| From | Ben Hutchings <> | Date | Sun, 02 Aug 2015 01:02:38 +0100 | Subject | [PATCH 3.2 137/164] packet: read num_members once in packet_rcv_fanout() |
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3.2.70-rc1 review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet <edumazet@google.com>
[ Upstream commit f98f4514d07871da7a113dd9e3e330743fd70ae4 ]
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 <edumazet@google.com> Cc: Willem de Bruijn <willemb@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- net/packet/af_packet.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1211,7 +1211,7 @@ static int packet_rcv_fanout(struct sk_b 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;
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