net/netfilter/nf_nat_sip.c

   1 /* SIP extension for 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, 2011, 2012 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/inet.h>
  16 #include <linux/udp.h>
  17 #include <linux/tcp.h>
  18
  19 #include <net/netfilter/nf_nat.h>
  20 #include <net/netfilter/nf_nat_helper.h>
  21 #include <net/netfilter/nf_conntrack_helper.h>
  22 #include <net/netfilter/nf_conntrack_expect.h>
  23 #include <linux/netfilter/nf_conntrack_sip.h>
  24
  25 MODULE_LICENSE("GPL");
  26 MODULE_AUTHOR("Christian Hentschel <chentschel@arnet.com.ar>");
  27 MODULE_DESCRIPTION("SIP NAT helper");
  28 MODULE_ALIAS("ip_nat_sip");
  29
  30
  31 static unsigned int mangle_packet(struct sk_buff *skb, unsigned int protoff,
  32                                   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         struct tcphdr *th;
  40         unsigned int baseoff;
  41
  42         if (nf_ct_protonum(ct) == IPPROTO_TCP) {
  43                 th = (struct tcphdr *)(skb->data + protoff);
  44                 baseoff = protoff + th->doff * 4;
  45                 matchoff += dataoff - baseoff;
  46
  47                 if (!__nf_nat_mangle_tcp_packet(skb, ct, ctinfo,
  48                                                 protoff, matchoff, matchlen,
  49                                                 buffer, buflen, false))
  50                         return 0;
  51         } else {
  52                 baseoff = protoff + sizeof(struct udphdr);
  53                 matchoff += dataoff - baseoff;
  54
  55                 if (!nf_nat_mangle_udp_packet(skb, ct, ctinfo,
  56                                               protoff, matchoff, matchlen,
  57                                               buffer, buflen))
  58                         return 0;
  59         }
  60
  61         /* Reload data pointer and adjust datalen value */
  62         *dptr = skb->data + dataoff;
  63         *datalen += buflen - matchlen;
  64         return 1;
  65 }
  66
  67 static int sip_sprintf_addr(const struct nf_conn *ct, char *buffer,
  68                             const union nf_inet_addr *addr, bool delim)
  69 {
  70         if (nf_ct_l3num(ct) == NFPROTO_IPV4)
  71                 return sprintf(buffer, "%pI4", &addr->ip);
  72         else {
  73                 if (delim)
  74                         return sprintf(buffer, "[%pI6c]", &addr->ip6);
  75                 else
  76                         return sprintf(buffer, "%pI6c", &addr->ip6);
  77         }
  78 }
  79
  80 static int sip_sprintf_addr_port(const struct nf_conn *ct, char *buffer,
  81                                  const union nf_inet_addr *addr, u16 port)
  82 {
  83         if (nf_ct_l3num(ct) == NFPROTO_IPV4)
  84                 return sprintf(buffer, "%pI4:%u", &addr->ip, port);
  85         else
  86                 return sprintf(buffer, "[%pI6c]:%u", &addr->ip6, port);
  87 }
  88
  89 static int map_addr(struct sk_buff *skb, unsigned int protoff,
  90                     unsigned int dataoff,
  91                     const char **dptr, unsigned int *datalen,
  92                     unsigned int matchoff, unsigned int matchlen,
  93                     union nf_inet_addr *addr, __be16 port)
  94 {
  95         enum ip_conntrack_info ctinfo;
  96         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
  97         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
  98         char buffer[INET6_ADDRSTRLEN + sizeof("[]:nnnnn")];
  99         unsigned int buflen;
 100         union nf_inet_addr newaddr;
 101         __be16 newport;
 102
 103         if (nf_inet_addr_cmp(&ct->tuplehash[dir].tuple.src.u3, addr) &&
 104             ct->tuplehash[dir].tuple.src.u.udp.port == port) {
 105                 newaddr = ct->tuplehash[!dir].tuple.dst.u3;
 106                 newport = ct->tuplehash[!dir].tuple.dst.u.udp.port;
 107         } else if (nf_inet_addr_cmp(&ct->tuplehash[dir].tuple.dst.u3, addr) &&
