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SubjectRe: net/sched/act_nat.c BUG
From
From: Herbert Xu <herbert@gondor.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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