netdev - Re: net/sched/act

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Message-Id: <20100709.170018.189701063.davem@davemloft.net>
Date:	Fri, 09 Jul 2010 17:00:18 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	eric.dumazet@...il.com, rpartearroyo@...entia.com,
	linux-kernel@...r.kernel.org, ipichel@...entia.com,
	nmoron@...entia.com, netdev@...r.kernel.org
Subject: Re: net/sched/act_nat.c BUG

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Sat, 10 Jul 2010 07:23:59 +0800

> 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.

Ok, I've reverted until we come up with the proper fix, thanks.
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