linux-kernel - Re: [regression] nf_iterate(), BUG: unable to handle kernel NULL pointer dereference

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Message-Id: <20080724115127.6cfbb616.akpm@linux-foundation.org>
Date:	Thu, 24 Jul 2008 11:51:27 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Patrick McHardy <kaber@...sh.net>, Ingo Molnar <mingo@...e.hu>,
	David Miller <davem@...emloft.net>,
	herbert@...dor.apana.org.au, w@....eu, davidn@...idnewall.com,
	torvalds@...ux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, stefanr@...6.in-berlin.de,
	rjw@...k.pl, ilpo.jarvinen@...sinki.fi,
	Dave Jones <davej@...hat.com>
Subject: Re: [regression] nf_iterate(), BUG: unable to handle kernel NULL
 pointer dereference

On Thu, 24 Jul 2008 16:34:36 +0300 Pekka Enberg <penberg@...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@...sh.net>
> > > Signed-off-by: Pekka Enberg <penberg@...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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