linux-kernel - self_exec_id/parent_exec_id && CLONE

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Message-ID: <20120311174953.GB2729@redhat.com>
Date:	Sun, 11 Mar 2012 18:49:53 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Djalal Harouni <tixxdz@...ndz.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Kees Cook <keescook@...omium.org>,
	Solar Designer <solar@...nwall.com>,
	WANG Cong <xiyou.wangcong@...il.com>,
	James Morris <james.l.morris@...cle.com>,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Greg KH <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...e.hu>, Stephen Wilson <wilsons@...rt.ca>,
	"Jason A. Donenfeld" <Jason@...c4.com>
Subject: self_exec_id/parent_exec_id && CLONE_PARENT

(change subject)

On 03/11, Oleg Nesterov wrote:
>
> Well, I don't think it is right to add this counter into task_struct.
>
> It should be per-process, signal_struct makes more sense. Or may be
> mm_struct.
>
> Btw this is also true for parent_exec_id/self_exec_id, but this is
> another story.

In fact I think it would be nice to kill parent_exec_id/self_exec_id.

Afaics, this only problem is clone(CLONE_PARENT | SIGXXX). I expect
the answer is "no, can break existing applications", but I'll ask
anyway.

Can't we change this? IOW, can't we modify copy_process

	- p->exit_signal = (clone_flags & CLONE_THREAD) ? -1 : (clone_flags & CSIGNAL);
	+ p->exit_signal =
	+	(clone_flags & CLONE_THREAD) ? -1 :
	+	(clobe_flags & CLONE_PARENT) ? current->group_leader->exit_signal :
	+	(clone_flags & CSIGNAL);

(or simply use SIGCHLD instead of group_leader->exit_signal).

Then we can kill parent_exec_id/self_exec_id if me modify de_thread()
to set ->exit_signal = SIGCHLD for every child.

I am also asking because the change above looks like the fix to me.
The child must not control its ->exit_signal, it is the parent who
decides which signal the child should use for notification.

And to me, clone(CLONE_PARENT | SIGXXX) looks like a violation of
rule above.

Oleg.

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