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 issue was seen on a Cisco CP-7965G, firmware 8-5(3). It appears to be a well-known problem on 7941 and newer: http://www.voip-info.org/wiki/view/Standalone+Cisco+7941%252F7961+without+a+local+PBX Search for "Connecting to the outside world" I contacted Cisco support and they were not amenable to changing the behavior. It appears to be RFC3261-compliant, as the "Sent-by port" field in the request specifies 5060: 18.2.2 Sending Responses The server transport uses the value of the top Via header field in order to determine where to send a response. It MUST follow the following process: ... o Otherwise (for unreliable unicast transports), if the top Via has a "received" parameter, the response MUST be sent to the address in the "received" parameter, using the port indicated in the "sent-by" value, or using port 5060 if none is specified explicitly. If this fails, for example, elicits an ICMP "port unreachable" response, the procedures of Section 5 of [4] SHOULD be used to determine where to send the response. This patch modifies nf_*_sip to work around this quirk, by rewriting the response port to 5060 when the following conditions are met: - User-Agent starts with "Cisco" - Incoming TTL was exactly 64 (meaning that our system is the phone's local router, not an intermediate router) Tested on Linus' latest 2.6.37-rc tree. Signed-off-by: Kevin Cernekee <cernekee@xxxxxxxxx> --- include/linux/netfilter/nf_conntrack_sip.h | 2 ++ net/ipv4/netfilter/nf_nat_sip.c | 12 ++++++++++++ net/netfilter/nf_conntrack_sip.c | 25 +++++++++++++++++++++++++ 3 files changed, 39 insertions(+), 0 deletions(-) diff --git a/include/linux/netfilter/nf_conntrack_sip.h b/include/linux/netfilter/nf_conntrack_sip.h index 0ce91d5..a6ea620 100644 --- a/include/linux/netfilter/nf_conntrack_sip.h +++ b/include/linux/netfilter/nf_conntrack_sip.h @@ -8,6 +8,7 @@ struct nf_ct_sip_master { unsigned int register_cseq; unsigned int invite_cseq; + unsigned int cisco_port_mangle; }; enum sip_expectation_classes { @@ -90,6 +91,7 @@ enum sip_header_types { SIP_HDR_EXPIRES, SIP_HDR_CONTENT_LENGTH, SIP_HDR_CALL_ID, + SIP_HDR_USER_AGENT, }; enum sdp_header_types { diff --git a/net/ipv4/netfilter/nf_nat_sip.c b/net/ipv4/netfilter/nf_nat_sip.c index e40cf78..4b9a46d 100644 --- a/net/ipv4/netfilter/nf_nat_sip.c +++ b/net/ipv4/netfilter/nf_nat_sip.c @@ -121,6 +121,7 @@ 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; @@ -225,6 +226,17 @@ next: return NF_DROP; } + /* Mangle destination port for Cisco phones, then fix up checksums */ + if (help->help.ct_sip_info.cisco_port_mangle) { + struct udphdr *uh; + + uh = (struct udphdr *)(skb->data + ip_hdrlen(skb)); + uh->dest = htons(SIP_PORT); + + if (!nf_nat_mangle_udp_packet(skb, ct, ctinfo, 0, 0, NULL, 0)) + return NF_DROP; + } + if (!map_sip_addr(skb, dataoff, dptr, datalen, SIP_HDR_FROM) || !map_sip_addr(skb, dataoff, dptr, datalen, SIP_HDR_TO)) return NF_DROP; diff --git a/net/netfilter/nf_conntrack_sip.c b/net/netfilter/nf_conntrack_sip.c index bcf47eb..6042f66 100644 --- a/net/netfilter/nf_conntrack_sip.c +++ b/net/netfilter/nf_conntrack_sip.c @@ -18,6 +18,7 @@ #include <linux/udp.h> #include <linux/tcp.h> #include <linux/netfilter.h> +#include <linux/ip.h> #include <net/netfilter/nf_conntrack.h> #include <net/netfilter/nf_conntrack_core.h> @@ -338,6 +339,7 @@ static const struct sip_header ct_sip_hdrs[] = { [SIP_HDR_EXPIRES] = SIP_HDR("Expires", NULL, NULL, digits_len), [SIP_HDR_CONTENT_LENGTH] = SIP_HDR("Content-Length", "l", NULL, digits_len), [SIP_HDR_CALL_ID] = SIP_HDR("Call-Id", "i", NULL, callid_len), + [SIP_HDR_USER_AGENT] = SIP_HDR("User-Agent", NULL, NULL, string_len), }; static const char *sip_follow_continuation(const char *dptr, const char *limit) @@ -1366,6 +1368,29 @@ static int process_sip_request(struct sk_buff *skb, unsigned int dataoff, unsigned int matchoff, matchlen; unsigned int cseq, i; + /* 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, flag the connection here so that + * responses will be redirected to the correct port. + */ + do { + static const char cisco[] = "Cisco"; + struct iphdr *iph = ip_hdr(skb); + struct nf_conn_help *help = nfct_help(ct); + + if (iph->ttl != 63) + break; + if (ct_sip_get_header(ct, *dptr, 0, *datalen, + SIP_HDR_USER_AGENT, &matchoff, &matchlen) <= 0) + break; + if (matchlen < strlen(cisco)) + break; + if (strnicmp(*dptr + matchoff, cisco, strlen(cisco)) != 0) + break; + + help->help.ct_sip_info.cisco_port_mangle = 1; + } while (0); + for (i = 0; i < ARRAY_SIZE(sip_handlers); i++) { const struct sip_handler *handler; -- 1.7.0.4 -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
