linux-kernel - Re: [PATCH] netfilter: use krealloc() in nf_conntrack

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Message-ID: <4857C2B8.8070004@trash.net>
Date:	Tue, 17 Jun 2008 15:57:12 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Pekka Enberg <penberg@...helsinki.fi>
CC:	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, mpm@...enic.com, clameter@....com
Subject: Re: [PATCH] netfilter: use krealloc() in nf_conntrack_extend.c V2

Pekka Enberg wrote:
> Patrick McHardy wrote:
>> Great, thanks for the explanation. Is this patch targeted
>> at 2.6.26 or 2.6.27?
> 
> I don't think we will be removing ksize() in 2.6.26 anyway so 2.6.27 is 
> fine for this patch. Thanks!

Your patch introduced a use-after-free and double-free.
krealloc() frees the old pointer, but it is still used
for the ->move operations, then freed again.

To fix this I think we need a __krealloc() that doesn't
free the old memory, especially since it must not be
freed immediately because it may still be used in a RCU
read side (see the last part in the patch attached to
this mail (based on a kernel without your patch)).

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