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  *
   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 #if 0
  30 #define DEBUGP printk
  31 #else
  32 #define DEBUGP(format, args...)
  33 #endif
  34
  35 struct addr_map {
  36         struct {
  37                 char            src[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
  38                 char            dst[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
  39                 unsigned int    srclen, srciplen;
  40                 unsigned int    dstlen, dstiplen;
  41         } addr[IP_CT_DIR_MAX];
  42 };
  43
  44 static void addr_map_init(struct nf_conn *ct, struct addr_map *map)
  45 {
  46         struct nf_conntrack_tuple *t;
  47         enum ip_conntrack_dir dir;
  48         unsigned int n;
  49
  50         for (dir = 0; dir < IP_CT_DIR_MAX; dir++) {
  51                 t = &ct->tuplehash[dir].tuple;
  52
  53                 n = sprintf(map->addr[dir].src, "%u.%u.%u.%u",
  54                             NIPQUAD(t->src.u3.ip));
  55                 map->addr[dir].srciplen = n;
  56                 n += sprintf(map->addr[dir].src + n, ":%u",
  57                              ntohs(t->src.u.udp.port));
  58                 map->addr[dir].srclen = n;
  59
  60                 n = sprintf(map->addr[dir].dst, "%u.%u.%u.%u",
  61                             NIPQUAD(t->dst.u3.ip));
  62                 map->addr[dir].dstiplen = n;
  63                 n += sprintf(map->addr[dir].dst + n, ":%u",
  64                              ntohs(t->dst.u.udp.port));
  65                 map->addr[dir].dstlen = n;
  66         }
  67 }
  68
  69 static int map_sip_addr(struct sk_buff **pskb, enum ip_conntrack_info ctinfo,
  70                         struct nf_conn *ct, const char **dptr, size_t dlen,
  71                         enum sip_header_pos pos, struct addr_map *map)
  72 {
  73         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
  74         unsigned int matchlen, matchoff, addrlen;
  75         char *addr;
  76
  77         if (ct_sip_get_info(ct, *dptr, dlen, &matchoff, &matchlen, pos) <= 0)
  78                 return 1;
  79
  80         if ((matchlen == map->addr[dir].srciplen ||
  81              matchlen == map->addr[dir].srclen) &&
  82             memcmp(*dptr + matchoff, map->addr[dir].src, matchlen) == 0) {
  83                 addr    = map->addr[!dir].dst;
  84                 addrlen = map->addr[!dir].dstlen;
  85         } else if ((matchlen == map->addr[dir].dstiplen ||
  86                     matchlen == map->addr[dir].dstlen) &&
  87                    memcmp(*dptr + matchoff, map->addr[dir].dst, matchlen) == 0) {
  88                 addr    = map->addr[!dir].src;
  89                 addrlen = map->addr[!dir].srclen;
  90         } else
  91                 return 1;
  92
  93         if (!nf_nat_mangle_udp_packet(pskb, ct, ctinfo,
  94                                       matchoff, matchlen, addr, addrlen))
  95                 return 0;
  96         *dptr = (*pskb)->data + ip_hdrlen(*pskb) + sizeof(struct udphdr);
  97         return 1;
  98
  99 }
 100
 101 static unsigned int ip_nat_sip(struct sk_buff **pskb,
 102                                enum ip_conntrack_info ctinfo,
 103                                struct nf_conn *ct,
 104                                const char **dptr)
 105 {
 106         enum sip_header_pos pos;
 107         struct addr_map map;
 108         int dataoff, datalen;
 109
 110         dataoff = ip_hdrlen(*pskb) + sizeof(struct udphdr);
 111         datalen = (*pskb)->len - dataoff;
 112         if (datalen < sizeof("SIP/2.0") - 1)
 113                 return NF_DROP;
 114
 115         addr_map_init(ct, &map);
 116
 117         /* Basic rules: requests and responses. */
 118         if (strncmp(*dptr, "SIP/2.0", sizeof("SIP/2.0") - 1) != 0) {
 119                 /* 10.2: Constructing the REGISTER Request:
 120                  *
 121                  * The "userinfo" and "@" components of the SIP URI MUST NOT
 122                  * be present.
