net/netfilter/xt_socket.c

   1 /*
   2  * Transparent proxy support for Linux/iptables
   3  *
   4  * Copyright (C) 2007-2008 BalaBit IT Ltd.
   5  * Author: 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/netfilter/x_tables.h>
  16 #include <linux/netfilter_ipv4/ip_tables.h>
  17 #include <net/tcp.h>
  18 #include <net/udp.h>
  19 #include <net/icmp.h>
  20 #include <net/sock.h>
  21 #include <net/inet_sock.h>
  22 #include <net/netfilter/ipv4/nf_defrag_ipv4.h>
  23
  24 #if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
  25 #define XT_SOCKET_HAVE_IPV6 1
  26 #include <linux/netfilter_ipv6/ip6_tables.h>
  27 #include <net/inet6_hashtables.h>
  28 #include <net/netfilter/ipv6/nf_defrag_ipv6.h>
  29 #endif
  30
  31 #include <linux/netfilter/xt_socket.h>
  32
  33 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
  34 #define XT_SOCKET_HAVE_CONNTRACK 1
  35 #include <net/netfilter/nf_conntrack.h>
  36 #endif
  37
  38 static int
  39 extract_icmp4_fields(const struct sk_buff *skb,
  40                     u8 *protocol,
  41                     __be32 *raddr,
  42                     __be32 *laddr,
  43                     __be16 *rport,
  44                     __be16 *lport)
  45 {
  46         unsigned int outside_hdrlen = ip_hdrlen(skb);
  47         struct iphdr *inside_iph, _inside_iph;
  48         struct icmphdr *icmph, _icmph;
  49         __be16 *ports, _ports[2];
  50
  51         icmph = skb_header_pointer(skb, outside_hdrlen,
  52                                    sizeof(_icmph), &_icmph);
  53         if (icmph == NULL)
  54                 return 1;
  55
  56         switch (icmph->type) {
  57         case ICMP_DEST_UNREACH:
  58         case ICMP_SOURCE_QUENCH:
  59         case ICMP_REDIRECT:
  60         case ICMP_TIME_EXCEEDED:
  61         case ICMP_PARAMETERPROB:
  62                 break;
  63         default:
  64                 return 1;
  65         }
  66
  67         inside_iph = skb_header_pointer(skb, outside_hdrlen +
  68                                         sizeof(struct icmphdr),
  69                                         sizeof(_inside_iph), &_inside_iph);
  70         if (inside_iph == NULL)
  71                 return 1;
  72
  73         if (inside_iph->protocol != IPPROTO_TCP &&
  74             inside_iph->protocol != IPPROTO_UDP)
  75                 return 1;
  76
  77         ports = skb_header_pointer(skb, outside_hdrlen +
  78                                    sizeof(struct icmphdr) +
  79                                    (inside_iph->ihl << 2),
  80                                    sizeof(_ports), &_ports);
  81         if (ports == NULL)
  82                 return 1;
  83
  84         /* the inside IP packet is the one quoted from our side, thus
  85          * its saddr is the local address */
  86         *protocol = inside_iph->protocol;
  87         *laddr = inside_iph->saddr;
  88         *lport = ports[0];
  89         *raddr = inside_iph->daddr;
  90         *rport = ports[1];
  91
  92         return 0;
  93 }
  94
  95 /* "socket" match based redirection (no specific rule)
  96  * ===================================================
  97  *
  98  * There are connections with dynamic endpoints (e.g. FTP data
  99  * connection) that the user is unable to add explicit rules
 100  * for. These are taken care of by a generic "socket" rule. It is
 101  * assumed that the proxy application is trusted to open such
 102  * connections without explicit iptables rule (except of course the
 103  * generic 'socket' rule). In this case the following sockets are
 104  * matched in preference order:
 105  *
 106  *   - match: if there's a fully established connection matching the
 107  *     _packet_ tuple
 108  *
 109  *   - match: if there's a non-zero bound listener (possibly with a
 110  *     non-local address) We don't accept zero-bound listeners, since
 111  *     then local services could intercept traffic going through the
 112  *     box.
