linux-kernel - Re: [patch] cgroups: disallow attaching kthreadd

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Date:	Wed, 04 Apr 2012 04:34:38 +0200
From:	Mike Galbraith <mgalbraith@...e.de>
To:	Tejun Heo <tj@...nel.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Li Zefan <lizf@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Paul Menage <paul@...lmenage.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch] cgroups: disallow attaching kthreadd

On Tue, 2012-04-03 at 11:49 -0700, Tejun Heo wrote: 
> On Tue, Apr 03, 2012 at 07:58:26PM +0200, Mike Galbraith wrote:
> > @@ -1894,6 +1895,14 @@ int cgroup_attach_task(struct cgroup *cg
> >  	if (tsk->flags & PF_EXITING)
> >  		return -ESRCH;
> >  
> > +	/*
> > +	 * Workqueue threads may acquire PF_THREAD_BOUND and become
> > +	 * trapped in a cpuset, or RT worker may be born in a cgroup
> > +	 * with no rt_runtime allocated.  Just say no.
> > +	 */
> > +	if (tsk == kthreadd_task)
> > +		return -EINVAL;
> > +
> >  	/* Nothing to do if the task is already in that cgroup */
> >  	oldcgrp = task_cgroup_from_root(tsk, root);
> >  	if (cgrp == oldcgrp)
> > @@ -2172,6 +2181,17 @@ static int attach_task_by_pid(struct cgr
> >  
> >  	if (threadgroup)
> >  		tsk = tsk->group_leader;
> > +
> > +	/*
> > +	 * Workqueue threads may acquire PF_THREAD_BOUND and become
> > +	 * trapped in a cpuset, or RT worker may be born in a cgroup
> > +	 * with no rt_runtime allocated.  Just say no.
> > +	 */
> > +	if (tsk == kthreadd_task) {
> > +		ret = -EINVAL;
> > +		goto out_unlock_cgroup;
> > +	}
> 
> If we have this test here, do we need the same check in
> cgroup_attach_task()/

It looked to me like yes, because cgroup_attach_task() can be called
directly.  For the problem at hand, user script doing bad things, no,
it's not needed.

-Mike

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