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

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Message-ID: <20100306002009.GI28657@tango.0pointer.de>
Date:	Sat, 6 Mar 2010 01:20:09 +0100
From:	Lennart Poettering <mzxreary@...inter.de>
To:	Roland McGrath <roland@...hat.com>
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>
Subject: Re: [PATCH] exit: PR_SET_ANCHOR for marking processes as reapers
 	for child processes

On Thu, 04.03.10 14:14, Roland McGrath (roland@...hat.com) wrote:

> 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.
> 
> Lennart, am I right that this is all you are looking for?  Does it even
> matter to you that this change the PPID that ps groks today?  How about if
> it's just an entirely new kind of assocation that ps et al can learn to
> display, and not even the traditional PPID field changes?

Uh, no. Actually it's the fact that my sub-init gets the SIGCHLD, which
I am looking for. The clean ps tree is just a side-effect.

When the sub-init gets the SIGCHLD for its "grandchildren" then we can
supervise double-forking daemons, and properly handle daemons that die
due to SIGSEGV and suchlike. 

So what I am after is the SIGCHLD for the grandparents, the clean ps
tree is kinda boring.

Lennart

-- 
Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net
http://0pointer.net/lennart/           GnuPG 0x1A015CC4
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