linux-kernel - Re: [PATCH] net/ipv6/exthdrs.c et al: Optional strict PadN option checking

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Date:	Thu, 12 Apr 2012 16:00:40 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eldad@...refinery.com
Cc:	kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	kaber@...sh.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net/ipv6/exthdrs.c et al: Optional strict PadN option
 checking

From: Eldad Zack <eldad@...refinery.com>
Date: Sat,  7 Apr 2012 17:16:14 +0200

> Added strict checking of PadN. PadN can be used to increase header
> size and thus push the protocol header into the 2nd fragment.
> 
> PadN is used to align the options within the Hop-by-Hop or
> Destination Options header to 64-bit boundaries. The maximum valid
> size is thus 7 bytes.
> RFC 4942 recommends to actively check the "payload" itself and
> ensure that it contains only zeroes.
> 
> See also RFC 4942 section 2.1.9.5.
> 
> Signed-off-by: Eldad Zack <eldad@...refinery.com>

I think you should do away with the sysctl and always perform these
checks.

At the very leat, the optlen > 7 check should always be performed.
And frankly the pad byte being zero check makes sense to do all the
time as far as I can tell too.
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