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Date:	Wed, 29 Nov 2006 03:28:25 +0100
From:	Patrick McHardy <>
To:	Krzysztof Halasa <>
CC:	David Miller <>,
	lkml <>,,
	Netfilter Development Mailinglist 
Subject: Re: Broken commit: [NETFILTER]: ipt_REJECT: remove largely duplicate
 route_reverse function

Krzysztof Halasa wrote:
> Patrick McHardy <> writes:
>>It might be the case that your network device has a
>>hard_header_len > LL_MAX_HEADER, which could trigger
>>a corruption.
> Hmm... GRE tunnels add 24 bytes... I just noticed the following code in
> include/linux/netdevice.h:
> /*
>  *      Compute the worst case header length according to the protocols
>  *      used.
>  */
> #if !defined(CONFIG_NET_IPIP) && \
>     !defined(CONFIG_IPV6) && !defined(CONFIG_IPV6_MODULE)
> #else
> #define MAX_HEADER (LL_MAX_HEADER + 48)
> #endif
> I don't use AX25, Token Ring, the old IPIP tunnels nor IPv6 here, but
> I wonder if GRE tunnel (which is basically another, more compatible
> form of IPIP) need the same treatment as IPIP.

Both ipip and gre do this:

dev->hard_header_len    = LL_MAX_HEADER + sizeof(struct iphdr);

which explains it. It is a bug in the REJECT target, but I was
wondering whether you were really seeing this. It looks like
it makes sense to add GRE to the MAX_HEADER case above though.

>>Please try this patch on top of the REJECT patch (ideally after
>>verifying that the REJECT patch is really introducing the
> That was certain. The patch fixed the problem, confirmed with current
> git tree as well. Thanks for looking at it.

Thanks. Dave, please apply this patch.

[NETFILTER]: ipt_REJECT: fix memory corruption

On devices with hard_header_len > LL_MAX_HEADER ip_route_me_harder()
reallocates the skb, leading to memory corruption when using the stale
tcph pointer to update the checksum.

Signed-off-by: Patrick McHardy <>

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