[RFC][PATCH] Disable CLONE_PARENT for init

[Oleg Nesterov]

On 07/02, Oleg Nesterov wrote:
>
> On 07/01, Sukadev Bhattiprolu wrote:
> >
> > --- linux-mmotm.orig/kernel/fork.c	2009-06-30 23:01:06.000000000 -0700
> > +++ linux-mmotm/kernel/fork.c	2009-07-01 17:29:09.000000000 -0700
> > @@ -974,6 +974,16 @@ static struct task_struct *copy_process(
> >  	if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
> >  		return ERR_PTR(-EINVAL);
> >
> > +	/*
> > +	 * Siblings of global init remain as zombies on exit since they are
> > +	 * not reaped by their parent (swapper). To solve this and to avoid
> > +	 * multi-rooted process trees, prevent global and container-inits
> > +	 * from creating siblings.
> > +	 */
> > +	if ((clone_flags & CLONE_PARENT) &&
> > +				current->signal->flags & SIGNAL_UNKILLABLE)
> > +		return ERR_PTR(-EINVAL);
>
> Acked-by: Oleg Nesterov <oleg at redhat.com>

Thinking more, perhaps it makes sense to disallow CLONE_VM too.

If init forks CLONE_VM task, this task can be killed by
sig_kernel_coredump signal. In that case init will be killed too
and the kernel will crash.

But this is minor, we can trust the global init.

Oleg.