netfilter: conntrack: don't deliver events for racy packets

This patch skips the delivery of conntrack events if the packet
was drop due to a race condition in the conntrack insertion.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>

include/net/netfilter/nf_conntrack_core.h

@@ -62,7 +62,8 @@ static inline int nf_conntrack_confirm(struct sk_buff *skb)
 	if (ct && ct != &nf_conntrack_untracked) {
 		if (!nf_ct_is_confirmed(ct) && !nf_ct_is_dying(ct))
 			ret = __nf_conntrack_confirm(skb);
-		nf_ct_deliver_cached_events(ct);
+		if (likely(ret == NF_ACCEPT))
+			nf_ct_deliver_cached_events(ct);
 	}
 	return ret;
 }