linux-kernel - Re: [PATCH] exit: PR_SET_ANCHOR for marking processes as reapers for child processes

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Message-ID: <m1wrxjcx4w.fsf@fess.ebiederm.org>
Date:	Wed, 10 Mar 2010 20:14:55 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Lennart Poettering <mzxreary@...inter.de>
Cc:	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
	Americo Wang <xiyou.wangcong@...il.com>,
	James Morris <jmorris@...ei.org>,
	Kay Sievers <kay.sievers@...y.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Kyle McMartin <kyle@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Michael Kerrisk <mtk.manpages@...glemail.com>,
	Roland McGrath <roland@...hat.com>
Subject: Re: [PATCH] exit: PR_SET_ANCHOR for marking processes as reapers for child processes

Lennart Poettering <mzxreary@...inter.de> writes:

> On Thu, 04.03.10 15:08, Oleg Nesterov (oleg@...hat.com) wrote:
>
>> Should we clear ->child_anchor flags when the "sub-init" execs? Or,
>> at least, when the task changes its credentials? Probably not, but
>> dunno.
>
> Since this flag is only useful for a very well defined type of processes
> (i.e. session managers, supervising daemons, init systems) it might make
> sense to reset it automatically when privs are dropped or we exec
> something. After all, I don't see how we'd gain any useful functionality
> when we allow this flag to continue to be set. However we would
> certainly be on the safer side when we reset it, because that way it can
> never leak it to processes that are differently privileged or do not
> expect it.
>
> So, for the sake of being on the safe side, I think we should reset the
> flag on exec()/setuid().
>
>> It is a bit strange that PR_SET_ANCHOR acts per-thread, not per
>> process.
>
> Yes, I agree, this should be per-process indeed.

Have you take a look at the pid namespace?

Except for the fact it requires privilege to create it seems to do
what you want.  It is certainly what I have been using when I want
an inescapable environment.

If nothing else I get the feeling that what you are after is
a generalization of the child_reaper feature in the pid namespace
and yet you haven't touched any of that code.

Eric
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