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packet: read num_members once in packet_rcv_fanout()

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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 95ec3eb417 ("packet: Add 'cpu' fanout policy.")

Fixes: dc99f60069 ("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>
[lizf: Backported to 3.4: use ACCESS_ONCE() instead of READ_ONCE()]
Signed-off-by: Zefan Li <lizefan@huawei.com>
This commit is contained in:
Eric Dumazet 2015-06-16 07:59:11 -07:00 committed by Zefan Li
parent b80954b458
commit 2fb9a78c44
1 changed files with 1 additions and 1 deletions
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2
net/packet/af_packet.c
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@ -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;