 113  */
 114 static struct sock *
 115 xt_socket_get_sock_v4(struct net *net, const u8 protocol,
 116                       const __be32 saddr, const __be32 daddr,
 117                       const __be16 sport, const __be16 dport,
 118                       const struct net_device *in)
 119 {
 120         switch (protocol) {
 121         case IPPROTO_TCP:
 122                 return __inet_lookup(net, &tcp_hashinfo,
 123                                      saddr, sport, daddr, dport,
 124                                      in->ifindex);
 125         case IPPROTO_UDP:
 126                 return udp4_lib_lookup(net, saddr, sport, daddr, dport,
 127                                        in->ifindex);
 128         }
 129         return NULL;
 130 }
 131
 132 static bool xt_socket_sk_is_transparent(struct sock *sk)
 133 {
 134         switch (sk->sk_state) {
 135         case TCP_TIME_WAIT:
 136                 return inet_twsk(sk)->tw_transparent;
 137
 138         case TCP_NEW_SYN_RECV:
 139                 return inet_rsk(inet_reqsk(sk))->no_srccheck;
 140
 141         default:
 142                 return inet_sk(sk)->transparent;
 143         }
 144 }
 145
 146 static struct sock *xt_socket_lookup_slow_v4(const struct sk_buff *skb,
 147                                              const struct net_device *indev)
 148 {
 149         const struct iphdr *iph = ip_hdr(skb);
 150         __be32 uninitialized_var(daddr), uninitialized_var(saddr);
 151         __be16 uninitialized_var(dport), uninitialized_var(sport);
 152         u8 uninitialized_var(protocol);
 153 #ifdef XT_SOCKET_HAVE_CONNTRACK
 154         struct nf_conn const *ct;
 155         enum ip_conntrack_info ctinfo;
 156 #endif
 157
 158         if (iph->protocol == IPPROTO_UDP || iph->protocol == IPPROTO_TCP) {
 159                 struct udphdr _hdr, *hp;
 160
 161                 hp = skb_header_pointer(skb, ip_hdrlen(skb),
 162                                         sizeof(_hdr), &_hdr);
 163                 if (hp == NULL)
 164                         return NULL;
 165
 166                 protocol = iph->protocol;
 167                 saddr = iph->saddr;
 168                 sport = hp->source;
 169                 daddr = iph->daddr;
 170                 dport = hp->dest;
 171
 172         } else if (iph->protocol == IPPROTO_ICMP) {
 173                 if (extract_icmp4_fields(skb, &protocol, &saddr, &daddr,
 174                                          &sport, &dport))
 175                         return NULL;
 176         } else {
 177                 return NULL;
 178         }
 179
 180 #ifdef XT_SOCKET_HAVE_CONNTRACK
 181         /* Do the lookup with the original socket address in
 182          * case this is a reply packet of an established
 183          * SNAT-ted connection.
 184          */
 185         ct = nf_ct_get(skb, &ctinfo);
 186         if (ct && !nf_ct_is_untracked(ct) &&
 187             ((iph->protocol != IPPROTO_ICMP &&
 188               ctinfo == IP_CT_ESTABLISHED_REPLY) ||
 189              (iph->protocol == IPPROTO_ICMP &&
 190               ctinfo == IP_CT_RELATED_REPLY)) &&
 191             (ct->status & IPS_SRC_NAT_DONE)) {
 192
 193                 daddr = ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip;
 194                 dport = (iph->protocol == IPPROTO_TCP) ?
