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

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Message-ID: <20120215195733.GA8021@albatros>
Date:	Wed, 15 Feb 2012 23:57:33 +0400
From:	Vasiliy Kulikov <segoon@...nwall.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	"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>,
	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 23:56 +0400, Cyrill Gorcunov wrote:
> 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...

Look at fs/proc/base.c:lock_trace() - it locks ->cred_guard_mutex
for the whole period of time when it uses a resource.

-- 
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments
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