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   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  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  */
  10
  11 #include <linux/module.h>
  12 #include <linux/skbuff.h>
  13 #include <linux/ip.h>
  14 #include <net/ip.h>
  15 #include <linux/udp.h>
  16
  17 #include <net/netfilter/nf_nat.h>
  18 #include <net/netfilter/nf_nat_helper.h>
  19 #include <net/netfilter/nf_nat_rule.h>
  20 #include <net/netfilter/nf_conntrack_helper.h>
  21 #include <net/netfilter/nf_conntrack_expect.h>
  22 #include <linux/netfilter/nf_conntrack_sip.h>
  23
  24 MODULE_LICENSE("GPL");
  25 MODULE_AUTHOR("Christian Hentschel <chentschel@arnet.com.ar>");
  26 MODULE_DESCRIPTION("SIP NAT helper");
  27 MODULE_ALIAS("ip_nat_sip");
  28
  29 struct addr_map {
  30         struct {
  31                 char            src[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
  32                 char            dst[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
  33                 unsigned int    srclen, srciplen;
  34                 unsigned int    dstlen, dstiplen;
  35         } addr[IP_CT_DIR_MAX];
  36 };
  37
  38 static void addr_map_init(struct nf_conn *ct, struct addr_map *map)
  39 {
  40         struct nf_conntrack_tuple *t;
  41         enum ip_conntrack_dir dir;
  42         unsigned int n;
  43
  44         for (dir = 0; dir < IP_CT_DIR_MAX; dir++) {
  45                 t = &ct->tuplehash[dir].tuple;
  46
  47                 n = sprintf(map->addr[dir].src, "%u.%u.%u.%u",
  48                             NIPQUAD(t->src.u3.ip));
  49                 map->addr[dir].srciplen = n;
  50                 n += sprintf(map->addr[dir].src + n, ":%u",
  51                              ntohs(t->src.u.udp.port));
  52                 map->addr[dir].srclen = n;
  53
  54                 n = sprintf(map->addr[dir].dst, "%u.%u.%u.%u",
  55                             NIPQUAD(t->dst.u3.ip));
  56                 map->addr[dir].dstiplen = n;
  57                 n += sprintf(map->addr[dir].dst + n, ":%u",
  58                              ntohs(t->dst.u.udp.port));
  59                 map->addr[dir].dstlen = n;
  60         }
  61 }
  62
  63 static int map_sip_addr(struct sk_buff *skb, enum ip_conntrack_info ctinfo,
  64                         struct nf_conn *ct, const char **dptr, size_t dlen,
  65                         enum sip_header_pos pos, struct addr_map *map)
  66 {
  67         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
  68         unsigned int matchlen, matchoff, addrlen;
  69         char *addr;
  70
  71         if (ct_sip_get_info(ct, *dptr, dlen, &matchoff, &matchlen, pos) <= 0)
  72                 return 1;
  73
  74         if ((matchlen == map->addr[dir].srciplen ||
  75              matchlen == map->addr[dir].srclen) &&
  76             memcmp(*dptr + matchoff, map->addr[dir].src, matchlen) == 0) {
  77                 addr    = map->addr[!dir].dst;
  78                 addrlen = map->addr[!dir].dstlen;
  79         } else if ((matchlen == map->addr[dir].dstiplen ||
  80                     matchlen == map->addr[dir].dstlen) &&
  81                    memcmp(*dptr + matchoff, map->addr[dir].dst, matchlen) == 0) {
  82                 addr    = map->addr[!dir].src;
  83                 addrlen = map->addr[!dir].srclen;
  84         } else
  85                 return 1;
  86
  87         if (!nf_nat_mangle_udp_packet(skb, ct, ctinfo,
  88                                       matchoff, matchlen, addr, addrlen))
  89                 return 0;
  90         *dptr = skb->data + ip_hdrlen(skb) + sizeof(struct udphdr);
  91         return 1;
  92
  93 }
  94
  95 static unsigned int ip_nat_sip(struct sk_buff *skb,
  96                                enum ip_conntrack_info ctinfo,
  97                                struct nf_conn *ct,
  98                                const char **dptr)
  99 {
 100         enum sip_header_pos pos;
 101         struct addr_map map;
 102         int dataoff, datalen;
 103
 104         dataoff = ip_hdrlen(skb) + sizeof(struct udphdr);
 105         datalen = skb->len - dataoff;
 106         if (datalen < sizeof("SIP/2.0") - 1)
 107                 return NF_ACCEPT;
 108
 109         addr_map_init(ct, &map);
 110
 111         /* Basic rules: requests and responses. */
 112         if (strncmp(*dptr, "SIP/2.0", sizeof("SIP/2.0") - 1) != 0) {
 113                 /* 10.2: Constructing the REGISTER Request:
 114                  *
 115                  * The "userinfo" and "@" components of the SIP URI MUST NOT
 116                  * be present.
