From 2fb9a78c44b0801fb17f3f73f553b8416b96abe0 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 16 Jun 2015 07:59:11 -0700 Subject: [PATCH] packet: read num_members once in packet_rcv_fanout() commit f98f4514d07871da7a113dd9e3e330743fd70ae4 upstream. We need to tell compiler it must not read f->num_members multiple times. Otherwise testing if num is not zero is flaky, and we could attempt an invalid divide by 0 in fanout_demux_cpu() Note bug was present in packet_rcv_fanout_hash() and packet_rcv_fanout_lb() but final 3.1 had a simple location after commit 95ec3eb417115fb ("packet: Add 'cpu' fanout policy.") Fixes: dc99f600698dc ("packet: Add fanout support.") Signed-off-by: Eric Dumazet Cc: Willem de Bruijn Signed-off-by: David S. Miller [lizf: Backported to 3.4: use ACCESS_ONCE() instead of READ_ONCE()] Signed-off-by: Zefan Li --- net/packet/af_packet.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index dbe1715c629fd..af067d72dff3b 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1210,7 +1210,7 @@ static int packet_rcv_fanout(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt, struct net_device *orig_dev) { struct packet_fanout *f = pt->af_packet_priv; - unsigned int num = f->num_members; + unsigned int num = ACCESS_ONCE(f->num_members); struct packet_sock *po; struct sock *sk; -- 2.47.2