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

From: Cyrill Gorcunov <gorcunov@openvz.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
	Pavel Emelyanov <xemul@parallels.com>,
	Andrey Vagin <avagin@openvz.org>,
	KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
	Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Glauber Costa <glommer@parallels.com>,
	Andi Kleen <andi@firstfloor.org>, Tejun Heo <tj@kernel.org>,
	Matt Helsley <matthltc@us.ibm.com>,
	Pekka Enberg <penberg@kernel.org>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	Vasiliy Kulikov <segoon@openwall.com>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Valdis.Kletnieks@vt.edu, Michal Marek <mmarek@suse.cz>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org
Subject: Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree
Date: Wed, 15 Feb 2012 23:56:10 +0400	[thread overview]
Message-ID: <20120215195610.GJ4533@moon> (raw)
In-Reply-To: <20120215184336.GA24182@redhat.com>

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