net/netfilter/xt_TPROXY.c

   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/inet_sock.h>
  19 #include <linux/inetdevice.h>
  20 #include <linux/netfilter/x_tables.h>
  21 #include <linux/netfilter_ipv4/ip_tables.h>
  22
  23 #include <net/netfilter/ipv4/nf_defrag_ipv4.h>
  24
  25 #if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
  26 #define XT_TPROXY_HAVE_IPV6 1
  27 #include <net/if_inet6.h>
  28 #include <net/addrconf.h>
  29 #include <linux/netfilter_ipv6/ip6_tables.h>
  30 #include <net/netfilter/ipv6/nf_defrag_ipv6.h>
  31 #endif
  32
  33 #include <net/netfilter/nf_tproxy_core.h>
  34 #include <linux/netfilter/xt_TPROXY.h>
  35
  36 static bool tproxy_sk_is_transparent(struct sock *sk)
  37 {
  38         if (sk->sk_state != TCP_TIME_WAIT) {
  39                 if (inet_sk(sk)->transparent)
  40                         return true;
  41                 sock_put(sk);
  42         } else {
  43                 if (inet_twsk(sk)->tw_transparent)
  44                         return true;
  45                 inet_twsk_put(inet_twsk(sk));
  46         }
  47         return false;
  48 }
  49
  50 static inline __be32
  51 tproxy_laddr4(struct sk_buff *skb, __be32 user_laddr, __be32 daddr)
  52 {
  53         struct in_device *indev;
  54         __be32 laddr;
  55
  56         if (user_laddr)
  57                 return user_laddr;
  58
  59         laddr = 0;
  60         rcu_read_lock();
  61         indev = __in_dev_get_rcu(skb->dev);
  62         for_primary_ifa(indev) {
  63                 laddr = ifa->ifa_local;
  64                 break;
  65         } endfor_ifa(indev);
  66         rcu_read_unlock();
  67
  68         return laddr ? laddr : daddr;
  69 }
  70
  71 /**
  72  * tproxy_handle_time_wait4 - handle IPv4 TCP TIME_WAIT reopen redirections
  73  * @skb:        The skb being processed.
  74  * @laddr:      IPv4 address to redirect to or zero.
  75  * @lport:      TCP port to redirect to or zero.
  76  * @sk:         The TIME_WAIT TCP socket found by the lookup.
  77  *
  78  * We have to handle SYN packets arriving to TIME_WAIT sockets
  79  * differently: instead of reopening the connection we should rather
  80  * redirect the new connection to the proxy if there's a listener
  81  * socket present.
  82  *
  83  * tproxy_handle_time_wait4() consumes the socket reference passed in.
  84  *
  85  * Returns the listener socket if there's one, the TIME_WAIT socket if
  86  * no such listener is found, or NULL if the TCP header is incomplete.
  87  */
  88 static struct sock *
  89 tproxy_handle_time_wait4(struct sk_buff *skb, __be32 laddr, __be16 lport,
  90                         struct sock *sk)
  91 {
  92         const struct iphdr *iph = ip_hdr(skb);
  93         struct tcphdr _hdr, *hp;
  94
  95         hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
  96         if (hp == NULL) {
  97                 inet_twsk_put(inet_twsk(sk));
  98                 return NULL;
  99         }
 100
 101         if (hp->syn && !hp->rst && !hp->ack && !hp->fin) {
 102                 /* SYN to a TIME_WAIT socket, we'd rather redirect it
 103                  * to a listener socket if there's one */
 104                 struct sock *sk2;
 105
 106                 sk2 = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
 107                                             iph->saddr, laddr ? laddr : iph->daddr,
 108                                             hp->source, lport ? lport : hp->dest,
 109                                             skb->dev, NFT_LOOKUP_LISTENER);
 110                 if (sk2) {
 111                         inet_twsk_deschedule(inet_twsk(sk), &tcp_death_row);
 112                         inet_twsk_put(inet_twsk(sk));
 113                         sk = sk2;
 114                 }
 115         }
 116
 117         return sk;
 118 }
 119
 120 static unsigned int
 121 tproxy_tg4(struct sk_buff *skb, __be32 laddr, __be16 lport,
 122            u_int32_t mark_mask, u_int32_t mark_value)
 123 {
 124         const struct iphdr *iph = ip_hdr(skb);
 125         struct udphdr _hdr, *hp;
 126         struct sock *sk;
 127
