linux-kernel - Re: [PATCH 2/2] ns: Add proc_ns_operations for mount namespaces

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Date:	Sat, 12 May 2012 15:42:42 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Daniel Lezcano <dlezcano@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/2] ns: Add proc_ns_operations for mount namespaces

On 05/11/2012 09:05 PM, Eric W. Biederman wrote:
> Pavel Emelyanov <xemul@...allels.com> writes:
> 
>> Currently LXC by default creates a container in a new mount
>> namespace. Thus in order to explore it we have to
>>
>> a) find out, that a new mount namespace is in use
>> b) enter this other namespace
>>
>> This patch solves both -- allows us to distinguish one mount
>> namespace from another by comparing its inode numbers and lets
>> us enter a mount namespace with the setns system call.
> 
> There are two significant bugs with your patch.
> 
> You do not set fs->root or fs->pwd to values in the new mount namespace,
> I don't believe there is anywhere else in the vfs where this is possible
> except possible fchdir.
> 
> It is easily possible to create a reference counting cycle by bind
> mounting the current mount namespace into itself.
> 
> Not that I am opposed to the concept I have just been dusting my patch
> for this same functionality off.

Oh, that's just perfect. Let's move your one then. Hopefully it won't
get covered with dust again.

> Eric
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