netdev - Re: Fix NULL dereference in x25

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Message-ID: <1320200358.4728.28.camel@edumazet-laptop>
Date:	Wed, 02 Nov 2011 03:19:18 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Dave Jones <davej@...hat.com>
Cc:	netdev@...r.kernel.org, Matthew Daley <mattjd@...il.com>
Subject: Re: Fix NULL dereference in x25_recvmsg

Le mardi 01 novembre 2011 à 22:15 -0400, Dave Jones a écrit :
> On Wed, Nov 02, 2011 at 03:10:45AM +0100, Eric Dumazet wrote:
>  > Le mardi 01 novembre 2011 à 21:53 -0400, Dave Jones a écrit :
>  > > commit cb101ed2 in 3.0 introduced a bug in x25_recvmsg()
>  > > When passed bogus junk from userspace, x25->neighbour can be NULL,
>  > > as shown in this oops..
>  > > 
>  > 
>  > Your patch seems fine but :
>  > 
>  > Are you sure this bug is not present on previous kernels ?
>  > 
>  > It seems we had prior to this commit :
>  > 
>  > skb_pull(skb, x25->neighbour->extended ?
>  > 	X25_EXT_MIN_LEN : X25_STD_MIN_LEN);
> 
> It might have been possible with a specifically crafted set of arguments.
> 
> It never showed up in testing before now, probably because we were
> returning from the function before we got to that skb_pull
> via all the other tests that get performed.
> 

neighbour is not an x25_recvmsg() argument, but related to x25 socket
state.

Maybe your tests dont try to use x25_recvmsg() while socket has no
neighbour...

This bug was there before the cb101ed2 commit.


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