 128         hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
 129         if (hp == NULL)
 130                 return NF_DROP;
 131
 132         /* check if there's an ongoing connection on the packet
 133          * addresses, this happens if the redirect already happened
 134          * and the current packet belongs to an already established
 135          * connection */
 136         sk = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
 137                                    iph->saddr, iph->daddr,
 138                                    hp->source, hp->dest,
 139                                    skb->dev, NFT_LOOKUP_ESTABLISHED);
 140
 141         laddr = tproxy_laddr4(skb, laddr, iph->daddr);
 142         if (!lport)
 143                 lport = hp->dest;
 144
 145         /* UDP has no TCP_TIME_WAIT state, so we never enter here */
 146         if (sk && sk->sk_state == TCP_TIME_WAIT)
 147                 /* reopening a TIME_WAIT connection needs special handling */
 148                 sk = tproxy_handle_time_wait4(skb, laddr, lport, sk);
 149         else if (!sk)
 150                 /* no, there's no established connection, check if
 151                  * there's a listener on the redirected addr/port */
 152                 sk = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
 153                                            iph->saddr, laddr,
 154                                            hp->source, lport,
 155                                            skb->dev, NFT_LOOKUP_LISTENER);
 156
 157         /* NOTE: assign_sock consumes our sk reference */
 158         if (sk && tproxy_sk_is_transparent(sk)) {
 159                 /* This should be in a separate target, but we don't do multiple
 160                    targets on the same rule yet */
 161                 skb->mark = (skb->mark & ~mark_mask) ^ mark_value;
 162
 163                 pr_debug("redirecting: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n",
 164                          iph->protocol, &iph->daddr, ntohs(hp->dest),
 165                          &laddr, ntohs(lport), skb->mark);
 166
 167                 nf_tproxy_assign_sock(skb, sk);
 168                 return NF_ACCEPT;
 169         }
 170
 171         pr_debug("no socket, dropping: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n",
 172                  iph->protocol, &iph->saddr, ntohs(hp->source),
 173                  &iph->daddr, ntohs(hp->dest), skb->mark);
 174         return NF_DROP;
 175 }
 176
 177 static unsigned int
 178 tproxy_tg4_v0(struct sk_buff *skb, const struct xt_action_param *par)
 179 {
 180         const struct xt_tproxy_target_info *tgi = par->targinfo;
 181
 182         return tproxy_tg4(skb, tgi->laddr, tgi->lport, tgi->mark_mask, tgi->mark_value);
 183 }
 184
 185 static unsigned int
 186 tproxy_tg4_v1(struct sk_buff *skb, const struct xt_action_param *par)
 187 {
 188         const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
 189
 190         return tproxy_tg4(skb, tgi->laddr.ip, tgi->lport, tgi->mark_mask, tgi->mark_value);
 191 }
 192
 193 #ifdef XT_TPROXY_HAVE_IPV6
 194
 195 static inline const struct in6_addr *
 196 tproxy_laddr6(struct sk_buff *skb, const struct in6_addr *user_laddr,
 197               const struct in6_addr *daddr)
 198 {
 199         struct inet6_dev *indev;
 200         struct inet6_ifaddr *ifa;
 201         struct in6_addr *laddr;
 202
 203         if (!ipv6_addr_any(user_laddr))
 204                 return user_laddr;
 205         laddr = NULL;
 206
 207         rcu_read_lock();
 208         indev = __in6_dev_get(skb->dev);
 209         if (indev)
 210                 list_for_each_entry(ifa, &indev->addr_list, if_list) {
 211                         if (ifa->flags & (IFA_F_TENTATIVE | IFA_F_DEPRECATED))
 212                                 continue;
 213
 214                         laddr = &ifa->addr;
 215                         break;
 216                 }
 217         rcu_read_unlock();
 218
 219         return laddr ? laddr : daddr;
 220 }
 221
 222 /**
 223  * tproxy_handle_time_wait6 - handle IPv6 TCP TIME_WAIT reopen redirections
 224  * @skb:        The skb being processed.
