linux-kernel - Re: [PATCH] device_cgroup: fix unchecked cgroup parent usage

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Message-ID: <20121101132837.GE14789@redhat.com>
Date:	Thu, 1 Nov 2012 09:28:38 -0400
From:	Aristeu Rozanski <aris@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Li Zefan <lizefan@...wei.com>,
	James Morris <jmorris@...ei.org>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Jiri Slaby <jslaby@...e.cz>, cgroups@...r.kernel.org
Subject: Re: [PATCH] device_cgroup: fix unchecked cgroup parent usage

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@...hat.com> 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

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