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

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Date:	Fri, 5 Mar 2010 10:51:47 -0800
From:	Kay Sievers <kay.sievers@...y.org>
To:	Roland McGrath <roland@...hat.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Lennart Poettering <lennart@...ttering.net>,
	linux-kernel@...r.kernel.org,
	Americo Wang <xiyou.wangcong@...il.com>,
	James Morris <jmorris@...ei.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Kyle McMartin <kyle@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Michael Kerrisk <mtk.manpages@...glemail.com>
Subject: Re: [PATCH] exit: PR_SET_ANCHOR for marking processes as reapers for 
	child processes

On Thu, Mar 4, 2010 at 14:14, Roland McGrath <roland@...hat.com> wrote:
>> Security. This is beyond my understanding, hopefully the cc'ed
>> experts can help.
>
> There are a few different aspects of behavior change to think about.
>
> 1. Who can get a SIGCHLD and wait result they weren't expecting.
> 2. Who sees some PID for getppid() when they are expecting 1.
> 3. What ps shows.
>
> When I start thinking through what might be security issues, they are
> almost all #1 questions.  There is a hairy nest of many variations of #1
> questions.  The #2 question is pretty simple, but it also could be an issue
> for security when setuid is involved (or just correctness for any
> application).
>
> My impression is that #3 is the only actual motivation for this feature.
> So perhaps we should consider an approach that leaves the rest of the
> semantics alone and only affects that.

Oh, no. Actually getting the SIGCHILD is the needed feature here. A
process who sets the ANCHOR flag is surely expected to handle these
signals. It's all about a user "init-like" process" that can do
similar things for a logged-in user what /sbin/init can to for the
system. So, it's all about 1.), and 3.) is a nice side-effect, but not
the motivation to do this.

And 2.) is just very broken behavior that should be fixed in the
application, and it can be worked around in the sub-init process if
needed.

Thanks,
Kay
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