netfilter: nf_ct_sip: support Cisco 7941/7945 IP phones

Most SIP devices use a source port of 5060/udp on SIP requests, so the
response automatically comes back to port 5060:

    phone_ip:5060 -> proxy_ip:5060   REGISTER
    proxy_ip:5060 -> phone_ip:5060   100 Trying

The newer Cisco IP phones, however, use a randomly chosen high source
port for the SIP request but expect the response on port 5060:

    phone_ip:49173 -> proxy_ip:5060  REGISTER
    proxy_ip:5060 -> phone_ip:5060   100 Trying

Standard Linux NAT, with or without nf_nat_sip, will send the reply back
to port 49173, not 5060:

    phone_ip:49173 -> proxy_ip:5060  REGISTER
    proxy_ip:5060 -> phone_ip:49173  100 Trying

But the phone is not listening on 49173, so it will never see the reply.

This patch modifies nf_*_sip to work around this quirk by extracting
the SIP response port from the Via: header, iff the source IP in the
packet header matches the source IP in the SIP request.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Patrick McHardy <kaber@trash.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/include/linux/netfilter/nf_conntrack_sip.h b/include/linux/netfilter/nf_conntrack_sip.h
index 387bdd0..ba7f571 100644 (file)
--- a/include/linux/netfilter/nf_conntrack_sip.h
+++ b/include/linux/netfilter/nf_conntrack_sip.h
@@ -4,12 +4,15 @@
 
 #include <net/netfilter/nf_conntrack_expect.h>
 
+#include <linux/types.h>
+
 #define SIP_PORT       5060
 #define SIP_TIMEOUT    3600
 
 struct nf_ct_sip_master {
        unsigned int    register_cseq;
        unsigned int    invite_cseq;
+       __be16          forced_dport;
 };
 
 enum sip_expectation_classes {

diff --git a/net/netfilter/nf_conntrack_sip.c b/net/netfilter/nf_conntrack_sip.c
index df8f4f2..72a67bb 100644 (file)
--- a/net/netfilter/nf_conntrack_sip.c
+++ b/net/netfilter/nf_conntrack_sip.c
@@ -1440,8 +1440,25 @@ static int process_sip_request(struct sk_buff *skb, unsigned int protoff,
 {
        enum ip_conntrack_info ctinfo;
        struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
+       struct nf_ct_sip_master *ct_sip_info = nfct_help_data(ct);
+       enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
        unsigned int matchoff, matchlen;
        unsigned int cseq, i;
+       union nf_inet_addr addr;
+       __be16 port;
+
+       /* Many Cisco IP phones use a high source port for SIP requests, but
+        * listen for the response on port 5060.  If we are the local
+        * router for one of these phones, save the port number from the
+        * Via: header so that nf_nat_sip can redirect the responses to
+        * the correct port.
+        */
+       if (ct_sip_parse_header_uri(ct, *dptr, NULL, *datalen,
+                                   SIP_HDR_VIA_UDP, NULL, &matchoff,
+                                   &matchlen, &addr, &port) > 0 &&
+           port != ct->tuplehash[dir].tuple.src.u.udp.port &&
+           nf_inet_addr_cmp(&addr, &ct->tuplehash[dir].tuple.src.u3))
+               ct_sip_info->forced_dport = port;
 
        for (i = 0; i < ARRAY_SIZE(sip_handlers); i++) {
                const struct sip_handler *handler;

diff --git a/net/netfilter/nf_nat_sip.c b/net/netfilter/nf_nat_sip.c
index 16303c7..5951146 100644 (file)
--- a/net/netfilter/nf_nat_sip.c
+++ b/net/netfilter/nf_nat_sip.c
@@ -95,6 +95,7 @@ static int map_addr(struct sk_buff *skb, unsigned int protoff,
        enum ip_conntrack_info ctinfo;
        struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
        enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
+       struct nf_ct_sip_master *ct_sip_info = nfct_help_data(ct);
        char buffer[INET6_ADDRSTRLEN + sizeof("[]:nnnnn")];
        unsigned int buflen;
        union nf_inet_addr newaddr;
@@ -107,7 +108,8 @@ static int map_addr(struct sk_buff *skb, unsigned int protoff,
        } else if (nf_inet_addr_cmp(&ct->tuplehash[dir].tuple.dst.u3, addr) &&
                   ct->tuplehash[dir].tuple.dst.u.udp.port == port) {
                newaddr = ct->tuplehash[!dir].tuple.src.u3;
-               newport = ct->tuplehash[!dir].tuple.src.u.udp.port;
+               newport = ct_sip_info->forced_dport ? :
+                         ct->tuplehash[!dir].tuple.src.u.udp.port;
        } else
                return 1;
 
@@ -144,6 +146,7 @@ static unsigned int nf_nat_sip(struct sk_buff *skb, unsigned int protoff,
        enum ip_conntrack_info ctinfo;
        struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
        enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
+       struct nf_ct_sip_master *ct_sip_info = nfct_help_data(ct);
        unsigned int coff, matchoff, matchlen;
        enum sip_header_types hdr;
        union nf_inet_addr addr;
@@ -258,6 +261,21 @@ next:
            !map_sip_addr(skb, protoff, dataoff, dptr, datalen, SIP_HDR_TO))
                return NF_DROP;
 
+       /* Mangle destination port for Cisco phones, then fix up checksums */
+       if (dir == IP_CT_DIR_REPLY && ct_sip_info->forced_dport) {
+               struct udphdr *uh;
+
+               if (!skb_make_writable(skb, skb->len))
+                       return NF_DROP;
+
+               uh = (void *)skb->data + protoff;
+               uh->dest = ct_sip_info->forced_dport;
+
+               if (!nf_nat_mangle_udp_packet(skb, ct, ctinfo, protoff,
+                                             0, 0, NULL, 0))
+                       return NF_DROP;
+       }
+
        return NF_ACCEPT;
 }
 
@@ -311,8 +329,10 @@ static unsigned int nf_nat_sip_expect(struct sk_buff *skb, unsigned int protoff,
        enum ip_conntrack_info ctinfo;
        struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
        enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
+       struct nf_ct_sip_master *ct_sip_info = nfct_help_data(ct);
        union nf_inet_addr newaddr;
        u_int16_t port;
+       __be16 srcport;
        char buffer[INET6_ADDRSTRLEN + sizeof("[]:nnnnn")];
        unsigned int buflen;
 
@@ -326,8 +346,9 @@ static unsigned int nf_nat_sip_expect(struct sk_buff *skb, unsigned int protoff,
        /* 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)
+       srcport = ct_sip_info->forced_dport ? :
+                 ct->tuplehash[dir].tuple.src.u.udp.port;
+       if (exp->tuple.dst.u.udp.port == srcport)
                port = ntohs(ct->tuplehash[!dir].tuple.dst.u.udp.port);
        else
                port = ntohs(exp->tuple.dst.u.udp.port);