 108                    ct->tuplehash[dir].tuple.dst.u.udp.port == port) {
 109                 newaddr = ct->tuplehash[!dir].tuple.src.u3;
 110                 newport = ct->tuplehash[!dir].tuple.src.u.udp.port;
 111         } else
 112                 return 1;
 113
 114         if (nf_inet_addr_cmp(&newaddr, addr) && newport == port)
 115                 return 1;
 116
 117         buflen = sip_sprintf_addr_port(ct, buffer, &newaddr, ntohs(newport));
 118         return mangle_packet(skb, protoff, dataoff, dptr, datalen,
 119                              matchoff, matchlen, buffer, buflen);
 120 }
 121
 122 static int map_sip_addr(struct sk_buff *skb, unsigned int protoff,
 123                         unsigned int dataoff,
 124                         const char **dptr, unsigned int *datalen,
 125                         enum sip_header_types type)
 126 {
 127         enum ip_conntrack_info ctinfo;
 128         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 129         unsigned int matchlen, matchoff;
 130         union nf_inet_addr addr;
 131         __be16 port;
 132
 133         if (ct_sip_parse_header_uri(ct, *dptr, NULL, *datalen, type, NULL,
 134                                     &matchoff, &matchlen, &addr, &port) <= 0)
 135                 return 1;
 136         return map_addr(skb, protoff, dataoff, dptr, datalen,
 137                         matchoff, matchlen, &addr, port);
 138 }
 139
 140 static unsigned int nf_nat_sip(struct sk_buff *skb, unsigned int protoff,
 141                                unsigned int dataoff,
 142                                const char **dptr, unsigned int *datalen)
 143 {
 144         enum ip_conntrack_info ctinfo;
 145         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 146         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 147         unsigned int coff, matchoff, matchlen;
 148         enum sip_header_types hdr;
 149         union nf_inet_addr addr;
 150         __be16 port;
 151         int request, in_header;
 152
 153         /* Basic rules: requests and responses. */
 154         if (strnicmp(*dptr, "SIP/2.0", strlen("SIP/2.0")) != 0) {
 155                 if (ct_sip_parse_request(ct, *dptr, *datalen,
 156                                          &matchoff, &matchlen,
 157                                          &addr, &port) > 0 &&
 158                     !map_addr(skb, protoff, dataoff, dptr, datalen,
 159                               matchoff, matchlen, &addr, port))
 160                         return NF_DROP;
 161                 request = 1;
 162         } else
 163                 request = 0;
 164
 165         if (nf_ct_protonum(ct) == IPPROTO_TCP)
 166                 hdr = SIP_HDR_VIA_TCP;
 167         else
 168                 hdr = SIP_HDR_VIA_UDP;
 169
 170         /* Translate topmost Via header and parameters */
 171         if (ct_sip_parse_header_uri(ct, *dptr, NULL, *datalen,
 172                                     hdr, NULL, &matchoff, &matchlen,
 173                                     &addr, &port) > 0) {
 174                 unsigned int olen, matchend, poff, plen, buflen, n;
 175                 char buffer[INET6_ADDRSTRLEN + sizeof("[]:nnnnn")];
 176
 177                 /* We're only interested in headers related to this
 178                  * connection */
 179                 if (request) {
 180                         if (!nf_inet_addr_cmp(&addr,
 181                                         &ct->tuplehash[dir].tuple.src.u3) ||
 182                             port != ct->tuplehash[dir].tuple.src.u.udp.port)
 183                                 goto next;
 184                 } else {
 185                         if (!nf_inet_addr_cmp(&addr,
 186                                         &ct->tuplehash[dir].tuple.dst.u3) ||
 187                             port != ct->tuplehash[dir].tuple.dst.u.udp.port)
 188                                 goto next;
 189                 }
