Subject: Re: [regression] nf_iterate(), BUG: unable to handle kernel NULL
	pointer dereference
From: Pekka Enberg <penberg@cs.helsinki.fi>
To: Patrick McHardy <kaber@trash.net>
Cc: 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, akpm@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>
In-Reply-To: <48888434.3030207@trash.net>
References: <20080724060448.GA10203@elte.hu>
	 <E1KLwlD-0001Ub-00@gondolin.me.apana.org.au>
	 <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>
	 <48888434.3030207@trash.net>
Date: Thu, 24 Jul 2008 16:34:36 +0300
Message-Id: <1216906476.12021.4.camel@penberg-laptop>
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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@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?

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