 195                         ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u.tcp.port :
 196                         ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u.udp.port;
 197         }
 198 #endif
 199
 200         return xt_socket_get_sock_v4(dev_net(skb->dev), protocol, saddr, daddr,
 201                                      sport, dport, indev);
 202 }
 203
 204 static bool
 205 socket_match(const struct sk_buff *skb, struct xt_action_param *par,
 206              const struct xt_socket_mtinfo1 *info)
 207 {
 208         struct sock *sk = skb->sk;
 209
 210         if (!sk)
 211                 sk = xt_socket_lookup_slow_v4(skb, par->in);
 212         if (sk) {
 213                 bool wildcard;
 214                 bool transparent = true;
 215
 216                 /* Ignore sockets listening on INADDR_ANY,
 217                  * unless XT_SOCKET_NOWILDCARD is set
 218                  */
 219                 wildcard = (!(info->flags & XT_SOCKET_NOWILDCARD) &&
 220                             sk_fullsock(sk) &&
 221                             inet_sk(sk)->inet_rcv_saddr == 0);
 222
 223                 /* Ignore non-transparent sockets,
 224                  * if XT_SOCKET_TRANSPARENT is used
 225                  */
 226                 if (info->flags & XT_SOCKET_TRANSPARENT)
 227                         transparent = xt_socket_sk_is_transparent(sk);
 228
 229                 if (sk != skb->sk)
 230                         sock_gen_put(sk);
 231
 232                 if (wildcard || !transparent)
 233                         sk = NULL;
 234         }
 235
 236         return sk != NULL;
 237 }
 238
 239 static bool
 240 socket_mt4_v0(const struct sk_buff *skb, struct xt_action_param *par)
 241 {
 242         static struct xt_socket_mtinfo1 xt_info_v0 = {
 243                 .flags = 0,
 244         };
 245
 246         return socket_match(skb, par, &xt_info_v0);
 247 }
 248
 249 static bool
 250 socket_mt4_v1_v2(const struct sk_buff *skb, struct xt_action_param *par)
 251 {
 252         return socket_match(skb, par, par->matchinfo);
 253 }
 254
 255 #ifdef XT_SOCKET_HAVE_IPV6
 256
 257 static int
 258 extract_icmp6_fields(const struct sk_buff *skb,
 259                      unsigned int outside_hdrlen,
 260                      int *protocol,
 261                      const struct in6_addr **raddr,
 262                      const struct in6_addr **laddr,
 263                      __be16 *rport,
 264                      __be16 *lport,
 265                      struct ipv6hdr *ipv6_var)
 266 {
 267         const struct ipv6hdr *inside_iph;
 268         struct icmp6hdr *icmph, _icmph;
 269         __be16 *ports, _ports[2];
 270         u8 inside_nexthdr;
 271         __be16 inside_fragoff;
 272         int inside_hdrlen;
 273
 274         icmph = skb_header_pointer(skb, outside_hdrlen,
 275                                    sizeof(_icmph), &_icmph);
 276         if (icmph == NULL)
 277                 return 1;
 278
 279         if (icmph->icmp6_type & ICMPV6_INFOMSG_MASK)
 280                 return 1;
 281
 282         inside_iph = skb_header_pointer(skb, outside_hdrlen + sizeof(_icmph),
 283                                         sizeof(*ipv6_var), ipv6_var);
 284         if (inside_iph == NULL)
 285                 return 1;
 286         inside_nexthdr = inside_iph->nexthdr;
 287
 288         inside_hdrlen = ipv6_skip_exthdr(skb, outside_hdrlen + sizeof(_icmph) +
 289                                               sizeof(*ipv6_var),
 290                                          &inside_nexthdr, &inside_fragoff);
 291         if (inside_hdrlen < 0)
 292                 return 1; /* hjm: Packet has no/incomplete transport layer headers. */
 293
 294         if (inside_nexthdr != IPPROTO_TCP &&
 295             inside_nexthdr != IPPROTO_UDP)
 296                 return 1;
 297
 298         ports = skb_header_pointer(skb, inside_hdrlen,
 299                                    sizeof(_ports), &_ports);
 300         if (ports == NULL)
 301                 return 1;
 302
 303         /* the inside IP packet is the one quoted from our side, thus
