linux-kernel - Re: [PATCH net-2.6 resent] af_packet: Don't use skb after dev_queue

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Message-ID: <20100110222129.GA3606@del.dom.local>
Date:	Sun, 10 Jan 2010 23:21:29 +0100
From:	Jarek Poplawski <jarkao2@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	mbreuer@...jas.com, shemminger@...tta.com,
	akpm@...ux-foundation.org, flyboy@...il.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-2.6 resent] af_packet: Don't use skb after
 dev_queue_xmit()

On Sun, Jan 10, 2010 at 01:51:35PM -0800, David Miller wrote:
> From: Jarek Poplawski <jarkao2@...il.com>
> Date: Sat, 9 Jan 2010 13:38:27 +0100
> 
> > tpacket_snd() can change and kfree an skb after dev_queue_xmit(),
> > which is illegal.
> > 
> > With debugging by: Stephen Hemminger <shemminger@...tta.com>
> > 
> > Reported-by: Michael Breuer <mbreuer@...jas.com>
> > Tested-by: Michael Breuer <mbreuer@...jas.com>
> > Signed-off-by: Jarek Poplawski <jarkao2@...il.com>
> > Acked-by: Stephen Hemminger <shemminger@...tta.com>
> 
> Jarek, if this code path triggers, it will deadlock the
> send ring with your changes.
> 
> We will now leave the ring packet status in the "SENDING" state.
> 
> That's not right.

No, the destructor of this skb, tpacket_destruct_skb(), will clean
this. (Just like for other skbs kfreed during dev_queue_xmit().)

Jarek P.
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