linux-kernel - Re: [PATCH 3/3] fork: unify and tighten up CLONE_NEWUSER/CLONE

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Message-ID: <20130822181536.GA22995@redhat.com>
Date:	Thu, 22 Aug 2013 20:15:36 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Brad Spengler <spender@...ecurity.net>,
	Colin Walters <walters@...hat.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] fork: unify and tighten up
	CLONE_NEWUSER/CLONE_NEWPID checks

On 08/22, Andy Lutomirski wrote:
>
> On Thu, Aug 22, 2013 at 10:10 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> > do_fork() denies CLONE_THREAD | CLONE_PARENT if NEWUSER | NEWPID.
> >
> > Then later copy_process() denies CLONE_SIGHAND if the new process
> > will be in a different pid namespace (task_active_pid_ns() doesn't
> > match current->nsproxy->pid_ns).
> >
> > This looks confusing and inconsistent. CLONE_NEWPID is very similar
> > to the case when ->pid_ns was already unshared, we want the same
> > restrictions so copy_process() should also nack CLONE_PARENT.
> >
> > And it would be better to deny CLONE_NEWUSER && CLONE_SIGHAND as
> > well just for consistency.
> >
> > Kill the "CLONE_NEWUSER | CLONE_NEWPID" check in do_fork() and
> > change copy_process() to the same check along with nsproxy->pid_ns
> > we already have.
>
> Did the old code actually prevent clone(CLONE_PARENT | CLONE_NEWPID)?
> The new code explicitly does, and that looks like a good thing.


Yes. Before this patch do_fork() did:

	if (clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) {
		if (clone_flags & (CLONE_THREAD|CLONE_PARENT))
			return -EINVAL;
	}

however, let me repeat, CLONE_PARENT after unshare(CLONE_NEWPID) was
allowed. With this patch CLONE_PARENT is nacked in both cases.

Oleg.

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