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

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Date:	Fri, 27 Sep 2013 12:03:12 -0700
From:	Kees Cook <kees@...flux.net>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	Andi Kleen <ak@...ux.intel.com>, Wolfram Gloger <wg@...loc.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Kostya Serebryany <kcc@...gle.com>, x86@...nel.org
Subject: Re: Out-of-bounds access in get_wchan (arch/x86/kernel/process_64.c)

On Wed, Sep 11, 2013 at 10:16:32PM +0400, Dmitry Vyukov wrote:
> On Wed, Sep 11, 2013 at 2:06 AM, Andi Kleen <ak@...ux.intel.com> wrote:
> >> Indeed, get_wchan ensures that fp<stack+THREAD_SIZE, but then dereferences fp+8:
> >>
> >> 434                 if (fp < (unsigned long)stack ||
> >> 435                     fp >= (unsigned long)stack+THREAD_SIZE)
> >> 436                         return 0;
> >> 437                 ip = *(u64 *)(fp+8);
> >>
> >> It must check that fp+8<stack+THREAD_SIZE.
> >> As far as I see, the bug can lead to garbage return values or in the
> >> worst case to crash.
> >
> > Thanks for the report.
> >
> > The change looks good to me. Can you please submit a formal signed off patch
> > to x86@...nel.org ?

Can you CC this to lkml as well? x86@ isn't a public list, IIUC.

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.

-Kees

-- 
Kees Cook                                            @outflux.net
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