udp: ipv4: do not waste time in __udp4_lib_mcast_demux_lookup

Its too easy to add thousand of UDP sockets on a particular bucket, and slow down an innocent multicast receiver. Early demux is supposed to be an optimization, we should avoid spending too much time in it. It is interesting to note __udp4_lib_demux_lookup() only tries to match first socket in the chain. 10 is the threshold we already have in __udp4_lib_lookup() to switch to secondary hash. Fixes: 421b388 ("udp: ipv4: Add udp early demux") Signed-off-by: Eric Dumazet <[email protected]> Reported-by: David Held <[email protected]> Cc: Shawn Bohrer <[email protected]> Signed-off-by: David S. Miller <[email protected]>
niw · Jun 13, 2014 · 63c6f81 · 63c6f81
1 parent 2853af6
commit 63c6f81
Showing 1 changed file with 4 additions and 0 deletions.
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
@@ -1861,6 +1861,10 @@ static struct sock *__udp4_lib_mcast_demux_lookup(struct net *net,
 	unsigned int count, slot = udp_hashfn(net, hnum, udp_table.mask);
 	struct udp_hslot *hslot = &udp_table.hash[slot];
 
+	/* Do not bother scanning a too big list */
+	if (hslot->count > 10)
+		return NULL;
+
 	rcu_read_lock();
 begin:
 	count = 0;