 123                  */
 124                 if (datalen >= sizeof("REGISTER") - 1 &&
 125                     strncmp(*dptr, "REGISTER", sizeof("REGISTER") - 1) == 0)
 126                         pos = POS_REG_REQ_URI;
 127                 else
 128                         pos = POS_REQ_URI;
 129
 130                 if (!map_sip_addr(pskb, ctinfo, ct, dptr, datalen, pos, &map))
 131                         return NF_DROP;
 132         }
 133
 134         if (!map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_FROM, &map) ||
 135             !map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_TO, &map) ||
 136             !map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_VIA, &map) ||
 137             !map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_CONTACT, &map))
 138                 return NF_DROP;
 139         return NF_ACCEPT;
 140 }
 141
 142 static unsigned int mangle_sip_packet(struct sk_buff **pskb,
 143                                       enum ip_conntrack_info ctinfo,
 144                                       struct nf_conn *ct,
 145                                       const char **dptr, size_t dlen,
 146                                       char *buffer, int bufflen,
 147                                       enum sip_header_pos pos)
 148 {
 149         unsigned int matchlen, matchoff;
 150
 151         if (ct_sip_get_info(ct, *dptr, dlen, &matchoff, &matchlen, pos) <= 0)
 152                 return 0;
 153
 154         if (!nf_nat_mangle_udp_packet(pskb, ct, ctinfo,
 155                                       matchoff, matchlen, buffer, bufflen))
 156                 return 0;
 157
 158         /* We need to reload this. Thanks Patrick. */
 159         *dptr = (*pskb)->data + ip_hdrlen(*pskb) + sizeof(struct udphdr);
 160         return 1;
 161 }
 162
 163 static int mangle_content_len(struct sk_buff **pskb,
 164                               enum ip_conntrack_info ctinfo,
 165                               struct nf_conn *ct,
 166                               const char *dptr)
 167 {
 168         unsigned int dataoff, matchoff, matchlen;
 169         char buffer[sizeof("65536")];
 170         int bufflen;
 171
 172         dataoff = ip_hdrlen(*pskb) + sizeof(struct udphdr);
 173
 174         /* Get actual SDP lenght */
 175         if (ct_sip_get_info(ct, dptr, (*pskb)->len - dataoff, &matchoff,
 176                             &matchlen, POS_SDP_HEADER) > 0) {
 177
 178                 /* since ct_sip_get_info() give us a pointer passing 'v='
 179                    we need to add 2 bytes in this count. */
 180                 int c_len = (*pskb)->len - dataoff - matchoff + 2;
 181
 182                 /* Now, update SDP length */
 183                 if (ct_sip_get_info(ct, dptr, (*pskb)->len - dataoff, &matchoff,
 184                                     &matchlen, POS_CONTENT) > 0) {
 185
 186                         bufflen = sprintf(buffer, "%u", c_len);
 187                         return nf_nat_mangle_udp_packet(pskb, ct, ctinfo,
 188                                                         matchoff, matchlen,
 189                                                         buffer, bufflen);
 190                 }
 191         }
 192         return 0;
 193 }
 194
 195 static unsigned int mangle_sdp(struct sk_buff **pskb,
 196                                enum ip_conntrack_info ctinfo,
 197                                struct nf_conn *ct,
 198                                __be32 newip, u_int16_t port,
 199                                const char *dptr)
 200 {
 201         char buffer[sizeof("nnn.nnn.nnn.nnn")];
 202         unsigned int dataoff, bufflen;
 203
 204         dataoff = ip_hdrlen(*pskb) + sizeof(struct udphdr);
 205
 206         /* Mangle owner and contact info. */
 207         bufflen = sprintf(buffer, "%u.%u.%u.%u", NIPQUAD(newip));
 208         if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
 209                                buffer, bufflen, POS_OWNER_IP4))
 210                 return 0;
 211
 212         if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
 213                                buffer, bufflen, POS_CONNECTION_IP4))
 214                 return 0;
 215
 216         /* Mangle media port. */
 217         bufflen = sprintf(buffer, "%u", port);
 218         if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
 219                                buffer, bufflen, POS_MEDIA))
 220                 return 0;
 221
 222         return mangle_content_len(pskb, ctinfo, ct, dptr);
 223 }
 224
 225 /* So, this packet has hit the connection tracking matching code.
 226    Mangle it, and change the expectation to match the new version. */
 227 static unsigned int ip_nat_sdp(struct sk_buff **pskb,
 228                                enum ip_conntrack_info ctinfo,
 229                                struct nf_conntrack_expect *exp,
 230                                const char *dptr)
 231 {
 232         struct nf_conn *ct = exp->master;
 233         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 234         __be32 newip;
 235         u_int16_t port;
 236
 237         DEBUGP("ip_nat_sdp():\n");
 238
 239         /* Connection will come from reply */
 240         newip = ct->tuplehash[!dir].tuple.dst.u3.ip;
 241
 242         exp->tuple.dst.u3.ip = newip;
 243         exp->saved_proto.udp.port = exp->tuple.dst.u.udp.port;
 244         exp->dir = !dir;
 245
 246         /* When you see the packet, we need to NAT it the same as the
 247            this one. */
 248         exp->expectfn = nf_nat_follow_master;
 249
 250         /* Try to get same port: if not, try to change it. */
 251         for (port = ntohs(exp->saved_proto.udp.port); port != 0; port++) {
 252                 exp->tuple.dst.u.udp.port = htons(port);
 253                 if (nf_conntrack_expect_related(exp) == 0)
 254                         break;
 255         }
 256
 257         if (port == 0)
 258                 return NF_DROP;
 259
 260         if (!mangle_sdp(pskb, ctinfo, ct, newip, port, dptr)) {
 261                 nf_conntrack_unexpect_related(exp);
 262                 return NF_DROP;
 263         }
 264         return NF_ACCEPT;
 265 }
 266
 267 static void __exit nf_nat_sip_fini(void)
 268 {
 269         rcu_assign_pointer(nf_nat_sip_hook, NULL);
 270         rcu_assign_pointer(nf_nat_sdp_hook, NULL);
 271         synchronize_rcu();
 272 }
 273
 274 static int __init nf_nat_sip_init(void)
 275 {
 276         BUG_ON(rcu_dereference(nf_nat_sip_hook));
 277         BUG_ON(rcu_dereference(nf_nat_sdp_hook));
 278         rcu_assign_pointer(nf_nat_sip_hook, ip_nat_sip);
 279         rcu_assign_pointer(nf_nat_sdp_hook, ip_nat_sdp);
 280         return 0;
 281 }
 282
 283 module_init(nf_nat_sip_init);
 284 module_exit(nf_nat_sip_fini);