linux-kernel - Re: [RFC][v8][PATCH 3/10]: Make pid_max a pid

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Message-ID: <20091013152453.GA9994@us.ibm.com>
Date:	Tue, 13 Oct 2009 10:24:53 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Pavel Emelyanov <xemul@...nvz.org>
Cc:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, Oren Laadan <orenl@...columbia.edu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...l.org>, torvalds@...ux-foundation.org,
	mikew@...gle.com, mingo@...e.hu, hpa@...or.com,
	Nathan Lynch <nathanl@...tin.ibm.com>, arnd@...db.de,
	peterz@...radead.org, Louis.Rilling@...labs.com, roland@...hat.com,
	kosaki.motohiro@...fujitsu.com, randy.dunlap@...cle.com,
	linux-api@...r.kernel.org,
	Containers <containers@...ts.linux-foundation.org>,
	sukadev@...ibm.com
Subject: Re: [RFC][v8][PATCH 3/10]: Make pid_max a pid_ns property

Quoting Pavel Emelyanov (xemul@...nvz.org):
> Sukadev Bhattiprolu wrote:
> > 
> > From: Serge Hallyn <serue@...ibm.com>
> > Subject: [RFC][v8][PATCH 3/10]: Make pid_max a pid_ns property
> > 
> > Remove the pid_max global, and make it a property of the
> > pid_namespace.  When a pid_ns is created, it inherits
> > the parent's pid_ns.
> > 
> > Fixing up sysctl (trivial akin to ipc version, but
> > potentially tedious to get right for all CONFIG*
> > combinations) is left for later.
> > 
> > Changelog[v2]:
> > 	- Port to newer kernel
> > 	- Make pid_max a local variable in alloc_pidmap() to simplify code/patch
> > 
> > Signed-off-by: Serge Hallyn <serue@...ibm.com>
> > Signed-off-by: Sukadev Bhattiprolu <sukadev@...ibm.com>
> 
> Not that I'm about to slow down or block the process, but...

This patch isn't a core part of the clone_with_pid functionality,
just something Eric has asked for.  So I don't object to dropping
it.  But I disagree with Alexey's claim that this isn't a namespace
property.  It should be.

> frankly I don't see the reason for doing so. Why should we?
> Especially taking into account, that we essentially cannot
> change thin in the namespace level 3 and deeper?

What do you mean by that?  With this patchset we're not, it's
true, but we trivially can - even now, userspace can simply not
give the container CAP_SYS_ADMIN or write access to the sysctl
so they can't do any more CLONE_NEWPIDS or change the sysctl.

-serge
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