netdev - Re: [PATCH net] packet: in packet_do_bind, test fanout with bind

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Message-Id: <20170928.102502.2269082759734068360.davem@davemloft.net>
Date:   Thu, 28 Sep 2017 10:25:02 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     willemdebruijn.kernel@...il.com
Cc:     netdev@...r.kernel.org, willemb@...gle.com
Subject: Re: [PATCH net] packet: in packet_do_bind, test fanout with
 bind_lock held

From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Date: Tue, 26 Sep 2017 12:19:37 -0400

> From: Willem de Bruijn <willemb@...gle.com>
> 
> 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@...gle.com>
> Reviewed-by: Eric Dumazet <edumazet@...gle.com>

Applied and queued up for -stable.