[PATCH/RFC 04/13] Don't do the UDP socket lookup if we already have one attached

[KOVACS Krisztian <hidden@balabit.hu>]

UDP input code path looks up the UDP socket hash tables to find a
socket matching the incoming packet. However, as iptable_tproxy does
socket lookups early the skb may already have the appropriate
reference attached, in that case we steal that reference instead of
doing the lookup.

Signed-off-by: KOVACS Krisztian <hidden@balabit.hu>

---

 net/ipv4/udp.c |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index ce6c460..1d15edc 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1226,8 +1226,15 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct hlist_head udptable[],
 	if(rt->rt_flags & (RTCF_BROADCAST|RTCF_MULTICAST))
 		return __udp4_lib_mcast_deliver(skb, uh, saddr, daddr, udptable);
 
-	sk = __udp4_lib_lookup(saddr, uh->source, daddr, uh->dest,
-			       skb->dev->ifindex, udptable        );
+	if (skb->sk) {
+		/* steal reference */
+		sk = skb->sk;
+		skb->destructor = NULL;
+		skb->sk = NULL;
+	} else {
+		sk = __udp4_lib_lookup(saddr, uh->source, daddr, uh->dest,
+				       skb->dev->ifindex, udptable        );
+	}
 
 	if (sk != NULL) {
 		int ret = udp_queue_rcv_skb(sk, skb);