net/ipv4/netfilter/nf_nat_sip.c

   1 /* SIP extension for UDP NAT alteration.
   2  *
   3  * (C) 2005 by Christian Hentschel <chentschel@arnet.com.ar>
   4  * based on RR's ip_nat_ftp.c and other modules.
   5  * (C) 2007 United Security Providers
   6  * (C) 2007, 2008 Patrick McHardy <kaber@trash.net>
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License version 2 as
  10  * published by the Free Software Foundation.
  11  */
  12
  13 #include <linux/module.h>
  14 #include <linux/skbuff.h>
  15 #include <linux/ip.h>
  16 #include <net/ip.h>
  17 #include <linux/udp.h>
  18
  19 #include <net/netfilter/nf_nat.h>
  20 #include <net/netfilter/nf_nat_helper.h>
  21 #include <net/netfilter/nf_nat_rule.h>
  22 #include <net/netfilter/nf_conntrack_helper.h>
  23 #include <net/netfilter/nf_conntrack_expect.h>
  24 #include <linux/netfilter/nf_conntrack_sip.h>
  25
  26 MODULE_LICENSE("GPL");
  27 MODULE_AUTHOR("Christian Hentschel <chentschel@arnet.com.ar>");
  28 MODULE_DESCRIPTION("SIP NAT helper");
  29 MODULE_ALIAS("ip_nat_sip");
  30
  31
  32 static unsigned int mangle_packet(struct sk_buff *skb, unsigned int dataoff,
  33                                   const char **dptr, unsigned int *datalen,
  34                                   unsigned int matchoff, unsigned int matchlen,
  35                                   const char *buffer, unsigned int buflen)
  36 {
  37         enum ip_conntrack_info ctinfo;
  38         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
  39
  40         if (!nf_nat_mangle_udp_packet(skb, ct, ctinfo, matchoff, matchlen,
  41                                       buffer, buflen))
  42                 return 0;
  43
  44         /* Reload data pointer and adjust datalen value */
  45         *dptr = skb->data + dataoff;
  46         *datalen += buflen - matchlen;
  47         return 1;
  48 }
  49
  50 static int map_addr(struct sk_buff *skb, unsigned int dataoff,
  51                     const char **dptr, unsigned int *datalen,
  52                     unsigned int matchoff, unsigned int matchlen,
  53                     union nf_inet_addr *addr, __be16 port)
  54 {
  55         enum ip_conntrack_info ctinfo;
  56         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
  57         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
  58         char buffer[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
  59         unsigned int buflen;
  60         __be32 newaddr;
  61         __be16 newport;
  62
  63         if (ct->tuplehash[dir].tuple.src.u3.ip == addr->ip &&
  64             ct->tuplehash[dir].tuple.src.u.udp.port == port) {
  65                 newaddr = ct->tuplehash[!dir].tuple.dst.u3.ip;
  66                 newport = ct->tuplehash[!dir].tuple.dst.u.udp.port;
  67         } else if (ct->tuplehash[dir].tuple.dst.u3.ip == addr->ip &&
  68                    ct->tuplehash[dir].tuple.dst.u.udp.port == port) {
  69                 newaddr = ct->tuplehash[!dir].tuple.src.u3.ip;
  70                 newport = ct->tuplehash[!dir].tuple.src.u.udp.port;
  71         } else
  72                 return 1;
  73
  74         if (newaddr == addr->ip && newport == port)
  75                 return 1;
  76
  77         buflen = sprintf(buffer, "%pI4:%u", &newaddr, ntohs(newport));
  78
  79         return mangle_packet(skb, dataoff, dptr, datalen, matchoff, matchlen,
  80                              buffer, buflen);
  81 }
  82
  83 static int map_sip_addr(struct sk_buff *skb, unsigned int dataoff,
  84                         const char **dptr, unsigned int *datalen,
  85                         enum sip_header_types type)
  86 {
  87         enum ip_conntrack_info ctinfo;
  88         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
  89         unsigned int matchlen, matchoff;
