[PATCH/RFC 03/13] Don't do the TCP socket lookup if we already have one attached

[KOVACS Krisztian <hidden@balabit.hu>]

TCP input code path looks up the TCP 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/tcp_ipv4.c |   13 ++++++++++---
 1 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 0ba74bb..536db7b 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1647,9 +1647,16 @@ int tcp_v4_rcv(struct sk_buff *skb)
 	TCP_SKB_CB(skb)->flags	 = skb->nh.iph->tos;
 	TCP_SKB_CB(skb)->sacked	 = 0;
 
-	sk = __inet_lookup(&tcp_hashinfo, skb->nh.iph->saddr, th->source,
-			   skb->nh.iph->daddr, th->dest,
-			   inet_iif(skb));
+	if (unlikely(skb->sk)) {
+		/* steal reference */
+		sk = skb->sk;
+		skb->destructor = NULL;
+		skb->sk = NULL;
+	} else {
+		sk = __inet_lookup(&tcp_hashinfo, skb->nh.iph->saddr, th->source,
+				   skb->nh.iph->daddr, th->dest,
+				   inet_iif(skb));
+	}
 
 	if (!sk)
 		goto no_tcp_socket;