netdev - Re: [PATCH] Prevent reading uninitialized memory with socketfilters

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Date:	Wed, 10 Nov 2010 19:33:44 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	drosenberg@...curity.com, netdev@...r.kernel.org,
	stable@...nel.org, security@...nel.org
Subject: Re: [PATCH] Prevent reading uninitialized memory with socketfilters

Le mercredi 10 novembre 2010 à 10:21 -0800, David Miller a écrit :
> From: "Dan Rosenberg" <drosenberg@...curity.com>
> Date: Wed, 10 Nov 2010 18:18:08 +0000
> 
> > The code sample I linked to clearly demonstrates exactly how to
> > accomplish this, if you had bothered to read it.
> 
> I told you why I didn't read it, if you had bothered to read my
> reply properly :-)
> 
> Anyways, I realize we have to do something, but memset() is going
> to completely kill performance.  I consider Eric's suggestion the
> closest to acceptable cost at this point but even that is hard
> to digest for me.


Most filters dont use mem[] at all, so the added cost seems OK to me,
but we can work to use a compile time check, to make memset(mem, 0,
length) a filter parameter if you prefer removing the test on each
load(mem[K]).

This memset() could be avoided if the compiler() can be sure all
load(mem[K]) follow a prior store(mem[K])

Its not a five minutes patch, I tried to work on it but it was a bit
hard, for a very remote security risk.

(On x86 platform, incoming packets are handled in SOFTIRQ stack, not the
kernel stack of current thread anyway)



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