From mboxrd@z Thu Jan  1 00:00:00 1970
From: Aristeu Rozanski <aris-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH] device_cgroup: fix unchecked cgroup parent usage
Date: Thu, 1 Nov 2012 09:28:38 -0400
Message-ID: <20121101132837.GE14789@redhat.com>
References: <20121031160430.GD14789@redhat.com>
 <20121031163501.79a0950e.akpm@linux-foundation.org>
Mime-Version: 1.0
Return-path: <cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Content-Disposition: inline
In-Reply-To: <20121031163501.79a0950e.akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
List-ID: <cgroups.vger.kernel.org>
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
To: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, James Morris <jmorris-gx6/JNMH7DfYtjvyW6yDsg@public.gmane.org>, Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>, Serge Hallyn <serge.hallyn-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>, Jiri Slaby <jslaby-AlSwsSmVLrQ@public.gmane.org>, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org

On Wed, Oct 31, 2012 at 04:35:01PM -0700, Andrew Morton wrote:
> On Wed, 31 Oct 2012 12:04:30 -0400
> Aristeu Rozanski <aris-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
> 
> > In 4cef7299b4786879a3e113e84084a72b24590c5b the cgroup parent usage is
> > unchecked. root will not have a parent and trying to use
> > device.{allow,deny} will cause problems.
> 
> From my reading of the code "problems" means "kernel null pointer
> dereference".

yes. you want me to resubmit it fixing it or you want to update it?

> >  static inline int may_allow_all(struct dev_cgroup *parent)
> 
> offtopic: this function could quite neatly have a bool return type.

ok, will do.

> >  {
> > +	if (!parent)
> > +		return 1;
> 
> hm.  Does it need a comment explaining what and why?  I guess not...  just.

it's because the root's parent has to always allows full access to all
devices. I can add a comment when I turn into a bool if you want.

-- 
Aristeu