 304          * its saddr is the local address */
 305         *protocol = inside_nexthdr;
 306         *laddr = &inside_iph->saddr;
 307         *lport = ports[0];
 308         *raddr = &inside_iph->daddr;
 309         *rport = ports[1];
 310
 311         return 0;
 312 }
 313
 314 static struct sock *
 315 xt_socket_get_sock_v6(struct net *net, const u8 protocol,
 316                       const struct in6_addr *saddr, const struct in6_addr *daddr,
 317                       const __be16 sport, const __be16 dport,
 318                       const struct net_device *in)
 319 {
 320         switch (protocol) {
 321         case IPPROTO_TCP:
 322                 return inet6_lookup(net, &tcp_hashinfo,
 323                                     saddr, sport, daddr, dport,
 324                                     in->ifindex);
 325         case IPPROTO_UDP:
 326                 return udp6_lib_lookup(net, saddr, sport, daddr, dport,
 327                                        in->ifindex);
 328         }
 329
 330         return NULL;
 331 }
 332
 333 static struct sock *xt_socket_lookup_slow_v6(const struct sk_buff *skb,
 334                                              const struct net_device *indev)
 335 {
 336         __be16 uninitialized_var(dport), uninitialized_var(sport);
 337         const struct in6_addr *daddr = NULL, *saddr = NULL;
 338         struct ipv6hdr *iph = ipv6_hdr(skb);
 339         int thoff = 0, tproto;
 340
 341         tproto = ipv6_find_hdr(skb, &thoff, -1, NULL, NULL);
 342         if (tproto < 0) {
 343                 pr_debug("unable to find transport header in IPv6 packet, dropping\n");
 344                 return NULL;
 345         }
 346
 347         if (tproto == IPPROTO_UDP || tproto == IPPROTO_TCP) {
 348                 struct udphdr _hdr, *hp;
 349
 350                 hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
 351                 if (hp == NULL)
 352                         return NULL;
 353
 354                 saddr = &iph->saddr;
 355                 sport = hp->source;
 356                 daddr = &iph->daddr;
 357                 dport = hp->dest;
 358
 359         } else if (tproto == IPPROTO_ICMPV6) {
 360                 struct ipv6hdr ipv6_var;
 361
 362                 if (extract_icmp6_fields(skb, thoff, &tproto, &saddr, &daddr,
 363                                          &sport, &dport, &ipv6_var))
 364                         return NULL;
 365         } else {
 366                 return NULL;
 367         }
 368
 369         return xt_socket_get_sock_v6(dev_net(skb->dev), tproto, saddr, daddr,
 370                                      sport, dport, indev);
 371 }
 372
 373 static bool
 374 socket_mt6_v1_v2(const struct sk_buff *skb, struct xt_action_param *par)
 375 {
 376         const struct xt_socket_mtinfo1 *info = (struct xt_socket_mtinfo1 *) par->matchinfo;
 377         struct sock *sk = skb->sk;
 378
 379         if (!sk)
 380                 sk = xt_socket_lookup_slow_v6(skb, par->in);
 381         if (sk) {
 382                 bool wildcard;
 383                 bool transparent = true;
 384
 385                 /* Ignore sockets listening on INADDR_ANY
 386                  * unless XT_SOCKET_NOWILDCARD is set
 387                  */
 388                 wildcard = (!(info->flags & XT_SOCKET_NOWILDCARD) &&
 389                             sk_fullsock(sk) &&
 390                             ipv6_addr_any(&sk->sk_v6_rcv_saddr));
 391
 392                 /* Ignore non-transparent sockets,
 393                  * if XT_SOCKET_TRANSPARENT is used
 394                  */
 395                 if (info->flags & XT_SOCKET_TRANSPARENT)
 396                         transparent = xt_socket_sk_is_transparent(sk);
 397
 398                 if (sk != skb->sk)
 399                         sock_gen_put(sk);
 400
 401                 if (wildcard || !transparent)
 402                         sk = NULL;
 403         }
 404
 405         return sk != NULL;
 406 }
 407 #endif
 408
 409 static int socket_mt_v1_check(const struct xt_mtchk_param *par)
 410 {
 411         const struct xt_socket_mtinfo1 *info = (struct xt_socket_mtinfo1 *) par->matchinfo;
