/* SIP extension for UDP NAT alteration. * * (C) 2005 by Christian Hentschel * based on RR's ip_nat_ftp.c and other modules. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. */ #include #include #include #include #include #include #include #include #include #include #include MODULE_LICENSE("GPL"); MODULE_AUTHOR("Christian Hentschel "); MODULE_DESCRIPTION("SIP NAT helper"); MODULE_ALIAS("ip_nat_sip"); static unsigned int mangle_packet(struct sk_buff *skb, const char **dptr, unsigned int *datalen, unsigned int matchoff, unsigned int matchlen, const char *buffer, unsigned int buflen) { enum ip_conntrack_info ctinfo; struct nf_conn *ct = nf_ct_get(skb, &ctinfo); if (!nf_nat_mangle_udp_packet(skb, ct, ctinfo, matchoff, matchlen, buffer, buflen)) return 0; /* Reload data pointer and adjust datalen value */ *dptr = skb->data + ip_hdrlen(skb) + sizeof(struct udphdr); *datalen += buflen - matchlen; return 1; } static int map_addr(struct sk_buff *skb, const char **dptr, unsigned int *datalen, unsigned int matchoff, unsigned int matchlen, union nf_inet_addr *addr, __be16 port) { enum ip_conntrack_info ctinfo; struct nf_conn *ct = nf_ct_get(skb, &ctinfo); enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo); char buffer[sizeof("nnn.nnn.nnn.nnn:nnnnn")]; unsigned int buflen; __be32 newaddr; __be16 newport; if (ct->tuplehash[dir].tuple.src.u3.ip == addr->ip && ct->tuplehash[dir].tuple.src.u.udp.port == port) { newaddr = ct->tuplehash[!dir].tuple.dst.u3.ip; newport = ct->tuplehash[!dir].tuple.dst.u.udp.port; } else if (ct->tuplehash[dir].tuple.dst.u3.ip == addr->ip && ct->tuplehash[dir].tuple.dst.u.udp.port == port) { newaddr = ct->tuplehash[!dir].tuple.src.u3.ip; newport = ct->tuplehash[!dir].tuple.src.u.udp.port; } else return 1; if (newaddr == addr->ip && newport == port) return 1; buflen = sprintf(buffer, "%u.%u.%u.%u:%u", NIPQUAD(newaddr), ntohs(newport)); return mangle_packet(skb, dptr, datalen, matchoff, matchlen, buffer, buflen); } static int map_sip_addr(struct sk_buff *skb, const char **dptr, unsigned int *datalen, enum sip_header_types type) { enum ip_conntrack_info ctinfo; struct nf_conn *ct = nf_ct_get(skb, &ctinfo); unsigned int matchlen, matchoff; union nf_inet_addr addr; __be16 port; if (ct_sip_parse_header_uri(ct, *dptr, NULL, *datalen, type, NULL, &matchoff, &matchlen, &addr, &port) <= 0) return 1; return map_addr(skb, dptr, datalen, matchoff, matchlen, &addr, port); } static unsigned int ip_nat_sip(struct sk_buff *skb, const char **dptr, unsigned int *datalen) { enum ip_conntrack_info ctinfo; struct nf_conn *ct = nf_ct_get(skb, &ctinfo); enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo); unsigned int dataoff, matchoff, matchlen; union nf_inet_addr addr; __be16 port; int request, in_header; /* Basic rules: requests and responses. */ if (strnicmp(*dptr, "SIP/2.0", strlen("SIP/2.0")) != 0) { if (ct_sip_parse_request(ct, *dptr, *datalen, &matchoff, &matchlen, &addr, &port) > 0 && !map_addr(skb, dptr, datalen, matchoff, matchlen, &addr, port)) return NF_DROP; request = 1; } else request = 0; /* Translate topmost Via header and parameters */ if (ct_sip_parse_header_uri(ct, *dptr, NULL, *datalen, SIP_HDR_VIA, NULL, &matchoff, &matchlen, &addr, &port) > 0) { unsigned int matchend, poff, plen, buflen, n; char buffer[sizeof("nnn.nnn.nnn.nnn:nnnnn")]; /* We're only interested in headers related to this * connection */ if (request) { if (addr.ip != ct->tuplehash[dir].tuple.src.u3.ip || port != ct->tuplehash[dir].tuple.src.u.udp.port) goto next; } else { if (addr.ip != ct->tuplehash[dir].tuple.dst.u3.ip || port != ct->tuplehash[dir].tuple.dst.u.udp.port) goto next; } if (!map_addr(skb, dptr, datalen, matchoff, matchlen, &addr, port)) return NF_DROP; matchend = matchoff + matchlen; /* The maddr= parameter (RFC 2361) specifies where to send * the reply. */ if (ct_sip_parse_address_param(ct, *dptr, matchend, *datalen, "maddr=", &poff, &plen, &addr) > 0 && addr.ip == ct->tuplehash[dir].tuple.src.u3.ip && addr.ip != ct->tuplehash[!dir].tuple.dst.u3.ip) { __be32 ip = ct->tuplehash[!dir].tuple.dst.u3.ip; buflen = sprintf(buffer, "%u.