 190
 191                 olen = *datalen;
 192                 if (!map_addr(skb, protoff, dataoff, dptr, datalen,
 193                               matchoff, matchlen, &addr, port))
 194                         return NF_DROP;
 195
 196                 matchend = matchoff + matchlen + *datalen - olen;
 197
 198                 /* The maddr= parameter (RFC 2361) specifies where to send
 199                  * the reply. */
 200                 if (ct_sip_parse_address_param(ct, *dptr, matchend, *datalen,
 201                                                "maddr=", &poff, &plen,
 202                                                &addr, true) > 0 &&
 203                     nf_inet_addr_cmp(&addr, &ct->tuplehash[dir].tuple.src.u3) &&
 204                     !nf_inet_addr_cmp(&addr, &ct->tuplehash[!dir].tuple.dst.u3)) {
 205                         buflen = sip_sprintf_addr(ct, buffer,
 206                                         &ct->tuplehash[!dir].tuple.dst.u3,
 207                                         true);
 208                         if (!mangle_packet(skb, protoff, dataoff, dptr, datalen,
 209                                            poff, plen, buffer, buflen))
 210                                 return NF_DROP;
 211                 }
 212
 213                 /* The received= parameter (RFC 2361) contains the address
 214                  * from which the server received the request. */
 215                 if (ct_sip_parse_address_param(ct, *dptr, matchend, *datalen,
 216                                                "received=", &poff, &plen,
 217                                                &addr, false) > 0 &&
 218                     nf_inet_addr_cmp(&addr, &ct->tuplehash[dir].tuple.dst.u3) &&
 219                     !nf_inet_addr_cmp(&addr, &ct->tuplehash[!dir].tuple.src.u3)) {
 220                         buflen = sip_sprintf_addr(ct, buffer,
 221                                         &ct->tuplehash[!dir].tuple.src.u3,
 222                                         false);
 223                         if (!mangle_packet(skb, protoff, dataoff, dptr, datalen,
 224                                            poff, plen, buffer, buflen))
 225                                 return NF_DROP;
 226                 }
 227
 228                 /* The rport= parameter (RFC 3581) contains the port number
 229                  * from which the server received the request. */
 230                 if (ct_sip_parse_numerical_param(ct, *dptr, matchend, *datalen,
 231                                                  "rport=", &poff, &plen,
 232                                                  &n) > 0 &&
 233                     htons(n) == ct->tuplehash[dir].tuple.dst.u.udp.port &&
 234                     htons(n) != ct->tuplehash[!dir].tuple.src.u.udp.port) {
 235                         __be16 p = ct->tuplehash[!dir].tuple.src.u.udp.port;
 236                         buflen = sprintf(buffer, "%u", ntohs(p));
 237                         if (!mangle_packet(skb, protoff, dataoff, dptr, datalen,
 238                                            poff, plen, buffer, buflen))
 239                                 return NF_DROP;
 240                 }
 241         }
 242
 243 next:
 244         /* Translate Contact headers */
 245         coff = 0;
 246         in_header = 0;
 247         while (ct_sip_parse_header_uri(ct, *dptr, &coff, *datalen,
 248                                        SIP_HDR_CONTACT, &in_header,
 249                                        &matchoff, &matchlen,
 250                                        &addr, &port) > 0) {
 251                 if (!map_addr(skb, protoff, dataoff, dptr, datalen,
 252                               matchoff, matchlen,
 253                               &addr, port))
 254                         return NF_DROP;
 255         }
 256
 257         if (!map_sip_addr(skb, protoff, dataoff, dptr, datalen, SIP_HDR_FROM) ||