 117                  */
 118                 if (datalen >= sizeof("REGISTER") - 1 &&
 119                     strncmp(*dptr, "REGISTER", sizeof("REGISTER") - 1) == 0)
 120                         pos = POS_REG_REQ_URI;
 121                 else
 122                         pos = POS_REQ_URI;
 123
 124                 if (!map_sip_addr(skb, ctinfo, ct, dptr, datalen, pos, &map))
 125                         return NF_DROP;
 126         }
 127
 128         if (!map_sip_addr(skb, ctinfo, ct, dptr, datalen, POS_FROM, &map) ||
 129             !map_sip_addr(skb, ctinfo, ct, dptr, datalen, POS_TO, &map) ||
 130             !map_sip_addr(skb, ctinfo, ct, dptr, datalen, POS_VIA, &map) ||
 131             !map_sip_addr(skb, ctinfo, ct, dptr, datalen, POS_CONTACT, &map))
 132                 return NF_DROP;
 133         return NF_ACCEPT;
 134 }
 135
 136 static unsigned int mangle_sip_packet(struct sk_buff *skb,
 137                                       enum ip_conntrack_info ctinfo,
 138                                       struct nf_conn *ct,
 139                                       const char **dptr, size_t dlen,
 140                                       char *buffer, int bufflen,
 141                                       enum sip_header_pos pos)
 142 {
 143         unsigned int matchlen, matchoff;
 144
 145         if (ct_sip_get_info(ct, *dptr, dlen, &matchoff, &matchlen, pos) <= 0)
 146                 return 0;
 147
 148         if (!nf_nat_mangle_udp_packet(skb, ct, ctinfo,
 149                                       matchoff, matchlen, buffer, bufflen))
 150                 return 0;
 151
 152         /* We need to reload this. Thanks Patrick. */
 153         *dptr = skb->data + ip_hdrlen(skb) + sizeof(struct udphdr);
 154         return 1;
 155 }
 156
 157 static int mangle_content_len(struct sk_buff *skb,
 158                               enum ip_conntrack_info ctinfo,
 159                               struct nf_conn *ct,
 160                               const char *dptr)
 161 {
 162         unsigned int dataoff, matchoff, matchlen;
 163         char buffer[sizeof("65536")];
 164         int bufflen;
 165
 166         dataoff = ip_hdrlen(skb) + sizeof(struct udphdr);
 167
 168         /* Get actual SDP length */
 169         if (ct_sip_get_info(ct, dptr, skb->len - dataoff, &matchoff,
 170                             &matchlen, POS_SDP_HEADER) > 0) {
 171
 172                 /* since ct_sip_get_info() give us a pointer passing 'v='
 173                    we need to add 2 bytes in this count. */
 174                 int c_len = skb->len - dataoff - matchoff + 2;
 175
 176                 /* Now, update SDP length */
 177                 if (ct_sip_get_info(ct, dptr, skb->len - dataoff, &matchoff,
 178                                     &matchlen, POS_CONTENT) > 0) {
 179
 180                         bufflen = sprintf(buffer, "%u", c_len);
 181                         return nf_nat_mangle_udp_packet(skb, ct, ctinfo,
 182                                                         matchoff, matchlen,
 183                                                         buffer, bufflen);
 184                 }
 185         }
 186         return 0;
 187 }
 188
 189 static unsigned int mangle_sdp(struct sk_buff *skb,
 190                                enum ip_conntrack_info ctinfo,
 191                                struct nf_conn *ct,
 192                                __be32 newip, u_int16_t port,
 193                                const char *dptr)
 194 {
 195         char buffer[sizeof("nnn.nnn.nnn.nnn")];
 196         unsigned int dataoff, bufflen;
 197
 198         dataoff = ip_hdrlen(skb) + sizeof(struct udphdr);
 199
 200         /* Mangle owner and contact info. */
 201         bufflen = sprintf(buffer, "%u.%u.%u.%u", NIPQUAD(newip));
 202         if (!mangle_sip_packet(skb, ctinfo, ct, &dptr, skb->len - dataoff,
