commit 4971613c16 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: dc99f60069 ("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>
ca3d015d39