 225  * @tproto:     Transport protocol.
 226  * @thoff:      Transport protocol header offset.
 227  * @par:        Iptables target parameters.
 228  * @sk:         The TIME_WAIT TCP socket found by the lookup.
 229  *
 230  * We have to handle SYN packets arriving to TIME_WAIT sockets
 231  * differently: instead of reopening the connection we should rather
 232  * redirect the new connection to the proxy if there's a listener
 233  * socket present.
 234  *
 235  * tproxy_handle_time_wait6() consumes the socket reference passed in.
 236  *
 237  * Returns the listener socket if there's one, the TIME_WAIT socket if
 238  * no such listener is found, or NULL if the TCP header is incomplete.
 239  */
 240 static struct sock *
 241 tproxy_handle_time_wait6(struct sk_buff *skb, int tproto, int thoff,
 242                          const struct xt_action_param *par,
 243                          struct sock *sk)
 244 {
 245         const struct ipv6hdr *iph = ipv6_hdr(skb);
 246         struct tcphdr _hdr, *hp;
 247         const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
 248
 249         hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
 250         if (hp == NULL) {
 251                 inet_twsk_put(inet_twsk(sk));
 252                 return NULL;
 253         }
 254
 255         if (hp->syn && !hp->rst && !hp->ack && !hp->fin) {
 256                 /* SYN to a TIME_WAIT socket, we'd rather redirect it
 257                  * to a listener socket if there's one */
 258                 struct sock *sk2;
 259
 260                 sk2 = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto,
 261                                             &iph->saddr,
 262                                             tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr),
 263                                             hp->source,
 264                                             tgi->lport ? tgi->lport : hp->dest,
 265                                             skb->dev, NFT_LOOKUP_LISTENER);
 266                 if (sk2) {
 267                         inet_twsk_deschedule(inet_twsk(sk), &tcp_death_row);
 268                         inet_twsk_put(inet_twsk(sk));
 269                         sk = sk2;
 270                 }
 271         }
 272
 273         return sk;
 274 }
 275
 276 static unsigned int
 277 tproxy_tg6_v1(struct sk_buff *skb, const struct xt_action_param *par)
 278 {
 279         const struct ipv6hdr *iph = ipv6_hdr(skb);
 280         const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
 281         struct udphdr _hdr, *hp;
 282         struct sock *sk;
 283         const struct in6_addr *laddr;
 284         __be16 lport;
 285         int thoff = 0;
 286         int tproto;
 287
 288         tproto = ipv6_find_hdr(skb, &thoff, -1, NULL, NULL);
 289         if (tproto < 0) {
 290                 pr_debug("unable to find transport header in IPv6 packet, dropping\n");
 291                 return NF_DROP;
 292         }
 293
 294         hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
 295         if (hp == NULL) {
 296                 pr_debug("unable to grab transport header contents in IPv6 packet, dropping\n");
 297                 return NF_DROP;
 298         }
 299
 300         /* check if there's an ongoing connection on the packet
 301          * addresses, this happens if the redirect already happened
 302          * and the current packet belongs to an already established
 303          * connection */
 304         sk = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto,
 305                                    &iph->saddr, &iph->daddr,
 306                                    hp->source, hp->dest,
 307                                    par->in, NFT_LOOKUP_ESTABLISHED);
 308
 309         laddr = tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr);
 310         lport = tgi->lport ? tgi->lport : hp->dest;
 311
 312         /* UDP has no TCP_TIME_WAIT state, so we never enter here */
 313         if (sk && sk->sk_state == TCP_TIME_WAIT)
 314                 /* reopening a TIME_WAIT connection needs special handling */
 315                 sk = tproxy_handle_time_wait6(skb, tproto, thoff, par, sk);
 316         else if (!sk)
 317                 /* no there's no established connection, check if
 318                  * there's a listener on the redirected addr/port */
 319                 sk = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto,
