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Subject[PATCH v3] netfilter: nf_conntrack_sip: Handle Cisco 7941/7945 IP phones
Date
[v3:
Only activate the new forced_dport logic if the IP matches, but the
port does not. ]

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>
---
include/linux/netfilter/nf_conntrack_sip.h | 3 +++
net/ipv4/netfilter/nf_nat_sip.c | 26 +++++++++++++++++++++++---
net/netfilter/nf_conntrack_sip.c | 17 +++++++++++++++++
3 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/include/linux/netfilter/nf_conntrack_sip.h b/include/linux/netfilter/nf_conntrack_sip.h
index 0ce91d5..feda699 100644
--- a/include/linux/netfilter/nf_conntrack_sip.h
+++ b/include/linux/netfilter/nf_conntrack_sip.h
@@ -2,12 +2,15 @@
#define __NF_CONNTRACK_SIP_H__
#ifdef __KERNEL__

+#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/ipv4/netfilter/nf_nat_sip.c b/net/ipv4/netfilter/nf_nat_sip.c
index e40cf78..e5856b0 100644
--- a/net/ipv4/netfilter/nf_nat_sip.c
+++ b/net/ipv4/netfilter/nf_nat_sip.c
@@ -73,6 +73,7 @@ static int map_addr(struct sk_buff *skb, unsigned int dataoff,
enum ip_conntrack_info ctinfo;
struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
+ struct nf_conn_help *help = nfct_help(ct);
char buffer[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
unsigned int buflen;
__be32 newaddr;
@@ -85,7 +86,8 @@ static int map_addr(struct sk_buff *skb, unsigned int dataoff,
} 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;
+ newport = help->help.ct_sip_info.forced_dport ? :
+ ct->tuplehash[!dir].tuple.src.u.udp.port;
} else
return 1;

@@ -121,6 +123,7 @@ static unsigned int ip_nat_sip(struct sk_buff *skb, unsigned int dataoff,
enum ip_conntrack_info ctinfo;
struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
+ struct nf_conn_help *help = nfct_help(ct);
unsigned int coff, matchoff, matchlen;
enum sip_header_types hdr;
union nf_inet_addr addr;
@@ -229,6 +232,20 @@ next:
!map_sip_addr(skb, 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 && help->help.ct_sip_info.forced_dport) {
+ struct udphdr *uh;
+
+ if (!skb_make_writable(skb, skb->len))
+ return NF_DROP;
+
+ uh = (struct udphdr *)(skb->data + ip_hdrlen(skb));
+ uh->dest = help->help.ct_sip_info.forced_dport;
+
+ if (!nf_nat_mangle_udp_packet(skb, ct, ctinfo, 0, 0, NULL, 0))
+ return NF_DROP;
+ }
+
return NF_ACCEPT;
}

@@ -280,8 +297,10 @@ static unsigned int ip_nat_sip_expect(struct sk_buff *skb, unsigned int dataoff,
enum ip_conntrack_info ctinfo;
struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
+ struct nf_conn_help *help = nfct_help(ct);
__be32 newip;
u_int16_t port;
+ __be16 srcport;
char buffer[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
unsigned buflen;

@@ -294,8 +313,9 @@ static unsigned int ip_nat_sip_expect(struct sk_buff *skb, unsigned int dataoff,
/* 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 = help->help.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);
diff --git a/net/netfilter/nf_conntrack_sip.c b/net/netfilter/nf_conntrack_sip.c
index bcf47eb..776130d 100644
--- a/net/netfilter/nf_conntrack_sip.c
+++ b/net/netfilter/nf_conntrack_sip.c
@@ -1363,8 +1363,25 @@ static int process_sip_request(struct sk_buff *skb, unsigned int dataoff,
{
enum ip_conntrack_info ctinfo;
struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
+ struct nf_conn_help *help = nfct_help(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))
+ help->help.ct_sip_info.forced_dport = port;

for (i = 0; i < ARRAY_SIZE(sip_handlers); i++) {
const struct sip_handler *handler;
--
1.7.0.4


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