linux-kernel - Re: [PATCH][BUGFIX] cgroups: fix pid namespace bug

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Message-ID: <20090702163731.GA14267@us.ibm.com>
Date:	Thu, 2 Jul 2009 11:37:31 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Paul Menage <menage@...gle.com>
Cc:	Li Zefan <lizf@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH][BUGFIX] cgroups: fix pid namespace bug

Quoting Paul Menage (menage@...gle.com):
> On Wed, Jul 1, 2009 at 6:24 PM, Li Zefan<lizf@...fujitsu.com> wrote:
> > +       cp = kzalloc(sizeof(*cp), GFP_KERNEL);
> > +       if (!cp) {
> > +               up_write(&cgrp->pids_mutex);
> > +               kfree(pidarray);
> > +               return -ENOMEM;
> > +       }
> > +       cp->cgrp = cgrp;
> > +       cp->pid_ns = pid_ns;
> 
> You're storing an uncounted reference to the pid ns here - there's no
> guarantee that the pid_ns will outlive the open file.

Yeah I was thinking about that, but

	1. the only way it won't outlive the open file is if the 
		task opens the file, hands the open fd over a
		unix socket, then exits as the last task of its
		pidns
	2. We don't dereference the pid_ns, so there is no actual
		safety issue.  So it would become a problem only
		if a new pidns gets created at that same address
		*and* a task in the new pidns opens the same
		tasks file.

Still, it wouldn't hurt to do get_pid_ns/put_pid_ns at the open
and release :)

-serge
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