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

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Message-ID: <1397499566.4222.36.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 14 Apr 2014 11:19:26 -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 14:02 -0400, David Miller wrote:

> BTW, it occurs to me that there may be some other spots in the output path
> that expect that if SKB is ETH_P_IP then skb->sk is IP socket.  For example
> somewhere in netfilter or packet classifier paths.
> 
> Just FYI... that was one of the things I was going to audit.

packet classifiers cannot have such assumptions for sure.

About iptunnel_xmit(), I do not think there is an issue, as we do not
enter ip_queue_xmit() on this path, but ip_local_out().

ip_local_out() doesn't use skb->sk , unless some netfilter module
uses this. I am not sure how the previous behavior could be useful in
this case, as all packets were sharing same socket ownership.

net/netfilter/xt_owner.c for example has better coverage if it can
really have a pointer to the user socket, not the internal socket used
by l2tp or vxlan tunnel.

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