linux-kernel - Re: [RFC][PATCH 2/2] Prevent container-inits from using CLONE

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Message-ID: <20090618154216.GB6404@redhat.com>
Date:	Thu, 18 Jun 2009 17:42:16 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	serue@...ibm.com, "Eric W. Biederman" <ebiederm@...ssion.com>,
	roland@...hat.com, Pavel Emelyanov <xemul@...nvz.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Oren Laadan <orenl@...columbia.edu>,
	"David C. Hansen" <haveblue@...ibm.com>,
	Containers <containers@...ts.linux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 2/2] Prevent container-inits from using
	CLONE_PARENT

On 06/18, Oleg Nesterov wrote:
>
> On 06/17, Sukadev Bhattiprolu wrote:
> >
> > @@ -974,6 +974,14 @@ static struct task_struct *copy_process(
> >  	if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
> >  		return ERR_PTR(-EINVAL);
> >
> > +	/*
> > +	 * To keep pid namespace semantics simple, prevent container-inits
> > +	 * from creating siblings.
> > +	 */
> > +	if ((clone_flags & CLONE_PARENT) &&
> > +			is_container_init(current) && !is_global_init(current))
>
> Both is_ checks are not right afaics. There are per-thread. This means
> that container-init can do clone(CLONE_THREAD), and then this thread
> does CLONE_PARENT and fools copy_process().
>
> As for !is_global_init(). I never understood what should we do if the
> global init does CLONE_PARENT, this attaches another process to swapper,
> not good.

Hmm. And idle threads run with ->action[SIGHLD] == SIG_DFL, so this is
really wrong. Fortunately, we can trust the global init.

Oleg.

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