 412
 413         if (info->flags & ~XT_SOCKET_FLAGS_V1) {
 414                 pr_info("unknown flags 0x%x\n", info->flags & ~XT_SOCKET_FLAGS_V1);
 415                 return -EINVAL;
 416         }
 417         return 0;
 418 }
 419
 420 static int socket_mt_v2_check(const struct xt_mtchk_param *par)
 421 {
 422         const struct xt_socket_mtinfo2 *info = (struct xt_socket_mtinfo2 *) par->matchinfo;
 423
 424         if (info->flags & ~XT_SOCKET_FLAGS_V2) {
 425                 pr_info("unknown flags 0x%x\n", info->flags & ~XT_SOCKET_FLAGS_V2);
 426                 return -EINVAL;
 427         }
 428         return 0;
 429 }
 430
 431 static struct xt_match socket_mt_reg[] __read_mostly = {
 432         {
 433                 .name           = "socket",
 434                 .revision       = 0,
 435                 .family         = NFPROTO_IPV4,
 436                 .match          = socket_mt4_v0,
 437                 .hooks          = (1 << NF_INET_PRE_ROUTING) |
 438                                   (1 << NF_INET_LOCAL_IN),
 439                 .me             = THIS_MODULE,
 440         },
 441         {
 442                 .name           = "socket",
 443                 .revision       = 1,
 444                 .family         = NFPROTO_IPV4,
 445                 .match          = socket_mt4_v1_v2,
 446                 .checkentry     = socket_mt_v1_check,
 447                 .matchsize      = sizeof(struct xt_socket_mtinfo1),
 448                 .hooks          = (1 << NF_INET_PRE_ROUTING) |
 449                                   (1 << NF_INET_LOCAL_IN),
 450                 .me             = THIS_MODULE,
 451         },
 452 #ifdef XT_SOCKET_HAVE_IPV6
 453         {
 454                 .name           = "socket",
 455                 .revision       = 1,
 456                 .family         = NFPROTO_IPV6,
 457                 .match          = socket_mt6_v1_v2,
 458                 .checkentry     = socket_mt_v1_check,
 459                 .matchsize      = sizeof(struct xt_socket_mtinfo1),
 460                 .hooks          = (1 << NF_INET_PRE_ROUTING) |
 461                                   (1 << NF_INET_LOCAL_IN),
 462                 .me             = THIS_MODULE,
 463         },
 464 #endif
 465         {
 466                 .name           = "socket",
 467                 .revision       = 2,
 468                 .family         = NFPROTO_IPV4,
 469                 .match          = socket_mt4_v1_v2,
 470                 .checkentry     = socket_mt_v2_check,
 471                 .matchsize      = sizeof(struct xt_socket_mtinfo1),
 472                 .hooks          = (1 << NF_INET_PRE_ROUTING) |
 473                                   (1 << NF_INET_LOCAL_IN),
 474                 .me             = THIS_MODULE,
 475         },
 476 #ifdef XT_SOCKET_HAVE_IPV6
 477         {
 478                 .name           = "socket",
 479                 .revision       = 2,
 480                 .family         = NFPROTO_IPV6,
 481                 .match          = socket_mt6_v1_v2,
 482                 .checkentry     = socket_mt_v2_check,
 483                 .matchsize      = sizeof(struct xt_socket_mtinfo1),
 484                 .hooks          = (1 << NF_INET_PRE_ROUTING) |
 485                                   (1 << NF_INET_LOCAL_IN),
 486                 .me             = THIS_MODULE,
 487         },
 488 #endif
 489 };
 490
 491 static int __init socket_mt_init(void)
 492 {
 493         nf_defrag_ipv4_enable();
 494 #ifdef XT_SOCKET_HAVE_IPV6
 495         nf_defrag_ipv6_enable();
 496 #endif
 497
 498         return xt_register_matches(socket_mt_reg, ARRAY_SIZE(socket_mt_reg));
 499 }
 500
 501 static void __exit socket_mt_exit(void)
 502 {
 503         xt_unregister_matches(socket_mt_reg, ARRAY_SIZE(socket_mt_reg));
 504 }
 505
 506 module_init(socket_mt_init);
 507 module_exit(socket_mt_exit);
 508
 509 MODULE_LICENSE("GPL");
 510 MODULE_AUTHOR("Krisztian Kovacs, Balazs Scheidler");
 511 MODULE_DESCRIPTION("x_tables socket match module");
 512 MODULE_ALIAS("ipt_socket");
 513 MODULE_ALIAS("ip6t_socket");