 320                                            &iph->saddr, laddr,
 321                                            hp->source, lport,
 322                                            par->in, NFT_LOOKUP_LISTENER);
 323
 324         /* NOTE: assign_sock consumes our sk reference */
 325         if (sk && tproxy_sk_is_transparent(sk)) {
 326                 /* This should be in a separate target, but we don't do multiple
 327                    targets on the same rule yet */
 328                 skb->mark = (skb->mark & ~tgi->mark_mask) ^ tgi->mark_value;
 329
 330                 pr_debug("redirecting: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n",
 331                          tproto, &iph->saddr, ntohs(hp->source),
 332                          laddr, ntohs(lport), skb->mark);
 333
 334                 nf_tproxy_assign_sock(skb, sk);
 335                 return NF_ACCEPT;
 336         }
 337
 338         pr_debug("no socket, dropping: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n",
 339                  tproto, &iph->saddr, ntohs(hp->source),
 340                  &iph->daddr, ntohs(hp->dest), skb->mark);
 341
 342         return NF_DROP;
 343 }
 344
 345 static int tproxy_tg6_check(const struct xt_tgchk_param *par)
 346 {
 347         const struct ip6t_ip6 *i = par->entryinfo;
 348
 349         if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP)
 350             && !(i->flags & IP6T_INV_PROTO))
 351                 return 0;
 352
 353         pr_info("Can be used only in combination with "
 354                 "either -p tcp or -p udp\n");
 355         return -EINVAL;
 356 }
 357 #endif
 358
 359 static int tproxy_tg4_check(const struct xt_tgchk_param *par)
 360 {
 361         const struct ipt_ip *i = par->entryinfo;
 362
 363         if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP)
 364             && !(i->invflags & IPT_INV_PROTO))
 365                 return 0;
 366
 367         pr_info("Can be used only in combination with "
 368                 "either -p tcp or -p udp\n");
 369         return -EINVAL;
 370 }
 371
 372 static struct xt_target tproxy_tg_reg[] __read_mostly = {
 373         {
 374                 .name           = "TPROXY",
 375                 .family         = NFPROTO_IPV4,
 376                 .table          = "mangle",
 377                 .target         = tproxy_tg4_v0,
 378                 .revision       = 0,
 379                 .targetsize     = sizeof(struct xt_tproxy_target_info),
 380                 .checkentry     = tproxy_tg4_check,
 381                 .hooks          = 1 << NF_INET_PRE_ROUTING,
 382                 .me             = THIS_MODULE,
 383         },
 384         {
 385                 .name           = "TPROXY",
 386                 .family         = NFPROTO_IPV4,
 387                 .table          = "mangle",
 388                 .target         = tproxy_tg4_v1,
 389                 .revision       = 1,
 390                 .targetsize     = sizeof(struct xt_tproxy_target_info_v1),
 391                 .checkentry     = tproxy_tg4_check,
 392                 .hooks          = 1 << NF_INET_PRE_ROUTING,
 393                 .me             = THIS_MODULE,
 394         },
 395 #ifdef XT_TPROXY_HAVE_IPV6
 396         {
 397                 .name           = "TPROXY",
 398                 .family         = NFPROTO_IPV6,
 399                 .table          = "mangle",
 400                 .target         = tproxy_tg6_v1,
 401                 .revision       = 1,
 402                 .targetsize     = sizeof(struct xt_tproxy_target_info_v1),
 403                 .checkentry     = tproxy_tg6_check,
 404                 .hooks          = 1 << NF_INET_PRE_ROUTING,
 405                 .me             = THIS_MODULE,
 406         },
 407 #endif
 408
 409 };
 410
 411 static int __init tproxy_tg_init(void)
 412 {
 413         nf_defrag_ipv4_enable();
 414 #ifdef XT_TPROXY_HAVE_IPV6
 415         nf_defrag_ipv6_enable();
 416 #endif
 417
 418         return xt_register_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg));
 419 }
 420
 421 static void __exit tproxy_tg_exit(void)
 422 {
 423         xt_unregister_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg));
 424 }
 425
 426 module_init(tproxy_tg_init);
 427 module_exit(tproxy_tg_exit);
 428 MODULE_LICENSE("GPL");
 429 MODULE_AUTHOR("Balazs Scheidler, Krisztian Kovacs");
 430 MODULE_DESCRIPTION("Netfilter transparent proxy (TPROXY) target module.");
 431 MODULE_ALIAS("ipt_TPROXY");
 432 MODULE_ALIAS("ip6t_TPROXY");