linux-kernel - Re: Out-of-bounds access in get_wchan (arch/x86/kernel/process

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Date:	Sat, 28 Sep 2013 14:01:11 -0700
From:	Kees Cook <kees@...flux.net>
To:	Wolfram Gloger <wg@...loc.de>
Cc:	dvyukov@...gle.com, ak@...ux.intel.com,
	linux-kernel@...r.kernel.org, pjt@...gle.com,
	andreyknvl@...gle.com, kcc@...gle.com, x86@...nel.org
Subject: Re: Out-of-bounds access in get_wchan (arch/x86/kernel/process_64.c)

On Sat, Sep 28, 2013 at 09:51:14PM +0200, Wolfram Gloger wrote:
> Kees Cook <kees@...flux.net> writes:
> 
> > Please note that these bounds checks aren't correct to begin with. Since
> > a pointer is being dereferenced, the end boundry must be reduced by
> > sizeof(unsigned long) as well.
> >
> > It looks like process_32.c suffers the same problems, too.
> 
> I can't see the end boundary problem in process_32.c.  The end checks
> are properly reduced with the top_esp and top_ebp macros.
> 
> All I can see in process_32.c is that the check
> 
> 		if (bp < stack_page || bp > top_ebp+stack_page)
> 
> could be replaced by:
> 
> 		if (bp < stack_page-sizeof(unsigned long) || bp > top_ebp+stack_page)
> 
> but that is a relaxation and not an over/underrun fix.
> 
> Can you elaborate what problem you see in process_32.c?

Ah, yes, sorry, this appears to only be a problem in process_64.c. I didn't look
closely enough. I see now that top_esp and top_ebp correctly reduce the size of
THREAD_SIZE. Thanks!

-Kees

-- 
Kees Cook                                            @outflux.net
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