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

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Date:	Mon, 14 Apr 2014 13:49:01 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
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

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Mon, 14 Apr 2014 10:40:04 -0700

> 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.

Yep that would handle the l2tp cases, but vxlan needs something different
since it goes through iptunnel_xmit().

So perhaps as a quick fix we can add an 'sk' arg to both
ip_queue_xmit() and ip_local_out().
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