linux-kernel - Re: [BUG] A panic caused by null pointer dereference aftering updating to

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Message-ID: <1397497204.4222.28.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 14 Apr 2014 10:40:04 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	nasa4836@...il.com, jchapman@...alix.com, edumazet@...gle.com,
	joe@...ches.com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [BUG] A panic caused by null pointer dereference aftering
 updating to

On Mon, 2014-04-14 at 13:34 -0400, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Mon, 14 Apr 2014 10:12:29 -0700
> 
> > Hmm, it seems commit 31c70d5956fc l2tp: keep original skb ownership
> > is the problem.
> > 
> > ip_queue_xmit() assumes the socket attached to skb is an inet socket.
> 
> This is similar to the "send over AF_PACKET" issue we were discussing
> the other week.
> 
> It seems we need a real resolution to this issue.
> 
> To recap:
> 
> 1) We want to charge memory to the top-level socket.
> 
> 2) However during encapsulations etc. we can end up in IP stack
>    which expects only IP sockets to be attached to skb->sk
> 
> I suspect that in the short term we may have to bit the bullet and
> compromise #2, and do flow control via the tunnel's socket.

Or add a sk parameter to ip_queue_xmit(), to break the assumption "sk =
skb->sk", which happened to be generally true, but is ambiguous for IP
tunnels.



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