linux-kernel - Re: [patch 1/2] c/r: prctl: Add ability to set new mm_struct::exe

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Message-ID: <20120319231709.GM19594@moon>
Date:	Tue, 20 Mar 2012 03:17:09 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	richard -rw- weinberger <richard.weinberger@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>,
	Matt Helsley <matthltc@...ibm.com>
Subject: Re: [patch 1/2] c/r: prctl: Add ability to set new
 mm_struct::exe_file

On Tue, Mar 20, 2012 at 12:02:44AM +0100, richard -rw- weinberger wrote:
> On Mon, Mar 19, 2012 at 11:46 PM, Andrew Morton
> <akpm@...ux-foundation.org> wrote:
> > Well, let's discuss this more completely.  In what ways could an
> > attacker use this?  How serious is the problem?  What actions can be
> > taken to lessen it?  etcetera.
> 
> After considering the problem a bit more I think it's not a big problem.
> We must not trust /proc/pid/exe in anyway.

Well, Richard, we probably do not trust it anyway but sysadmins might do
(and this was another reason for one-shot behaviour -- to not bring
 heart attacks to sysadmins, and everyone would know this link might
 be changed only one time ;)

> An attacker can always execute another binary without calling execve().

That's what c/r basically does :)

> 
> So, why makes that one-short fashion the feature more secure?
> Let the user change the exe symlink as often as he wants.
> From a security point of view the exe symlink is anyway useless.

Maybe better to call it 'predictable' then rather than 'secure'?

	Cyrill
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