From 724d0d32fa2a6242a0f03c1baeb8310e7ddcf9a9 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 12 Jun 2014 16:13:06 -0700 Subject: [PATCH] udp: ipv4: do not waste time in __udp4_lib_mcast_demux_lookup [ Upstream commit 63c6f81cdde58c41da62a8d8a209592e42a0203e ] 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: 421b3885bf6d5 ("udp: ipv4: Add udp early demux") Signed-off-by: Eric Dumazet Reported-by: David Held Cc: Shawn Bohrer Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/ipv4/udp.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index 77bd16f..b25e852 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1833,6 +1833,10 @@ 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; -- 2.7.4