linux-kernel - Re: [PATCH 2/2] pidns: Support unsharing the pid namespace.

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Date:	Fri, 18 Feb 2011 15:40:19 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Greg Kurz <gkurz@...ibm.com>
Cc:	Daniel Lezcano <daniel.lezcano@...e.fr>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, ebiederm@...ssion.com,
	akpm@...ux-foundation.org, xemul@...nvz.org
Subject: Re: [PATCH 2/2] pidns: Support unsharing the pid namespace.

On 02/17, Greg Kurz wrote:
>
> On 02/17/2011 09:29 PM, Oleg Nesterov wrote:
>> On 02/17, Daniel Lezcano wrote:
>>>
>>> On 02/15/2011 08:01 PM, Oleg Nesterov wrote:
>>>>
>>>> I have to admit, I can't say I like this very much. OK, if we need
>>>> this, can't we just put something into, say, signal->flags so that
>>>> copy_process can check and create the new namespace.
>>>>
>>>> Also. I remember, I already saw something like this and google found
>>>> my questions. I didn't actually read the new version, perhaps my
>>>> concerns were already answered...
>>>>
>>>> 	But what if the task T does unshare(CLONE_NEWPID) and then, say,
>>>> 	pthread_create() ? Unless I missed something, the new thread won't
>>>> 	be able to see T ?
>>>
>>> Right. Is it really a problem ? I mean it is a weird use case where we
>>> fall in a weird situation.
>>
>> But this is really weird! How it is possible that the parent can't see
>> its own child? No matter which thread did fork(), the new process is
>
> Hmmm... I guess you mean the opposite. The way pid namespaces are
> nested, parents always see their children.

Well, yes. But it can't see this child using the same pid number,
unless I missed something.

> But indeed, the child thread
> can't see its group leader and that's kind of unusual.

This too. And to me this is more "kind of buggy". But yes, I am
biased because I dislike this approach in general ;)

And, once again, this patch also lacks the necessary s/nsproxy/atcive_pid_ns/
changes.

Anyway. It is very possible I missed something. As I said, I didn't
actually read this version and I forgot all I knew about this change
before.

But afaics this patch is buggy in its current form.

Oleg.

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