 258             !map_sip_addr(skb, protoff, dataoff, dptr, datalen, SIP_HDR_TO))
 259                 return NF_DROP;
 260
 261         return NF_ACCEPT;
 262 }
 263
 264 static void nf_nat_sip_seq_adjust(struct sk_buff *skb, unsigned int protoff,
 265                                   s16 off)
 266 {
 267         enum ip_conntrack_info ctinfo;
 268         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 269         const struct tcphdr *th;
 270
 271         if (nf_ct_protonum(ct) != IPPROTO_TCP || off == 0)
 272                 return;
 273
 274         th = (struct tcphdr *)(skb->data + protoff);
 275         nf_nat_set_seq_adjust(ct, ctinfo, th->seq, off);
 276 }
 277
 278 /* Handles expected signalling connections and media streams */
 279 static void nf_nat_sip_expected(struct nf_conn *ct,
 280                                 struct nf_conntrack_expect *exp)
 281 {
 282         struct nf_nat_range range;
 283
 284         /* This must be a fresh one. */
 285         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
 286
 287         /* For DST manip, map port here to where it's expected. */
 288         range.flags = (NF_NAT_RANGE_MAP_IPS | NF_NAT_RANGE_PROTO_SPECIFIED);
 289         range.min_proto = range.max_proto = exp->saved_proto;
 290         range.min_addr = range.max_addr = exp->saved_addr;
 291         nf_nat_setup_info(ct, &range, NF_NAT_MANIP_DST);
 292
 293         /* Change src to where master sends to, but only if the connection
 294          * actually came from the same source. */
 295         if (nf_inet_addr_cmp(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3,
 296                              &ct->master->tuplehash[exp->dir].tuple.src.u3)) {
 297                 range.flags = NF_NAT_RANGE_MAP_IPS;
 298                 range.min_addr = range.max_addr
 299                         = ct->master->tuplehash[!exp->dir].tuple.dst.u3;
 300                 nf_nat_setup_info(ct, &range, NF_NAT_MANIP_SRC);
 301         }
 302 }
 303
 304 static unsigned int nf_nat_sip_expect(struct sk_buff *skb, unsigned int protoff,
 305                                       unsigned int dataoff,
 306                                       const char **dptr, unsigned int *datalen,
 307                                       struct nf_conntrack_expect *exp,
 308                                       unsigned int matchoff,
 309                                       unsigned int matchlen)
 310 {
 311         enum ip_conntrack_info ctinfo;
 312         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 313         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 314         union nf_inet_addr newaddr;
 315         u_int16_t port;
 316         char buffer[INET6_ADDRSTRLEN + sizeof("[]:nnnnn")];
 317         unsigned int buflen;
 318
 319         /* Connection will come from reply */
 320         if (nf_inet_addr_cmp(&ct->tuplehash[dir].tuple.src.u3,
 321                              &ct->tuplehash[!dir].tuple.dst.u3))
 322                 newaddr = exp->tuple.dst.u3;
 323         else
 324                 newaddr = ct->tuplehash[!dir].tuple.dst.u3;
 325
 326         /* If the signalling port matches the connection's source port in the
 327          * original direction, try to use the destination port in the opposite
 328          * direction. */
 329         if (exp->tuple.dst.u.udp.port ==
 330             ct->tuplehash[dir].tuple.src.u.udp.port)
 331                 port = ntohs(ct->tuplehash[!dir].tuple.dst.u.udp.port);
 332         else
 333                 port = ntohs(exp->tuple.dst.u.udp.port);
 334
 335         exp->saved_addr = exp->tuple.dst.u3;
 336         exp->tuple.dst.u3 = newaddr;
 337         exp->saved_proto.udp.port = exp->tuple.dst.u.udp.port;
 338         exp->dir = !dir;
 339         exp->expectfn = nf_nat_sip_expected;
 340
 341         for (; port != 0; port++) {
 342                 int ret;
 343
 344                 exp->tuple.dst.u.udp.port = htons(port);
