Date: Wed, 15 Feb 2012 23:57:33 +0400
From: Vasiliy Kulikov <segoon@openwall.com>
To: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Oleg Nesterov <oleg@redhat.com>,
        "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>,
        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
Message-ID: <20120215195733.GA8021@albatros>
References: <20120215143606.GA14037@redhat.com>
 <20120215151008.GL1894@moon>
 <20120215153816.GA15988@redhat.com>
 <20120215161329.GM1894@moon>
 <20120215162222.GA18266@redhat.com>
 <20120215175319.GG4533@moon>
 <20120215184336.GA24182@redhat.com>
 <20120215195610.GJ4533@moon>
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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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