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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: ebiederm@xmission.com (Eric W. Biederman)
Subject: Re: [PATCH] exit: PR_SET_ANCHOR for marking processes as reapers for child processes
Cc: kosaki.motohiro@jp.fujitsu.com, Lennart Poettering <mzxreary@0pointer.de>,
       Oleg Nesterov <oleg@redhat.com>, linux-kernel@vger.kernel.org,
       Americo Wang <xiyou.wangcong@gmail.com>,
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       Michael Kerrisk <mtk.manpages@googlemail.com>,
       Roland McGrath <roland@redhat.com>
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Date: Thu, 11 Mar 2010 16:56:45 +0900 (JST)
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> Lennart Poettering <mzxreary@0pointer.de> writes:
> 
> > On Thu, 04.03.10 15:08, Oleg Nesterov (oleg@redhat.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.

I guess it doesn't fit for gnome-session. because gtop or similar
system monitoring process assume it can see all processes in the system.

thanks.