  90         union nf_inet_addr addr;
  91         __be16 port;
  92
  93         if (ct_sip_parse_header_uri(ct, *dptr, NULL, *datalen, type, NULL,
  94                                     &matchoff, &matchlen, &addr, &port) <= 0)
  95                 return 1;
  96         return map_addr(skb, dataoff, dptr, datalen, matchoff, matchlen,
  97                         &addr, port);
  98 }
  99
 100 static unsigned int ip_nat_sip(struct sk_buff *skb, unsigned int dataoff,
 101                                const char **dptr, unsigned int *datalen)
 102 {
 103         enum ip_conntrack_info ctinfo;
 104         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 105         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 106         unsigned int coff, matchoff, matchlen;
 107         union nf_inet_addr addr;
 108         __be16 port;
 109         int request, in_header;
 110
 111         /* Basic rules: requests and responses. */
 112         if (strnicmp(*dptr, "SIP/2.0", strlen("SIP/2.0")) != 0) {
 113                 if (ct_sip_parse_request(ct, *dptr, *datalen,
 114                                          &matchoff, &matchlen,
 115                                          &addr, &port) > 0 &&
 116                     !map_addr(skb, dataoff, dptr, datalen, matchoff, matchlen,
 117                               &addr, port))
 118                         return NF_DROP;
 119                 request = 1;
 120         } else
 121                 request = 0;
 122
 123         /* Translate topmost Via header and parameters */
 124         if (ct_sip_parse_header_uri(ct, *dptr, NULL, *datalen,
 125                                     SIP_HDR_VIA_UDP, NULL, &matchoff, &matchlen,
 126                                     &addr, &port) > 0) {
 127                 unsigned int matchend, poff, plen, buflen, n;
 128                 char buffer[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
 129
 130                 /* We're only interested in headers related to this
 131                  * connection */
 132                 if (request) {
 133                         if (addr.ip != ct->tuplehash[dir].tuple.src.u3.ip ||
 134                             port != ct->tuplehash[dir].tuple.src.u.udp.port)
 135                                 goto next;
 136                 } else {
 137                         if (addr.ip != ct->tuplehash[dir].tuple.dst.u3.ip ||
 138                             port != ct->tuplehash[dir].tuple.dst.u.udp.port)
 139                                 goto next;
 140                 }
 141
 142                 if (!map_addr(skb, dataoff, dptr, datalen, matchoff, matchlen,
 143                               &addr, port))
 144                         return NF_DROP;
 145
 146                 matchend = matchoff + matchlen;
 147
 148                 /* The maddr= parameter (RFC 2361) specifies where to send
 149                  * the reply. */
 150                 if (ct_sip_parse_address_param(ct, *dptr, matchend, *datalen,
 151                                                "maddr=", &poff, &plen,
 152                                                &addr) > 0 &&
 153                     addr.ip == ct->tuplehash[dir].tuple.src.u3.ip &&
 154                     addr.ip != ct->tuplehash[!dir].tuple.dst.u3.ip) {
 155                         buflen = sprintf(buffer, "%pI4",
 156                                         &ct->tuplehash[!dir].tuple.dst.u3.ip);
 157                         if (!mangle_packet(skb, dataoff, dptr, datalen,
 158                                            poff, plen, buffer, buflen))
 159                                 return NF_DROP;
 160                 }
 161
 162                 /* The received= parameter (RFC 2361) contains the address
 163                  * from which the server received the request. */
