[kernel-hardening] Re: exec_id protection from bad child exit signals (was: Re: [PATCH 0/9] proc: protect /proc/<pid>/* files across execve)

[Oleg Nesterov <oleg@redhat.com>]

On 03/11, Solar Designer wrote:
>
> Actually, the original/historical purpose of the exec_id stuff was to
> protect privileged parent processes (those having done a SUID/SGID exec)
> from non-standard child exit signals, which could be set with clone().
> I think we may want to audit the current implementation and see if it
> still fully achieves the goal or maybe not (and fix it if not).

Funny that, I noticed this message only after I sent the question about
the current exec_id stuff.

> I include below pieces of the prototype implementation from
> linux-2.2.12-ow6.tar.gz released in 1999.

Perhaps I missed something, but ignoring the "cap_raised" issues, this
all is very simple. de_thread() should simply do:

	current->exit_signal = SIGCHLD;

	read_lock(&tasklist_lock);
	list_for_each_entry(p, &current->children, sibling)
		p->exit_signal = SIGCHILD;
	read_unlock(&tasklist_lock);

The only problem is CLONE_PARENT.

Oleg.