netdev - Re: [PATCH 1/1] Revert "af-packet: Use existing netdev reference for bound sockets"

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Message-Id: <20131118.130310.1183708218770881544.davem@davemloft.net>
Date:	Mon, 18 Nov 2013 13:03:10 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	dborkman@...hat.com
Cc:	noureddine@...stanetworks.com, willemb@...gle.com, phil@....cc,
	edumazet@...gle.com, netdev@...r.kernel.org,
	greearb@...delatech.com
Subject: Re: [PATCH 1/1] Revert "af-packet: Use existing netdev reference
 for bound sockets"

From: Daniel Borkmann <dborkman@...hat.com>
Date: Mon, 18 Nov 2013 10:00:53 +0100

> On 11/18/2013 08:40 AM, Salam Noureddine wrote:
>> This reverts commit 827d978037d7d0bf0860481948c6d26ead10042f
>> ("af-packet: Use existing netdev reference for bound sockets")
>>
>> The patch introduced a race condition between packet_snd and
>> packet_notifier when a net_device is being unregistered. In the case
>> of
>> a bound socket, packet_notifier can drop the last reference to the
>> net_device and packet_snd might end up sending a packet over a freed
>> net_device.
> 
> So there's no other workaround possible like e.g. setting a flag in
> struct packet_sock so that in case our netdevice goes down, we just
> set the flag and if set, we return with -ENXIO in send path?
> Reverting this would decrease performance for everyone as we would
> then do the lookup every time we send a packet again.

Agreed, we should try first to find a reasonable fix instead of just
doing a knee-jerk revert of this change.

Thanks.
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