 164                 if (ct_sip_parse_address_param(ct, *dptr, matchend, *datalen,
 165                                                "received=", &poff, &plen,
 166                                                &addr) > 0 &&
 167                     addr.ip == ct->tuplehash[dir].tuple.dst.u3.ip &&
 168                     addr.ip != ct->tuplehash[!dir].tuple.src.u3.ip) {
 169                         buflen = sprintf(buffer, "%pI4",
 170                                         &ct->tuplehash[!dir].tuple.src.u3.ip);
 171                         if (!mangle_packet(skb, dataoff, dptr, datalen,
 172                                            poff, plen, buffer, buflen))
 173                                 return NF_DROP;
 174                 }
 175
 176                 /* The rport= parameter (RFC 3581) contains the port number
 177                  * from which the server received the request. */
 178                 if (ct_sip_parse_numerical_param(ct, *dptr, matchend, *datalen,
 179                                                  "rport=", &poff, &plen,
 180                                                  &n) > 0 &&
 181                     htons(n) == ct->tuplehash[dir].tuple.dst.u.udp.port &&
 182                     htons(n) != ct->tuplehash[!dir].tuple.src.u.udp.port) {
 183                         __be16 p = ct->tuplehash[!dir].tuple.src.u.udp.port;
 184                         buflen = sprintf(buffer, "%u", ntohs(p));
 185                         if (!mangle_packet(skb, dataoff, dptr, datalen,
 186                                            poff, plen, buffer, buflen))
 187                                 return NF_DROP;
 188                 }
 189         }
 190
 191 next:
 192         /* Translate Contact headers */
 193         coff = 0;
 194         in_header = 0;
 195         while (ct_sip_parse_header_uri(ct, *dptr, &coff, *datalen,
 196                                        SIP_HDR_CONTACT, &in_header,
 197                                        &matchoff, &matchlen,
 198                                        &addr, &port) > 0) {
 199                 if (!map_addr(skb, dataoff, dptr, datalen, matchoff, matchlen,
 200                               &addr, port))
 201                         return NF_DROP;
 202         }
 203
 204         if (!map_sip_addr(skb, dataoff, dptr, datalen, SIP_HDR_FROM) ||
 205             !map_sip_addr(skb, dataoff, dptr, datalen, SIP_HDR_TO))
 206                 return NF_DROP;
 207         return NF_ACCEPT;
 208 }
 209
 210 /* Handles expected signalling connections and media streams */
 211 static void ip_nat_sip_expected(struct nf_conn *ct,
 212                                 struct nf_conntrack_expect *exp)
 213 {
 214         struct nf_nat_range range;
 215
 216         /* This must be a fresh one. */
 217         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
 218
 219         /* For DST manip, map port here to where it's expected. */
 220         range.flags = (IP_NAT_RANGE_MAP_IPS | IP_NAT_RANGE_PROTO_SPECIFIED);
 221         range.min = range.max = exp->saved_proto;
 222         range.min_ip = range.max_ip = exp->saved_ip;
 223         nf_nat_setup_info(ct, &range, IP_NAT_MANIP_DST);
 224
 225         /* Change src to where master sends to, but only if the connection
 226          * actually came from the same source. */
 227         if (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip ==
 228             ct->master->tuplehash[exp->dir].tuple.src.u3.ip) {
 229                 range.flags = IP_NAT_RANGE_MAP_IPS;
 230                 range.min_ip = range.max_ip
 231                         = ct->master->tuplehash[!exp->dir].tuple.dst.u3.ip;
 232                 nf_nat_setup_info(ct, &range, IP_NAT_MANIP_SRC);
 233         }
 234 }
 235
 236 static unsigned int ip_nat_sip_expect(struct sk_buff *skb, unsigned int dataoff,
