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

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Date:	Mon, 19 Aug 2013 11:40:31 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Oleg Nesterov <oleg@...hat.com>
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 Mon, Aug 19, 2013 at 11:33 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> 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) ?

I think that removing the CLONE_VM check is fine (although there are
some other ones that should probably be removed as well), but I'm not
sure if that check needs replacing with something else.

--Andy
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