%u.%u.%u", NIPQUAD(ip)); if (!mangle_packet(skb, dptr, datalen, poff, plen, buffer, buflen)) return NF_DROP; } /* The received= parameter (RFC 2361) contains the address * from which the server received the request. */ if (ct_sip_parse_address_param(ct, *dptr, matchend, *datalen, "received=", &poff, &plen, &addr) > 0 && addr.ip == ct->tuplehash[dir].tuple.dst.u3.ip && addr.ip != ct->tuplehash[!dir].tuple.src.u3.ip) { __be32 ip = ct->tuplehash[!dir].tuple.src.u3.ip; buflen = sprintf(buffer, "%u.%u.%u.%u", NIPQUAD(ip)); if (!mangle_packet(skb, dptr, datalen, poff, plen, buffer, buflen)) return NF_DROP; } /* The rport= parameter (RFC 3581) contains the port number * from which the server received the request. */ if (ct_sip_parse_numerical_param(ct, *dptr, matchend, *datalen, "rport=", &poff, &plen, &n) > 0 && htons(n) == ct->tuplehash[dir].tuple.dst.u.udp.port && htons(n) != ct->tuplehash[!dir].tuple.src.u.udp.port) { __be16 p = ct->tuplehash[!dir].tuple.src.u.udp.port; buflen = sprintf(buffer, "%u", ntohs(p)); if (!mangle_packet(skb, dptr, datalen, poff, plen, buffer, buflen)) return NF_DROP; } } next: /* Translate Contact headers */ dataoff = 0; in_header = 0; while (ct_sip_parse_header_uri(ct, *dptr, &dataoff, *datalen, SIP_HDR_CONTACT, &in_header, &matchoff, &matchlen, &addr, &port) > 0) { if (!map_addr(skb, dptr, datalen, matchoff, matchlen, &addr, port)) return NF_DROP; } if (!map_sip_addr(skb, dptr, datalen, SIP_HDR_FROM) || !map_sip_addr(skb, dptr, datalen, SIP_HDR_TO)) return NF_DROP; return NF_ACCEPT; } /* Handles expected signalling connections and media streams */ static void ip_nat_sip_expected(struct nf_conn *ct, struct nf_conntrack_expect *exp) { struct nf_nat_range range; /* This must be a fresh one. */ BUG_ON(ct->status & IPS_NAT_DONE_MASK); /* For DST manip, map port here to where it's expected. */ range.flags = (IP_NAT_RANGE_MAP_IPS | IP_NAT_RANGE_PROTO_SPECIFIED); range.min = range.max = exp->saved_proto; range.min_ip = range.max_ip = exp->saved_ip; nf_nat_setup_info(ct, &range, IP_NAT_MANIP_DST); /* Change src to where master sends to, but only if the connection * actually came from the same source. */ if (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip == ct->master->tuplehash[exp->dir].tuple.src.u3.ip) { range.flags = IP_NAT_RANGE_MAP_IPS; range.min_ip = range.max_ip = ct->master->tuplehash[!exp->dir].tuple.dst.u3.ip; nf_nat_setup_info(ct, &range, IP_NAT_MANIP_SRC); } } static unsigned int ip_nat_sip_expect(struct sk_buff *skb, const char **dptr, unsigned int *datalen, struct nf_conntrack_expect *exp, unsigned int matchoff, unsigned int matchlen) { enum ip_conntrack_info ctinfo; struct nf_conn *ct = nf_ct_get(skb, &ctinfo); enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo); __be32 newip; u_int16_t port; char buffer[sizeof("nnn.nnn.nnn.nnn:nnnnn")]; unsigned buflen; /* Connection will come from reply */ if (ct->tuplehash[dir].tuple.src.u3.ip == ct->tuplehash[!dir].tuple.dst.u3.ip) newip = exp->tuple.dst.u3.ip; else newip = ct->tuplehash[!dir].tuple.dst.u3.ip; /* If the signalling port matches the connection's source port in the * original direction, try to use the destination port in the opposite * direction. */ if (exp->tuple.dst.u.udp.port == ct->tuplehash[dir].tuple.src.u.udp.port) port = ntohs(ct->tuplehash[!dir].tuple.dst.u.udp.port); else port = ntohs(exp->tuple.dst.u.udp.port); exp->saved_ip = exp->tuple.dst.u3.ip; exp->tuple.dst.u3.ip = newip; exp->saved_proto.udp.port = exp->tuple.dst.u.udp.port; exp->dir = !dir; exp->expectfn = ip_nat_sip_expected; for (; port != 0; port++) { exp->tuple.dst.u.udp.port = htons(port); if (nf_ct_expect_related(exp) == 0) break; } if (port == 0) return NF_DROP; if (exp->tuple.dst.u3.ip != exp->saved_ip || exp->tuple.dst.u.udp.port != exp->saved_proto.udp.port) { buflen = sprintf(buffer, "%u.