 203                                buffer, bufflen, POS_OWNER_IP4))
 204                 return 0;
 205
 206         if (!mangle_sip_packet(skb, ctinfo, ct, &dptr, skb->len - dataoff,
 207                                buffer, bufflen, POS_CONNECTION_IP4))
 208                 return 0;
 209
 210         /* Mangle media port. */
 211         bufflen = sprintf(buffer, "%u", port);
 212         if (!mangle_sip_packet(skb, ctinfo, ct, &dptr, skb->len - dataoff,
 213                                buffer, bufflen, POS_MEDIA))
 214                 return 0;
 215
 216         return mangle_content_len(skb, ctinfo, ct, dptr);
 217 }
 218
 219 static void ip_nat_sdp_expect(struct nf_conn *ct,
 220                               struct nf_conntrack_expect *exp)
 221 {
 222         struct nf_nat_range range;
 223
 224         /* This must be a fresh one. */
 225         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
 226
 227         /* Change src to where master sends to */
 228         range.flags = IP_NAT_RANGE_MAP_IPS;
 229         range.min_ip = range.max_ip
 230                 = ct->master->tuplehash[!exp->dir].tuple.dst.u3.ip;
 231         /* hook doesn't matter, but it has to do source manip */
 232         nf_nat_setup_info(ct, &range, NF_INET_POST_ROUTING);
 233
 234         /* For DST manip, map port here to where it's expected. */
 235         range.flags = (IP_NAT_RANGE_MAP_IPS | IP_NAT_RANGE_PROTO_SPECIFIED);
 236         range.min = range.max = exp->saved_proto;
 237         range.min_ip = range.max_ip = exp->saved_ip;
 238         /* hook doesn't matter, but it has to do destination manip */
 239         nf_nat_setup_info(ct, &range, NF_INET_PRE_ROUTING);
 240 }
 241
 242 /* So, this packet has hit the connection tracking matching code.
 243    Mangle it, and change the expectation to match the new version. */
 244 static unsigned int ip_nat_sdp(struct sk_buff *skb,
 245                                enum ip_conntrack_info ctinfo,
 246                                struct nf_conntrack_expect *exp,
 247                                const char *dptr)
 248 {
 249         struct nf_conn *ct = exp->master;
 250         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 251         __be32 newip;
 252         u_int16_t port;
 253
 254         /* Connection will come from reply */
 255         if (ct->tuplehash[dir].tuple.src.u3.ip ==
 256             ct->tuplehash[!dir].tuple.dst.u3.ip)
 257                 newip = exp->tuple.dst.u3.ip;
 258         else
 259                 newip = ct->tuplehash[!dir].tuple.dst.u3.ip;
 260
 261         exp->saved_ip = exp->tuple.dst.u3.ip;
 262         exp->tuple.dst.u3.ip = newip;
 263         exp->saved_proto.udp.port = exp->tuple.dst.u.udp.port;
 264         exp->dir = !dir;
 265
 266         /* When you see the packet, we need to NAT it the same as the
 267            this one. */
 268         exp->expectfn = ip_nat_sdp_expect;
 269
 270         /* Try to get same port: if not, try to change it. */
 271         for (port = ntohs(exp->saved_proto.udp.port); 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 (!mangle_sdp(skb, ctinfo, ct, newip, port, dptr)) {
 281                 nf_ct_unexpect_related(exp);
 282                 return NF_DROP;
 283         }
 284         return NF_ACCEPT;
 285 }
 286
 287 static void __exit nf_nat_sip_fini(void)
 288 {
 289         rcu_assign_pointer(nf_nat_sip_hook, NULL);
 290         rcu_assign_pointer(nf_nat_sdp_hook, NULL);
 291         synchronize_rcu();
 292 }
 293
 294 static int __init nf_nat_sip_init(void)
 295 {
 296         BUG_ON(nf_nat_sip_hook != NULL);
 297         BUG_ON(nf_nat_sdp_hook != NULL);
 298         rcu_assign_pointer(nf_nat_sip_hook, ip_nat_sip);
 299         rcu_assign_pointer(nf_nat_sdp_hook, ip_nat_sdp);
 300         return 0;
 301 }
 302
 303 module_init(nf_nat_sip_init);
 304 module_exit(nf_nat_sip_fini);