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

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Message-ID: <CABe5r8JJPuhq3r=JnfLA=_U46-SFmK+g3XqC3MaRdLxwVXx9Qw@mail.gmail.com>
Date:	Thu, 12 Apr 2012 23:31:47 +0200
From:	Eldad Zack <eldad@...refinery.com>
To:	David Miller <davem@...emloft.net>
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

On 12 April 2012 22:00, David Miller <davem@...emloft.net> wrote:
>> 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.
> 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.

That's the way I see it, as was my initial intent. Then I got
concerned with the possibility that a communication with
slightly-broken stack implementation (e.g., unsanitized buffers) would
fail without the user being able to control it at runtime.
Do you consider this a non-issue?

If not, please apply the (soon to be sent) patch.

Thanks,
Eldad
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