 345                 ret = nf_ct_expect_related(exp);
 346                 if (ret == 0)
 347                         break;
 348                 else if (ret != -EBUSY) {
 349                         port = 0;
 350                         break;
 351                 }
 352         }
 353
 354         if (port == 0)
 355                 return NF_DROP;
 356
 357         if (!nf_inet_addr_cmp(&exp->tuple.dst.u3, &exp->saved_addr) ||
 358             exp->tuple.dst.u.udp.port != exp->saved_proto.udp.port) {
 359                 buflen = sip_sprintf_addr_port(ct, buffer, &newaddr, port);
 360                 if (!mangle_packet(skb, protoff, dataoff, dptr, datalen,
 361                                    matchoff, matchlen, buffer, buflen))
 362                         goto err;
 363         }
 364         return NF_ACCEPT;
 365
 366 err:
 367         nf_ct_unexpect_related(exp);
 368         return NF_DROP;
 369 }
 370
 371 static int mangle_content_len(struct sk_buff *skb, unsigned int protoff,
 372                               unsigned int dataoff,
 373                               const char **dptr, unsigned int *datalen)
 374 {
 375         enum ip_conntrack_info ctinfo;
 376         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 377         unsigned int matchoff, matchlen;
 378         char buffer[sizeof("65536")];
 379         int buflen, c_len;
 380
 381         /* Get actual SDP length */
 382         if (ct_sip_get_sdp_header(ct, *dptr, 0, *datalen,
 383                                   SDP_HDR_VERSION, SDP_HDR_UNSPEC,
 384                                   &matchoff, &matchlen) <= 0)
 385                 return 0;
 386         c_len = *datalen - matchoff + strlen("v=");
 387
 388         /* Now, update SDP length */
 389         if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_CONTENT_LENGTH,
 390                               &matchoff, &matchlen) <= 0)
 391                 return 0;
 392
 393         buflen = sprintf(buffer, "%u", c_len);
 394         return mangle_packet(skb, protoff, dataoff, dptr, datalen,
 395                              matchoff, matchlen, buffer, buflen);
 396 }
 397
 398 static int mangle_sdp_packet(struct sk_buff *skb, unsigned int protoff,
 399                              unsigned int dataoff,
 400                              const char **dptr, unsigned int *datalen,
 401                              unsigned int sdpoff,
 402                              enum sdp_header_types type,
 403                              enum sdp_header_types term,
 404                              char *buffer, int buflen)
 405 {
 406         enum ip_conntrack_info ctinfo;
 407         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 408         unsigned int matchlen, matchoff;
 409
 410         if (ct_sip_get_sdp_header(ct, *dptr, sdpoff, *datalen, type, term,
 411                                   &matchoff, &matchlen) <= 0)
 412                 return -ENOENT;
 413         return mangle_packet(skb, protoff, dataoff, dptr, datalen,
 414                              matchoff, matchlen, buffer, buflen) ? 0 : -EINVAL;
 415 }
 416
 417 static unsigned int nf_nat_sdp_addr(struct sk_buff *skb, unsigned int protoff,
 418                                     unsigned int dataoff,
 419                                     const char **dptr, unsigned int *datalen,
 420                                     unsigned int sdpoff,
 421                                     enum sdp_header_types type,
 422                                     enum sdp_header_types term,
 423                                     const union nf_inet_addr *addr)
 424 {
 425         enum ip_conntrack_info ctinfo;
 426         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 427         char buffer[INET6_ADDRSTRLEN];
 428         unsigned int buflen;
 429
 430         buflen = sip_sprintf_addr(ct, buffer, addr, false);
 431         if (mangle_sdp_packet(skb, protoff, dataoff, dptr, datalen,
