Date: Thu, 24 Jul 2008 11:51:27 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Patrick McHardy <kaber@trash.net>, Ingo Molnar <mingo@elte.hu>,
       David Miller <davem@davemloft.net>, herbert@gondor.apana.org.au,
       w@1wt.eu, davidn@davidnewall.com, torvalds@linux-foundation.org,
       netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
       stefanr@s5r6.in-berlin.de, rjw@sisk.pl, ilpo.jarvinen@helsinki.fi,
       Dave Jones <davej@redhat.com>
Subject: Re: [regression] nf_iterate(), BUG: unable to handle kernel NULL
 pointer dereference
Message-Id: <20080724115127.6cfbb616.akpm@linux-foundation.org>
In-Reply-To: <1216906476.12021.4.camel@penberg-laptop>
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	<20080724.022259.113079007.davem@davemloft.net>
	<20080724093411.GA12001@elte.hu>
	<20080724115625.GA23994@elte.hu>
	<20080724115957.GA25701@elte.hu>
	<48886FA6.6050908@trash.net>
	<84144f020807240544q507e1b7cv220d1afbae0ee0f0@mail.gmail.com>
	<48887A71.5010209@trash.net>
	<1216905812.5897.6.camel@penberg-laptop>
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On Thu, 24 Jul 2008 16:34:36 +0300 Pekka Enberg <penberg@cs.helsinki.fi> wrote:

> > >> 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)).
> > > 
> > > Agreed. Something like this, perhaps?
> > > 
> > > [PATCH] netfilter: fix double-free and use-after free
> > > 
> > > As suggested by Patrick McHardy, introduce a __krealloc() that doesn't
> > > free the original buffer to fix a double-free and use-after-free bug
> > > introduced by me in netfilter that uses RCU.
> > > 
> > > Reported-by: Patrick McHardy <kaber@trash.net>
> > > Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
> > 
> > Looks good to me, thanks.
> 
> Ingo, can you please test this? Andrew, I'm at OLS so can you pick up
> the patch in your tree?

Sure.  Or Patrick can do so and it can be merged via the net tree.

Ingo, did this patch actually fix something over there?
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