linux-kernel - Re: PATCH? fix unshare(NEWPID) && vfork()

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Date:	Mon, 19 Aug 2013 20:33:19 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Brad Spengler <spender@...ecurity.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Colin Walters <walters@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: PATCH? fix unshare(NEWPID) && vfork()

On 08/19, Andy Lutomirski wrote:
>
> On Mon, Aug 19, 2013 at 10:25 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> > Hello.
> >
> > Colin reports that vfork() doesn't work after unshare(PIDNS). The
> > reason is trivial, copy_process() does:
> >
> >         /*
> >          * If the new process will be in a different pid namespace
> >          * don't allow the creation of threads.
> >          */
> >         if ((clone_flags & (CLONE_VM|CLONE_NEWPID)) &&
> >             (task_active_pid_ns(current) != current->nsproxy->pid_ns))
> >                 return ERR_PTR(-EINVAL);
> >
> > and CLONE_VM obviously nacks vfork(). So perhaps we can relax
> > this check to CLONE_THREAD? Or should we really nack CLONE_VM
> > by security reasons?
> >
> > OTOH. Perhaps we should also deny CLONE_PARENT in this case?
> >
> > In short. So far I am thinking about the patch below but I got
> > lost and totally confused. Will try to think more tomorrow, but
> > I would like to see the fix from someone who still understands
> > this all.
> >
> > Oleg.
>
> By way of (partial) explanation:
>
> http://marc.info/?l=linux-kernel&m=135545831607095

Thanks... too late for me to even try to read this discussion today.

and I am a bit confused,

> (tl;dr: I think that CLONE_VM is irrelevant here, but there may be
> other issues lurking around.)

So do you think this change is fine or not (ignoring the fact it needs
cleanups) ?

Oleg.

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