 432                               sdpoff, type, term, buffer, buflen))
 433                 return 0;
 434
 435         return mangle_content_len(skb, protoff, dataoff, dptr, datalen);
 436 }
 437
 438 static unsigned int nf_nat_sdp_port(struct sk_buff *skb, unsigned int protoff,
 439                                     unsigned int dataoff,
 440                                     const char **dptr, unsigned int *datalen,
 441                                     unsigned int matchoff,
 442                                     unsigned int matchlen,
 443                                     u_int16_t port)
 444 {
 445         char buffer[sizeof("nnnnn")];
 446         unsigned int buflen;
 447
 448         buflen = sprintf(buffer, "%u", port);
 449         if (!mangle_packet(skb, protoff, dataoff, dptr, datalen,
 450                            matchoff, matchlen, buffer, buflen))
 451                 return 0;
 452
 453         return mangle_content_len(skb, protoff, dataoff, dptr, datalen);
 454 }
 455
 456 static unsigned int nf_nat_sdp_session(struct sk_buff *skb, unsigned int protoff,
 457                                        unsigned int dataoff,
 458                                        const char **dptr, unsigned int *datalen,
 459                                        unsigned int sdpoff,
 460                                        const union nf_inet_addr *addr)
 461 {
 462         enum ip_conntrack_info ctinfo;
 463         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 464         char buffer[INET6_ADDRSTRLEN];
 465         unsigned int buflen;
 466
 467         /* Mangle session description owner and contact addresses */
 468         buflen = sip_sprintf_addr(ct, buffer, addr, false);
 469         if (mangle_sdp_packet(skb, protoff, dataoff, dptr, datalen, sdpoff,
 470                               SDP_HDR_OWNER, SDP_HDR_MEDIA, buffer, buflen))
 471                 return 0;
 472
 473         switch (mangle_sdp_packet(skb, protoff, dataoff, dptr, datalen, sdpoff,
 474                                   SDP_HDR_CONNECTION, SDP_HDR_MEDIA,
 475                                   buffer, buflen)) {
 476         case 0:
 477         /*
 478          * RFC 2327:
 479          *
 480          * Session description
 481          *
 482          * c=* (connection information - not required if included in all media)
 483          */
 484         case -ENOENT:
 485                 break;
 486         default:
 487                 return 0;
 488         }
 489
 490         return mangle_content_len(skb, protoff, dataoff, dptr, datalen);
 491 }
 492
 493 /* So, this packet has hit the connection tracking matching code.
 494    Mangle it, and change the expectation to match the new version. */
 495 static unsigned int nf_nat_sdp_media(struct sk_buff *skb, unsigned int protoff,
 496                                      unsigned int dataoff,
 497                                      const char **dptr, unsigned int *datalen,
 498                                      struct nf_conntrack_expect *rtp_exp,
 499                                      struct nf_conntrack_expect *rtcp_exp,
 500                                      unsigned int mediaoff,
 501                                      unsigned int medialen,
 502                                      union nf_inet_addr *rtp_addr)
 503 {
 504         enum ip_conntrack_info ctinfo;
 505         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 506         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 507         u_int16_t port;
 508
 509         /* Connection will come from reply */
 510         if (nf_inet_addr_cmp(&ct->tuplehash[dir].tuple.src.u3,
 511                              &ct->tuplehash[!dir].tuple.dst.u3))
 512                 *rtp_addr = rtp_exp->tuple.dst.u3;
 513         else
 514                 *rtp_addr = ct->tuplehash[!dir].tuple.dst.u3;
 515
 516         rtp_exp->saved_addr = rtp_exp->tuple.dst.u3;
