME_WAIT state, so we never enter here */ 484 if (sk && sk->sk_state == TCP_TIME_WAIT) 485 /* reopening a TIME_WAIT connection needs special handling */ 486 sk = tproxy_handle_time_wait6(skb, tproto, thoff, par, sk); 487 else if (!sk) 488 /* no there's no established connection, check if 489 * there's a listener on the redirected addr/port */ 490 sk = nf_tproxy_get_sock_v6(par->net, tproto, 491 &iph->saddr, laddr, 492 hp->source, lport, 493 par->in, NFT_LOOKUP_LISTENER); 494 495 /* NOTE: assign_sock consumes our sk reference */ 496 if (sk && tproxy_sk_is_transparent(sk)) { 497 /* This should be in a separate target, but we don't do multiple 498 targets on the same rule yet */ 499 skb->mark = (skb->mark & ~tgi->mark_mask) ^ tgi->mark_value; 500 501 pr_debug("redirecting: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n", 502 tproto, &iph->saddr, ntohs(hp->source), 503 laddr, ntohs(lport), skb->mark); 504 505 nf_tproxy_assign_sock(skb, sk); 506 return NF_ACCEPT; 507 } 508 509 pr_debug("no socket, dropping: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n", 510 tproto, &iph->saddr, ntohs(hp->source), 511 &iph->daddr, ntohs(hp->dest), skb->mark); 512 513 return NF_DROP; 514 } 515 516 static int tproxy_tg6_check(const struct xt_tgchk_param *par) 517 { 518 const struct ip6t_ip6 *i = par->entryinfo; 519 520 if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP) && 521 !(i->invflags & IP6T_INV_PROTO)) 522 return 0; 523 524 pr_info("Can be used only in combination with " 525 "either -p tcp or -p udp\n"); 526 return -EINVAL; 527 } 528 #endif 529 530 static int tproxy_tg4_check(const struct xt_tgchk_param *par) 531 { 532 const struct ipt_ip *i = par->entryinfo; 533 534 if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP) 535 && !(i->invflags & IPT_INV_PROTO)) 536 return 0; 537 538 pr_info("Can be used only in combination with " 539 "either -p tcp or -p udp\n"); 540 return -EINVAL; 541 } 542 543 static struct xt_target tproxy_tg_reg[] __read_mostly = { 544 { 545 .name = "TPROXY", 546 .family = NFPROTO_IPV4, 547 .table = "mangle", 548 .target = tproxy_tg4_v0, 549 .revision = 0, 550 .targetsize = sizeof(struct xt_tproxy_target_info), 551 .checkentry = tproxy_tg4_check, 552 .hooks = 1 << NF_INET_PRE_ROUTING, 553 .me = THIS_MODULE, 554 }, 555 { 556 .name = "TPROXY", 557 .family = NFPROTO_IPV4, 558 .table = "mangle", 559 .target = tproxy_tg4_v1, 560 .revision = 1, 561 .targetsize = sizeof(struct xt_tproxy_target_info_v1), 562 .checkentry = tproxy_tg4_check, 563 .hooks = 1 << NF_INET_PRE_ROUTING, 564 .me = THIS_MODULE, 565 }, 566 #ifdef XT_TPROXY_HAVE_IPV6 567 { 568 .name = "TPROXY", 569 .family = NFPROTO_IPV6, 570 .table = "mangle", 571 .target = tproxy_tg6_v1, 572 .revision = 1, 573 .targetsize = sizeof(struct xt_tproxy_target_info_v1), 574 .checkentry = tproxy_tg6_check, 575 .hooks = 1 << NF_INET_PRE_ROUTING, 576 .me = THIS_MODULE, 577 }, 578 #endif 579 580 }; 581 582 static int __init tproxy_tg_init(void) 583 { 584 nf_defrag_ipv4_enable(); 585 #ifdef XT_TPROXY_HAVE_IPV6 586 nf_defrag_ipv6_enable(); 587 #endif 588 589 return xt_register_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg)); 590 } 591 592 static void __exit tproxy_tg_exit(void) 593 { 594 xt_unregister_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg)); 595 } 596 597 module_init(tproxy_tg_init); 598 module_exit(tproxy_tg_exit); 599 MODULE_LICENSE("GPL"); 600 MODULE_AUTHOR("Balazs Scheidler, Krisztian Kovacs"); 601 MODULE_DESCRIPTION("Netfilter transparent proxy (TPROXY) target module."); 602 MODULE_ALIAS("ipt_TPROXY"); 603 MODULE_ALIAS("ip6t_TPROXY"); 604