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

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Message-Id: <1216925744.12392.1.camel@penberg-laptop>
Date:	Thu, 24 Jul 2008 21:55:44 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Andrew Morton <akpm@...ux-foundation.org>
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>, clip2@....de,
	vegard.nossum@...il.com
Subject: Re: [regression] nf_iterate(), BUG: unable to handle kernel NULL
	pointer dereference

On Thu, 2008-07-24 at 11:51 -0700, Andrew Morton wrote:
> 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?

Apparently it didn't but it did fix Dieter's problem:

http://lkml.org/lkml/2008/7/24/337

Dieter, can we add a Tested-by tag from you to this patch?

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