linux-kernel - Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree

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Message-ID: <20120215195610.GJ4533@moon>
Date:	Wed, 15 Feb 2012 23:56:10 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Andrey Vagin <avagin@...nvz.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Glauber Costa <glommer@...allels.com>,
	Andi Kleen <andi@...stfloor.org>, Tejun Heo <tj@...nel.org>,
	Matt Helsley <matthltc@...ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Alexey Dobriyan <adobriyan@...il.com>, Valdis.Kletnieks@...edu,
	Michal Marek <mmarek@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree

On Wed, Feb 15, 2012 at 07:43:36PM +0100, Oleg Nesterov wrote:
...
> 
> Cough... this is question I am trying to ask ;)
> 
> Let me try again. To simplify, lets discuss the KCMP_VM case
> only.
> 
> I do not really understand why do we need ptrace_may_access().
> I do not see any security problems with kcmp_ptr(task->mm), but
> I am not expert.
> 
> However, you added this check so I assume you have some reason.
> But this can race with execve(setuid_app) and KCMP_VM can play
> with task->mm after this task raises its caps. If this is fine,
> then why do we need ptrace_may_access?
> 

This makes me scratch the head ;) I think ptrace_may_access (or
some other security test) should remain since it's somehow weird
if non-root task will be able to find objects order from privileged
task. Thus I need to find a way how to handle execve(setuid_app).
Need to think...

	Cyrill
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