Re: [PATCH 3/3] fork: unify and tighten up CLONE_NEWUSER/CLONE_NEWPID checks

[Oleg Nesterov <oleg@redhat.com>]

On 08/22, Andy Lutomirski wrote:
>
> On Thu, Aug 22, 2013 at 10:10 AM, Oleg Nesterov <oleg@redhat.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.