From: Willem de Bruijn <willemb@google.com>
Date: Tue, 26 Sep 2017 16:19:37 +0000 (-0400)
Subject: packet: in packet_do_bind, test fanout with bind_lock held
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ca3d015d39f0357889fa3ef6a88028162de17d7d;p=pandora-kernel.git

packet: in packet_do_bind, test fanout with bind_lock held

commit 4971613c1639d8e5f102c4e797c3bf8f83a5a69e upstream.

Once a socket has po->fanout set, it remains a member of the group
until it is destroyed. The prot_hook must be constant and identical
across sockets in the group.

If fanout_add races with packet_do_bind between the test of po->fanout
and taking the lock, the bind call may make type or dev inconsistent
with that of the fanout group.

Hold po->bind_lock when testing po->fanout to avoid this race.

I had to introduce artificial delay (local_bh_enable) to actually
observe the race.

Fixes: dc99f600698d ("packet: Add fanout support.")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

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