linux-kernel - Re: [RFC] mlock/stack guard interaction fixup

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Message-ID: <AANLkTinY6GcgVKznUOcxh28xS3Dvy71Ln4vS-eV8F+na@mail.gmail.com>
Date:	Mon, 23 Aug 2010 09:34:14 -0700
From:	Tony Luck <tony.luck@...el.com>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ian Campbell <ijc@...lion.org.uk>,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	stable-review@...nel.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Greg KH <gregkh@...e.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [RFC] mlock/stack guard interaction fixup

On Sat, Aug 21, 2010 at 9:08 AM, Sam Ravnborg <sam@...nborg.org> wrote:
> Tony Luck already provided a VM_GROWSUP version.
>
>    See: http://lkml.org/lkml/2010/8/20/325
>
> [It is signed off by Tony Luc - but I guess they know each other ;-) ]

Tony Luc spends too much time looking at the To: and Cc: to make
sure that he spelled *other* peoples names correctly.

That patch doesn't apply any more because of the latest change to look
at vm_prev instead of calling find_vma() [N.B. the block comment above
check_stack_guard_page() still talks about find_vma()].  I can fix up my
patch ... but I have to wonder whether the new code doesn't leave a
hole again.  It assumes that any VM_GROWSDOWN object that is
found below the current one is the result of the stack vma having been
split. But couldn't an attacker have used MAP_GROWSDOWN when
placing their sneaky stack smashing mapping just below the stack?

-Tony
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