netdev - Re: [PATCH] netfilter: xtables: fix reentrancy

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Date:	Thu, 17 Mar 2011 12:36:56 +0100 (CET)
From:	Jesper Dangaard Brouer <hawk@...u.dk>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Patrick McHardy <kaber@...sh.net>,
	Netfilter Developers <netfilter-devel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] netfilter: xtables: fix reentrancy


Hi Eric,

How critial is this bug fix?

Should I apply this on my stable production kernels?
(I'm preparing a 2.6.38 kernel for prod usage, eventhougt its just been 
released, because I want your SFQ fixes...)


On Thu, 17 Mar 2011, Eric Dumazet wrote:

> While looking at it (and trying to only require preemption disabled
> instead of BH disabled), I believe stackptr management is not safe.
>
> I suggest following patch to make sure we restore *stackptr to origptr
> before enabling BH (or preemption later)
>
> Thanks
>
> [PATCH] netfilter: xtables: fix reentrancy
>
> commit f3c5c1bfd4308 (make ip_tables reentrant) introduced a race in
> handling the stackptr restore, at the end of ipt_do_table()
>
> We should do it before the call to xt_info_rdunlock_bh(), or we allow
> cpu preemption and another cpu overwrites stackptr of original one.
>
> A second fix is to change the underflow test to check the origptr value
> instead of 0 to detect underflow, or else we allow a jump from different
> hooks.
>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
[...]

Hilsen
   Jesper Brouer

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