inet: Don't lookup the socket if there's a socket attached to the skb

Use the socket cached in the skb if it's present.

Signed-off-by: KOVACS Krisztian <hidden@sch.bme.hu>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index c7a90b5..822c9de 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -306,11 +306,15 @@
 						 __be16 sport, __be16 dport,
 						 struct hlist_head udptable[])
 {
+	struct sock *sk;
 	const struct iphdr *iph = ip_hdr(skb);
 
-	return __udp4_lib_lookup(dev_net(skb->dst->dev), iph->saddr, sport,
-				 iph->daddr, dport, inet_iif(skb),
-				 udptable);
+	if (unlikely(sk = skb_steal_sock(skb)))
+		return sk;
+	else
+		return __udp4_lib_lookup(dev_net(skb->dst->dev), iph->saddr, sport,
+					 iph->daddr, dport, inet_iif(skb),
+					 udptable);
 }
 
 struct sock *udp4_lib_lookup(struct net *net, __be32 saddr, __be16 sport,