linux-kernel - Re: self_exec_id/parent_exec_id && CLONE

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Message-ID: <20120311183900.GA7031@redhat.com>
Date:	Sun, 11 Mar 2012 19:39:00 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	richard -rw- weinberger <richard.weinberger@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Djalal Harouni <tixxdz@...ndz.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	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: Re: self_exec_id/parent_exec_id && CLONE_PARENT

On 03/11, richard -rw- weinberger wrote:
>
> On Sun, Mar 11, 2012 at 7:02 PM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> > On Sun, Mar 11, 2012 at 10:49 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> >>
> >> 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.
> >
> > SIGXXX is for doing things like AIO with threads, but it would never
> > be used together with CLONE_PARENT, that would be odd and wrong.
> >
> > So I think we could disallow that - or at least try. See if anybody
> > notices, and if it breaks anything.
> >
>
> UserModeLinux is using CLONE_PARENT | CLONE_FILES | SIGCHLD.
> Is this a problem?

This depends on how the forking process was created, and what its
parent expects.

If it was forked with SIGCHLD as well, then no problems. Otherwise
the parent can notice the difference.

Oleg.

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