netdev - Re: net/sched/act

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Message-ID: <20100709232359.GA2501@gondor.apana.org.au>
Date:	Sat, 10 Jul 2010 07:23:59 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Rodrigo Partearroyo González 
	<rpartearroyo@...entia.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Iratxo Pichel Ortiz <ipichel@...entia.com>,
	Noelia Morón <nmoron@...entia.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: net/sched/act_nat.c BUG

On Fri, Jul 09, 2010 at 05:13:40PM +0200, Eric Dumazet wrote:
> Le vendredi 09 juillet 2010 à 16:37 +0200, Rodrigo Partearroyo González
> a écrit :
> > Hi all,
> > 
> > I have been testing Stateless NAT and found that ICMP packets with length less 
> > than 20 bytes were not correctly NAT'ed. I have found a BUG that makes taking 
> > into account IP header length twice, so ICMP packets smaller than 20 bytes 
> > were being dropped.
> > 
> 
> CC netdev
> 
> > The proposed fix is:
> > 
> > Index: net/sched/act_nat.c
> > ===================================================================
> > --- net/sched/act_nat.c
> > +++ net/sched/act_nat.c
> > @@ -202,7 +202,7 @@
> >         {
> >                 struct icmphdr *icmph;
> >  
> > -               if (!pskb_may_pull(skb, ihl + sizeof(*icmph) + sizeof(*iph)))
> > +               if (!pskb_may_pull(skb, ihl + sizeof(*icmph)))
> >                         goto drop;
> >  
> >                 icmph = (void *)(skb_network_header(skb) + ihl);
> > 
> > Please, consider applying it.
> 
> Nice catch, but take a look at next lines too,
> when call to skb_clone_writable() is done, since same error is present.
> 
> 	skb_clone_writable(skb,
> 			   ihl + sizeof(*icmph) + sizeof(*iph))
> 
> Please submit a formal patch, with your "Signed-off-by: ...", as
> documented in Documentation/SubmittingPatches

No we do need the second IP header, think about it...

However, we should only drop it only if it's long enough and
pskb_may_pull fails.

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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