 237                                       const char **dptr, unsigned int *datalen,
 238                                       struct nf_conntrack_expect *exp,
 239                                       unsigned int matchoff,
 240                                       unsigned int matchlen)
 241 {
 242         enum ip_conntrack_info ctinfo;
 243         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 244         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 245         __be32 newip;
 246         u_int16_t port;
 247         char buffer[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
 248         unsigned buflen;
 249
 250         /* Connection will come from reply */
 251         if (ct->tuplehash[dir].tuple.src.u3.ip == ct->tuplehash[!dir].tuple.dst.u3.ip)
 252                 newip = exp->tuple.dst.u3.ip;
 253         else
 254                 newip = ct->tuplehash[!dir].tuple.dst.u3.ip;
 255
 256         /* If the signalling port matches the connection's source port in the
 257          * original direction, try to use the destination port in the opposite
 258          * direction. */
 259         if (exp->tuple.dst.u.udp.port ==
 260             ct->tuplehash[dir].tuple.src.u.udp.port)
 261                 port = ntohs(ct->tuplehash[!dir].tuple.dst.u.udp.port);
 262         else
 263                 port = ntohs(exp->tuple.dst.u.udp.port);
 264
 265         exp->saved_ip = exp->tuple.dst.u3.ip;
 266         exp->tuple.dst.u3.ip = newip;
 267         exp->saved_proto.udp.port = exp->tuple.dst.u.udp.port;
 268         exp->dir = !dir;
 269         exp->expectfn = ip_nat_sip_expected;
 270
 271         for (; port != 0; port++) {
 272                 exp->tuple.dst.u.udp.port = htons(port);
 273                 if (nf_ct_expect_related(exp) == 0)
 274                         break;
 275         }
 276
 277         if (port == 0)
 278                 return NF_DROP;
 279
 280         if (exp->tuple.dst.u3.ip != exp->saved_ip ||
 281             exp->tuple.dst.u.udp.port != exp->saved_proto.udp.port) {
 282                 buflen = sprintf(buffer, "%pI4:%u", &newip, port);
 283                 if (!mangle_packet(skb, dataoff, dptr, datalen,
 284                                    matchoff, matchlen, buffer, buflen))
 285                         goto err;
 286         }
 287         return NF_ACCEPT;
 288
 289 err:
 290         nf_ct_unexpect_related(exp);
 291         return NF_DROP;
 292 }
 293
 294 static int mangle_content_len(struct sk_buff *skb, unsigned int dataoff,
 295                               const char **dptr, unsigned int *datalen)
 296 {
 297         enum ip_conntrack_info ctinfo;
 298         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 299         unsigned int matchoff, matchlen;
 300         char buffer[sizeof("65536")];
 301         int buflen, c_len;
 302
 303         /* Get actual SDP length */
 304         if (ct_sip_get_sdp_header(ct, *dptr, 0, *datalen,
 305                                   SDP_HDR_VERSION, SDP_HDR_UNSPEC,
 306                                   &matchoff, &matchlen) <= 0)
 307                 return 0;
 308         c_len = *datalen - matchoff + strlen("v=");
 309
 310         /* Now, update SDP length */
 311         if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_CONTENT_LENGTH,
 312                               &matchoff, &matchlen) <= 0)
 313                 return 0;
 314
 315         buflen = sprintf(buffer, "%u", c_len);
 316         return mangle_packet(skb, dataoff, dptr, datalen, matchoff, matchlen,
 317                              buffer, buflen);
 318 }
 319
 320 static int mangle_sdp_packet(struct sk_buff *skb, unsigned int dataoff,
 321                              const char **dptr, unsigned int *datalen,
