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

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Message-ID: <20130820190529.GA24512@redhat.com>
Date:	Tue, 20 Aug 2013 21:05:29 +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 08/20, Andy Lutomirski wrote:
>
> On Tue, Aug 20, 2013 at 11:50 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> >> Currently (with or without your patch), vfork() followed by
> >> unshare(CLONE_NEWUSER) or unshare(CLONE_NEWPID) will unshare the VM.
> >
> > Could you spell please?
> >
> > We never unshare the VM. CLONE_VM in sys_unshare() paths just means
> > "fail unless ->mm is not shared".
> >
>
> Argh.  In that case this is probably buggy,

I don't think so. Just we can't really unshare ->mm or implement
unshare(CLONE_THREAD). We simply pretend it works if there is nothing
to unshare.

> sys_unshare will see CLONE_NEWPID or CLONE_NEWUSER and set
> CLONE_THREAD.  Then it will see CLONE_THREAD and set CLONE_VM.

This matches copy_process() to some degree... but looks confusing,
I agree.

> Could this be made much more comprehensible by having a single list of
> shareable things are allowed to be shared across namespaces and
> enforcing the *same* list in clone and unshare?

Not sure...

but at least we can probably simplify this a little bit. Say, we can
just kill

	if (unshare_flags & CLONE_THREAD)
		unshare_flags |= CLONE_VM;

Oleg.

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