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

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Message-ID: <20120305163130.GA13744@redhat.com>
Date:	Mon, 5 Mar 2012 17:31:30 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>
Subject: Re: [RFC] c/r: prctl: Add ability to set new mm_struct::exe_file

On 03/05, Cyrill Gorcunov wrote:
>
> On Mon, Mar 05, 2012 at 04:40:29PM +0100, Oleg Nesterov wrote:
>
> > > This prctl does cheat the kernel
> >
> > Yep. Except, well, it cheats the user-space.
>
> And kernel as well, since this link is not anymore
> the same as it was, and memory read from this file
> (at execution time) will keep data irrelevant to what
> the new symlink points to (but it's exactly by design).

The kernel will never use this file for reading. It is only
used as a placeholder for ->f_path shown in proc.

User-space can be confused, yes, this is by design.

Oleg.

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