 322                              unsigned int sdpoff,
 323                              enum sdp_header_types type,
 324                              enum sdp_header_types term,
 325                              char *buffer, int buflen)
 326 {
 327         enum ip_conntrack_info ctinfo;
 328         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 329         unsigned int matchlen, matchoff;
 330
 331         if (ct_sip_get_sdp_header(ct, *dptr, sdpoff, *datalen, type, term,
 332                                   &matchoff, &matchlen) <= 0)
 333                 return -ENOENT;
 334         return mangle_packet(skb, dataoff, dptr, datalen, matchoff, matchlen,
 335                              buffer, buflen) ? 0 : -EINVAL;
 336 }
 337
 338 static unsigned int ip_nat_sdp_addr(struct sk_buff *skb, unsigned int dataoff,
 339                                     const char **dptr, unsigned int *datalen,
 340                                     unsigned int sdpoff,
 341                                     enum sdp_header_types type,
 342                                     enum sdp_header_types term,
 343                                     const union nf_inet_addr *addr)
 344 {
 345         char buffer[sizeof("nnn.nnn.nnn.nnn")];
 346         unsigned int buflen;
 347
 348         buflen = sprintf(buffer, "%pI4", &addr->ip);
 349         if (mangle_sdp_packet(skb, dataoff, dptr, datalen, sdpoff, type, term,
 350                               buffer, buflen))
 351                 return 0;
 352
 353         return mangle_content_len(skb, dataoff, dptr, datalen);
 354 }
 355
 356 static unsigned int ip_nat_sdp_port(struct sk_buff *skb, unsigned int dataoff,
 357                                     const char **dptr, unsigned int *datalen,
 358                                     unsigned int matchoff,
 359                                     unsigned int matchlen,
 360                                     u_int16_t port)
 361 {
 362         char buffer[sizeof("nnnnn")];
 363         unsigned int buflen;
 364
 365         buflen = sprintf(buffer, "%u", port);
 366         if (!mangle_packet(skb, dataoff, dptr, datalen, matchoff, matchlen,
 367                            buffer, buflen))
 368                 return 0;
 369
 370         return mangle_content_len(skb, dataoff, dptr, datalen);
 371 }
 372
 373 static unsigned int ip_nat_sdp_session(struct sk_buff *skb, unsigned int dataoff,
 374                                        const char **dptr, unsigned int *datalen,
 375                                        unsigned int sdpoff,
 376                                        const union nf_inet_addr *addr)
 377 {
 378         char buffer[sizeof("nnn.nnn.nnn.nnn")];
 379         unsigned int buflen;
 380
 381         /* Mangle session description owner and contact addresses */
 382         buflen = sprintf(buffer, "%pI4", &addr->ip);
 383         if (mangle_sdp_packet(skb, dataoff, dptr, datalen, sdpoff,
 384                                SDP_HDR_OWNER_IP4, SDP_HDR_MEDIA,
 385                                buffer, buflen))
 386                 return 0;
 387
 388         switch (mangle_sdp_packet(skb, dataoff, dptr, datalen, sdpoff,
 389                                   SDP_HDR_CONNECTION_IP4, SDP_HDR_MEDIA,
 390                                   buffer, buflen)) {
 391         case 0:
 392         /*
 393          * RFC 2327:
 394          *
 395          * Session description
 396          *
 397          * c=* (connection information - not required if included in all media)
 398          */
 399         case -ENOENT:
 400                 break;
 401         default:
 402                 return 0;
 403         }
 404
 405         return mangle_content_len(skb, dataoff, dptr, datalen);
 406 }
 407
 408 /* So, this packet has hit the connection tracking matching code.