 517         rtp_exp->tuple.dst.u3 = *rtp_addr;
 518         rtp_exp->saved_proto.udp.port = rtp_exp->tuple.dst.u.udp.port;
 519         rtp_exp->dir = !dir;
 520         rtp_exp->expectfn = nf_nat_sip_expected;
 521
 522         rtcp_exp->saved_addr = rtcp_exp->tuple.dst.u3;
 523         rtcp_exp->tuple.dst.u3 = *rtp_addr;
 524         rtcp_exp->saved_proto.udp.port = rtcp_exp->tuple.dst.u.udp.port;
 525         rtcp_exp->dir = !dir;
 526         rtcp_exp->expectfn = nf_nat_sip_expected;
 527
 528         /* Try to get same pair of ports: if not, try to change them. */
 529         for (port = ntohs(rtp_exp->tuple.dst.u.udp.port);
 530              port != 0; port += 2) {
 531                 int ret;
 532
 533                 rtp_exp->tuple.dst.u.udp.port = htons(port);
 534                 ret = nf_ct_expect_related(rtp_exp);
 535                 if (ret == -EBUSY)
 536                         continue;
 537                 else if (ret < 0) {
 538                         port = 0;
 539                         break;
 540                 }
 541                 rtcp_exp->tuple.dst.u.udp.port = htons(port + 1);
 542                 ret = nf_ct_expect_related(rtcp_exp);
 543                 if (ret == 0)
 544                         break;
 545                 else if (ret == -EBUSY) {
 546                         nf_ct_unexpect_related(rtp_exp);
 547                         continue;
 548                 } else if (ret < 0) {
 549                         nf_ct_unexpect_related(rtp_exp);
 550                         port = 0;
 551                         break;
 552                 }
 553         }
 554
 555         if (port == 0)
 556                 goto err1;
 557
 558         /* Update media port. */
 559         if (rtp_exp->tuple.dst.u.udp.port != rtp_exp->saved_proto.udp.port &&
 560             !nf_nat_sdp_port(skb, protoff, dataoff, dptr, datalen,
 561                              mediaoff, medialen, port))
 562                 goto err2;
 563
 564         return NF_ACCEPT;
 565
 566 err2:
 567         nf_ct_unexpect_related(rtp_exp);
 568         nf_ct_unexpect_related(rtcp_exp);
 569 err1:
 570         return NF_DROP;
 571 }
 572
 573 static struct nf_ct_helper_expectfn sip_nat = {
 574         .name           = "sip",
 575         .expectfn       = nf_nat_sip_expected,
 576 };
 577
 578 static void __exit nf_nat_sip_fini(void)
 579 {
 580         RCU_INIT_POINTER(nf_nat_sip_hook, NULL);
 581         RCU_INIT_POINTER(nf_nat_sip_seq_adjust_hook, NULL);
 582         RCU_INIT_POINTER(nf_nat_sip_expect_hook, NULL);
 583         RCU_INIT_POINTER(nf_nat_sdp_addr_hook, NULL);
 584         RCU_INIT_POINTER(nf_nat_sdp_port_hook, NULL);
 585         RCU_INIT_POINTER(nf_nat_sdp_session_hook, NULL);
 586         RCU_INIT_POINTER(nf_nat_sdp_media_hook, NULL);
 587         nf_ct_helper_expectfn_unregister(&sip_nat);
 588         synchronize_rcu();
 589 }
 590
 591 static int __init nf_nat_sip_init(void)
 592 {
 593         BUG_ON(nf_nat_sip_hook != NULL);
 594         BUG_ON(nf_nat_sip_seq_adjust_hook != NULL);
 595         BUG_ON(nf_nat_sip_expect_hook != NULL);
 596         BUG_ON(nf_nat_sdp_addr_hook != NULL);
 597         BUG_ON(nf_nat_sdp_port_hook != NULL);
 598         BUG_ON(nf_nat_sdp_session_hook != NULL);
 599         BUG_ON(nf_nat_sdp_media_hook != NULL);
 600         RCU_INIT_POINTER(nf_nat_sip_hook, nf_nat_sip);
 601         RCU_INIT_POINTER(nf_nat_sip_seq_adjust_hook, nf_nat_sip_seq_adjust);
 602         RCU_INIT_POINTER(nf_nat_sip_expect_hook, nf_nat_sip_expect);
 603         RCU_INIT_POINTER(nf_nat_sdp_addr_hook, nf_nat_sdp_addr);
 604         RCU_INIT_POINTER(nf_nat_sdp_port_hook, nf_nat_sdp_port);
 605         RCU_INIT_POINTER(nf_nat_sdp_session_hook, nf_nat_sdp_session);
 606         RCU_INIT_POINTER(nf_nat_sdp_media_hook, nf_nat_sdp_media);
 607         nf_ct_helper_expectfn_register(&sip_nat);
 608         return 0;
 609 }
 610
 611 module_init(nf_nat_sip_init);
 612 module_exit(nf_nat_sip_fini);