[PATCH v3] netfilter: nf_conntrack_sip: add sip_external_media logic

[Alin Nastac <alin.nastac@xxxxxxxxx>]

From: Alin Nastac <alin.nastac@xxxxxxxxx>

Allow media streams that are not passing through this router.

When enabled, the sip_external_media logic will leave SDP
payload untouched when it detects that interface towards INVITEd
party is the same with the one towards media endpoint.

Signed-off-by: Alin Nastac <alin.nastac@xxxxxxxxx>
---
 net/netfilter/nf_conntrack_sip.c | 42 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/net/netfilter/nf_conntrack_sip.c b/net/netfilter/nf_conntrack_sip.c
index c8d2b66..f067c6b 100644
--- a/net/netfilter/nf_conntrack_sip.c
+++ b/net/netfilter/nf_conntrack_sip.c
@@ -21,6 +21,8 @@
 #include <linux/tcp.h>
 #include <linux/netfilter.h>
 
+#include <net/route.h>
+#include <net/ip6_route.h>
 #include <net/netfilter/nf_conntrack.h>
 #include <net/netfilter/nf_conntrack_core.h>
 #include <net/netfilter/nf_conntrack_expect.h>
@@ -54,6 +56,11 @@ module_param(sip_direct_media, int, 0600);
 MODULE_PARM_DESC(sip_direct_media, "Expect Media streams between signalling "
 				   "endpoints only (default 1)");
 
+static int sip_external_media __read_mostly = 0;
+module_param(sip_external_media, int, 0600);
+MODULE_PARM_DESC(sip_external_media, "Expect Media streams between external "
+				     "endpoints (default 0)");
+
 const struct nf_nat_sip_hooks *nf_nat_sip_hooks;
 EXPORT_SYMBOL_GPL(nf_nat_sip_hooks);
 
@@ -861,6 +868,41 @@ static int set_expected_rtp_rtcp(struct sk_buff *skb, unsigned int protoff,
 		if (!nf_inet_addr_cmp(daddr, &ct->tuplehash[dir].tuple.src.u3))
 			return NF_ACCEPT;
 		saddr = &ct->tuplehash[!dir].tuple.src.u3;
+	} else if (sip_external_media) {
+		struct net_device *dev = skb_dst(skb)->dev;
+		struct net *net = dev_net(dev);
+		struct rtable *rt;
+		struct flowi4 fl4 = {};
+#if IS_ENABLED(CONFIG_IPV6)
+		struct flowi6 fl6 = {};
+#endif
+		struct dst_entry *dst = NULL;
+
+		switch (nf_ct_l3num(ct)) {
+			case NFPROTO_IPV4:
+				fl4.daddr = daddr->ip;
+				rt = ip_route_output_key(net, &fl4);
+				if (!IS_ERR(rt))
+					dst = &rt->dst;
+				break;
+
+#if IS_ENABLED(CONFIG_IPV6)
+			case NFPROTO_IPV6:
+				fl6.daddr = daddr->in6;
+				dst = ip6_route_output(net, NULL, &fl6);
+				if (dst->error) {
+					dst_release(dst);
+					dst = NULL;
+				}
+				break;
+#endif
+		}
+
+		/* Don't predict any conntracks when media endpoint is reachable
+		 * through the same interface as the signalling peer.
+		 */
+		if (dst && dst->dev == dev)
+			return NF_ACCEPT;
 	}
 
 	/* We need to check whether the registration exists before attempting
-- 
2.7.4