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Commit 7266507d authored by Kevin Cernekee's avatar Kevin Cernekee Committed by Pablo Neira Ayuso
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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: default avatarKevin Cernekee <cernekee@gmail.com>
Acked-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Cc: Patrick McHardy <kaber@trash.net>
Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
parent 247fa82b

include/linux/netfilter/nf_conntrack_sip.h

+3 −0
Original line number Diff line number Diff line
@@ -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 {

net/netfilter/nf_conntrack_sip.c

+17 −0
Original line number Diff line number Diff line
@@ -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;

net/netfilter/nf_nat_sip.c

+24 −3
Original line number Diff line number Diff line
@@ -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 @@ static unsigned int nf_nat_sip(struct sk_buff *skb, unsigned int protoff, 
	    !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);