netdev - Re: PROBLEM: System call 'sendmsg' of process ospfd (quagga) causes kernel oops

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Date:	Wed, 19 Oct 2011 09:18:33 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	herbert@...dor.hengli.com.au, evonlanthen@...il.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	timo.teras@....fi
Subject: Re: PROBLEM: System call 'sendmsg' of process ospfd (quagga) causes
 kernel oops

Le mercredi 19 octobre 2011 à 03:09 -0400, David Miller a écrit :
> From: Herbert Xu <herbert@...dor.hengli.com.au>
> Date: Tue, 18 Oct 2011 15:45:37 +0200
> 
> > On Tue, Oct 18, 2011 at 02:56:00PM +0200, Eric Dumazet wrote:
> >>
> >> I am ok by this way, but we might hit another similar problem elsewhere.
> >> 
> >> (igmp.c ip6_output, ...)
> >> 
> >> We effectively want to remove LL_ALLOCATED_SPACE() usage and obfuscate
> >> code...
> > 
> > Here's another idea, provide a helper to do the skb allocation
> > and the skb_reserve in one go.  That way this ugliness would only
> > need to be done once.
> 
> Someone please test this:
> 
> --------------------
> net: Fix crashes on devices which dynamically change needed headroom.
> 
> One such device is IP_GRE.
> 
> The problem is that we evaluate the device characteristics twice, once
> to determine the allocation size, and once to do the skb_reserve().
> 
> Combine these into one operation using a helper function.
> 
> With help from Eric Dumazet and Herbert Xu.
> 
> Reported-by: Reported-by: Elmar Vonlanthen <evonlanthen@...il.com>
> Signed-off-by: David S. Miller <davem@...emloft.net>
> 



Seems fine (Maybe do the +15 in caller site ?), but we also have other
problematic cases, using alloc_skb() only...



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