%u.%u.%u:%u", NIPQUAD(newip), port); if (!mangle_packet(skb, dptr, datalen, matchoff, matchlen, buffer, buflen)) goto err; } return NF_ACCEPT; err: nf_ct_unexpect_related(exp); return NF_DROP; } static int mangle_content_len(struct sk_buff *skb, const char **dptr, unsigned int *datalen) { enum ip_conntrack_info ctinfo; struct nf_conn *ct = nf_ct_get(skb, &ctinfo); unsigned int matchoff, matchlen; char buffer[sizeof("65536")]; int buflen, c_len; /* Get actual SDP length */ if (ct_sip_get_sdp_header(ct, *dptr, 0, *datalen, SDP_HDR_VERSION, SDP_HDR_UNSPEC, &matchoff, &matchlen) <= 0) return 0; c_len = *datalen - matchoff + strlen("v="); /* Now, update SDP length */ if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_CONTENT_LENGTH, &matchoff, &matchlen) <= 0) return 0; buflen = sprintf(buffer, "%u", c_len); return mangle_packet(skb, dptr, datalen, matchoff, matchlen, buffer, buflen); } static unsigned mangle_sdp_packet(struct sk_buff *skb, const char **dptr, unsigned int *datalen, enum sdp_header_types type, char *buffer, int buflen) { enum ip_conntrack_info ctinfo; struct nf_conn *ct = nf_ct_get(skb, &ctinfo); unsigned int matchlen, matchoff; if (ct_sip_get_sdp_header(ct, *dptr, 0, *datalen, type, SDP_HDR_UNSPEC, &matchoff, &matchlen) <= 0) return 0; return mangle_packet(skb, dptr, datalen, matchoff, matchlen, buffer, buflen); } static unsigned int mangle_sdp(struct sk_buff *skb, enum ip_conntrack_info ctinfo, struct nf_conn *ct, __be32 newip, u_int16_t port, const char **dptr, unsigned int *datalen) { char buffer[sizeof("nnn.nnn.nnn.nnn")]; unsigned int bufflen; /* Mangle owner and contact info. */ bufflen = sprintf(buffer, "%u.%u.%u.%u", NIPQUAD(newip)); if (!mangle_sdp_packet(skb, dptr, datalen, SDP_HDR_OWNER_IP4, buffer, bufflen)) return 0; if (!mangle_sdp_packet(skb, dptr, datalen, SDP_HDR_CONNECTION_IP4, buffer, bufflen)) return 0; /* Mangle media port. */ bufflen = sprintf(buffer, "%u", port); if (!mangle_sdp_packet(skb, dptr, datalen, SDP_HDR_MEDIA, buffer, bufflen)) return 0; return mangle_content_len(skb, dptr, datalen); } /* So, this packet has hit the connection tracking matching code. Mangle it, and change the expectation to match the new version. */ static unsigned int ip_nat_sdp(struct sk_buff *skb, const char **dptr, unsigned int *datalen, struct nf_conntrack_expect *exp) { enum ip_conntrack_info ctinfo; struct nf_conn *ct = nf_ct_get(skb, &ctinfo); enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo); __be32 newip; u_int16_t port; /* Connection will come from reply */ if (ct->tuplehash[dir].tuple.src.u3.ip == ct->tuplehash[!dir].tuple.dst.u3.ip) newip = exp->tuple.dst.u3.ip; else newip = ct->tuplehash[!dir].tuple.dst.u3.ip; exp->saved_ip = exp->tuple.dst.u3.ip; exp->tuple.dst.u3.ip = newip; exp->saved_proto.udp.port = exp->tuple.dst.u.udp.port; exp->dir = !dir; /* When you see the packet, we need to NAT it the same as the this one. */ exp->expectfn = ip_nat_sip_expected; /* Try to get same port: if not, try to change it. */ for (port = ntohs(exp->saved_proto.udp.port); port != 0; port++) { exp->tuple.dst.u.udp.port = htons(port); if (nf_ct_expect_related(exp) == 0) break; } if (port == 0) return NF_DROP; if (!mangle_sdp(skb, ctinfo, ct, newip, port, dptr, datalen)) { nf_ct_unexpect_related(exp); return NF_DROP; } return NF_ACCEPT; } static void __exit nf_nat_sip_fini(void) { rcu_assign_pointer(nf_nat_sip_hook, NULL); rcu_assign_pointer(nf_nat_sip_expect_hook, NULL); rcu_assign_pointer(nf_nat_sdp_hook, NULL); synchronize_rcu(); } static int __init nf_nat_sip_init(void) { BUG_ON(nf_nat_sip_hook != NULL); BUG_ON(nf_nat_sip_expect_hook != NULL); BUG_ON(nf_nat_sdp_hook != NULL); rcu_assign_pointer(nf_nat_sip_hook, ip_nat_sip); rcu_assign_pointer(nf_nat_sip_expect_hook, ip_nat_sip_expect); rcu_assign_pointer(nf_nat_sdp_hook, ip_nat_sdp); return 0; } module_init(nf_nat_sip_init); module_exit(nf_nat_sip_fini);