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Date: Tue, 16 Jun 2015 07:59:11 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: David Miller <davem@...emloft.net> Cc: netdev <netdev@...r.kernel.org>, Willem de Bruijn <willemb@...gle.com> Subject: [PATCH net] packet: read num_members once in packet_rcv_fanout() From: Eric Dumazet <edumazet@...gle.com> 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@...gle.com> Cc: Willem de Bruijn <willemb@...gle.com> --- Note : I chose to use READ_ONCE() but stable backports should use ACCESS_ONCE() 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 b5989c6ee551..131545a06f05 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1353,7 +1353,7 @@ 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 = READ_ONCE(f->num_members); struct packet_sock *po; unsigned int idx; -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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