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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH] exit: PR_SET_ANCHOR for marking processes as reapers for child processes
Cc: kosaki.motohiro@jp.fujitsu.com,
       Lennart Poettering <lennart@poettering.net>,
       linux-kernel@vger.kernel.org, Americo Wang <xiyou.wangcong@gmail.com>,
       James Morris <jmorris@namei.org>, Kay Sievers <kay.sievers@vrfy.org>,
       Kyle McMartin <kyle@redhat.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Michael Kerrisk <mtk.manpages@googlemail.com>,
       Roland McGrath <roland@redhat.com>
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Date: Fri,  5 Mar 2010 13:47:08 +0900 (JST)
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> On 02/02, Lennart Poettering wrote:
> >
> > This patch adds a simple flag for each process that marks it as an
> > "anchor" process for all its children and grandchildren. If a child of
> > such an anchor dies all its children will not be reparented to init, but
> > instead to this anchor, escaping this anchor process is not possible. A
> > task with this flag set hence acts is little "sub-init".
> 
> Lennart, this patch adds a noticeable linux-only feature. I see
> your point, but imho your idea needs the "strong" acks. I cc'ed
> some heavyweights, if someone dislikes your idea he can nack it
> right now.
> 
> 
> Security. This is beyond my understanding, hopefully the cc'ed
> experts can help.
> 
> Should we clear ->child_anchor flags when the "sub-init" execs? Or,
> at least, when the task changes its credentials? Probably not, but
> dunno.
> 
> The more problematic case is when the descendant of the "sub-init"
> execs the setuid application. Should we allow the reparenting to
> !/sbin/init task in this case?
> 
> Should we clear ->pdeath_signal after reparenting to sub-init ?
> 
> Do we need the new security_operations->task_reparent() method ?
> Or, perhaps we can reuse ->task_wait() if we add the "parent"
> argument?
> 
> Something else we should think about?

I think changing reparent rule is a bit risky. instead, I propse
that exporting ANCHOR flag via /proc and ps parse it.

What do you think?