 409    Mangle it, and change the expectation to match the new version. */
 410 static unsigned int ip_nat_sdp_media(struct sk_buff *skb, unsigned int dataoff,
 411                                      const char **dptr, unsigned int *datalen,
 412                                      struct nf_conntrack_expect *rtp_exp,
 413                                      struct nf_conntrack_expect *rtcp_exp,
 414                                      unsigned int mediaoff,
 415                                      unsigned int medialen,
 416                                      union nf_inet_addr *rtp_addr)
 417 {
 418         enum ip_conntrack_info ctinfo;
 419         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 420         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 421         u_int16_t port;
 422
 423         /* Connection will come from reply */
 424         if (ct->tuplehash[dir].tuple.src.u3.ip ==
 425             ct->tuplehash[!dir].tuple.dst.u3.ip)
 426                 rtp_addr->ip = rtp_exp->tuple.dst.u3.ip;
 427         else
 428                 rtp_addr->ip = ct->tuplehash[!dir].tuple.dst.u3.ip;
 429
 430         rtp_exp->saved_ip = rtp_exp->tuple.dst.u3.ip;
 431         rtp_exp->tuple.dst.u3.ip = rtp_addr->ip;
 432         rtp_exp->saved_proto.udp.port = rtp_exp->tuple.dst.u.udp.port;
 433         rtp_exp->dir = !dir;
 434         rtp_exp->expectfn = ip_nat_sip_expected;
 435
 436         rtcp_exp->saved_ip = rtcp_exp->tuple.dst.u3.ip;
 437         rtcp_exp->tuple.dst.u3.ip = rtp_addr->ip;
 438         rtcp_exp->saved_proto.udp.port = rtcp_exp->tuple.dst.u.udp.port;
 439         rtcp_exp->dir = !dir;
 440         rtcp_exp->expectfn = ip_nat_sip_expected;
 441
 442         /* Try to get same pair of ports: if not, try to change them. */
 443         for (port = ntohs(rtp_exp->tuple.dst.u.udp.port);
 444              port != 0; port += 2) {
 445                 rtp_exp->tuple.dst.u.udp.port = htons(port);
 446                 if (nf_ct_expect_related(rtp_exp) != 0)
 447                         continue;
 448                 rtcp_exp->tuple.dst.u.udp.port = htons(port + 1);
 449                 if (nf_ct_expect_related(rtcp_exp) == 0)
 450                         break;
 451                 nf_ct_unexpect_related(rtp_exp);
 452         }
 453
 454         if (port == 0)
 455                 goto err1;
 456
 457         /* Update media port. */
 458         if (rtp_exp->tuple.dst.u.udp.port != rtp_exp->saved_proto.udp.port &&
 459             !ip_nat_sdp_port(skb, dataoff, dptr, datalen,
 460                              mediaoff, medialen, port))
 461                 goto err2;
 462
 463         return NF_ACCEPT;
 464
 465 err2:
 466         nf_ct_unexpect_related(rtp_exp);
 467         nf_ct_unexpect_related(rtcp_exp);
 468 err1:
 469         return NF_DROP;
 470 }
 471
 472 static void __exit nf_nat_sip_fini(void)
 473 {
 474         rcu_assign_pointer(nf_nat_sip_hook, NULL);
 475         rcu_assign_pointer(nf_nat_sip_expect_hook, NULL);
 476         rcu_assign_pointer(nf_nat_sdp_addr_hook, NULL);
 477         rcu_assign_pointer(nf_nat_sdp_port_hook, NULL);
 478         rcu_assign_pointer(nf_nat_sdp_session_hook, NULL);
 479         rcu_assign_pointer(nf_nat_sdp_media_hook, NULL);
 480         synchronize_rcu();
 481 }
 482
 483 static int __init nf_nat_sip_init(void)
 484 {
 485         BUG_ON(nf_nat_sip_hook != NULL);
 486         BUG_ON(nf_nat_sip_expect_hook != NULL);
 487         BUG_ON(nf_nat_sdp_addr_hook != NULL);
 488         BUG_ON(nf_nat_sdp_port_hook != NULL);
 489         BUG_ON(nf_nat_sdp_session_hook != NULL);
 490         BUG_ON(nf_nat_sdp_media_hook != NULL);
 491         rcu_assign_pointer(nf_nat_sip_hook, ip_nat_sip);
 492         rcu_assign_pointer(nf_nat_sip_expect_hook, ip_nat_sip_expect);
 493         rcu_assign_pointer(nf_nat_sdp_addr_hook, ip_nat_sdp_addr);
 494         rcu_assign_pointer(nf_nat_sdp_port_hook, ip_nat_sdp_port);
 495         rcu_assign_pointer(nf_nat_sdp_session_hook, ip_nat_sdp_session);
 496         rcu_assign_pointer(nf_nat_sdp_media_hook, ip_nat_sdp_media);
 497         return 0;
 498 }
 499
 500 module_init(nf_nat_sip_init);
 501 module_exit(nf_nat_sip_fini);