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

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Message-Id: <1216906476.12021.4.camel@penberg-laptop>
Date:	Thu, 24 Jul 2008 16:34:36 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Ingo Molnar <mingo@...e.hu>, David Miller <davem@...emloft.net>,
	herbert@...dor.apana.org.au, w@....eu, davidn@...idnewall.com,
	torvalds@...ux-foundation.org, akpm@...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, 2008-07-24 at 15:31 +0200, Patrick McHardy wrote:
> Pekka Enberg wrote:
> > On Thu, 2008-07-24 at 14:49 +0200, Patrick McHardy wrote:
> >> Pekka Enberg wrote:
> >>> Hmm, why do you think it's related? It looks like elem->hook() is a
> >>> NULL pointer but my patch shouldn't make any difference here...
> >> No, its already in ipv4_confirm, so its most likely helper->help()
> >> thats NULL, which is contained in an extension.
> >>
> >> The reason why I think its this patch is (quoting from an old
> >> email that I never got a response to):
> > 
> > Oh, I'm really sorry about that.
> 
> No problem :)
> 
> >> ---
> >> 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?

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