linux-kernel - Re: [PATCH c/r -mm] c/r: prctl: Simplify PR_SET

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Date:	Tue, 17 Apr 2012 12:53:17 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH c/r -mm] c/r: prctl: Simplify PR_SET_MM on mm::code/data assignment

On Tue, Apr 17, 2012 at 12:49 PM, Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
> On Tue, Apr 17, 2012 at 11:19:16PM +0400, Cyrill Gorcunov wrote:
> ...
>> > Since this is CAP_SYS_RESOURCE, and mmap_min_addr is CAP_SYS_RAWIO,
>> > how about a lower-bounds check against mmap_min_addr? (We're already
>> > doing the TASK_SIZE upper check, so this additional sanity checking
>> > seems reasonable to me.)
>>
>> I think this is good idea, thanks Kees. I'll check it out.
>
> Updated and tested version is below.
>
>        Cyrill
> ---
> From: Cyrill Gorcunov <gorcunov@...nvz.org>
> Subject: [PATCH] c/r: prctl: Simplify PR_SET_MM on mm::code/data assignment v2
>
> The mm::start_code, end_code, start_data, end_data members
> are set during startup of executable file and are not changed
> after.
>
> But the program itself might map new executable or/and data areas in
> time so the original values written into mm fields mentioned above
> might not have correspond VMA area at all, thus if one try to
> use this prctl codes without underlied VMA, the error will be
> returned.
>
> Drop this requirement. This shrinks the code and eliminates
> redundant calls to vma_flags_mismatch. The worst thing one can
> do (if say to write some bad values here) -- the weird results
> will be shown in /proc/$pid/statm or in /proc/pid/stat.
>
> Still, assignement of data on stack (such as command line and
> environment variables) requires the underlied VMA to exist.
>
> v2:
>  Also make sure the address being set is greater than mmap_min_addr.
>  Suggested by Kees Cook.
>
> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>

Acked-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook
ChromeOS Security
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