linux-kernel - Re: [PATCH] userns: Allow the unprivileged users to mount mqueue fs

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Message-ID: <877gmxye1j.fsf@xmission.com>
Date:	Sun, 27 Jan 2013 23:14:48 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Gao feng <gaofeng@...fujitsu.com>
Cc:	serge.hallyn@...onical.com, akpm@...ux-foundation.org,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] userns: Allow the unprivileged users to mount mqueue fs

Gao feng <gaofeng@...fujitsu.com> writes:

> On 2013/01/28 11:43, Eric W. Biederman wrote:
>> Gao feng <gaofeng@...fujitsu.com> writes:
>> 
>>> This patch allow the unprivileged user to mount mqueuefs in
>>> user ns.
>>>
>>> If two userns share the same ipcns,the files in mqueue fs
>>> should be seen in both these two userns.
>>>
>>> If the userns has its own ipcns,it has its own mqueue fs too.
>>> ipcns has already done this job well.
>> 
>> I am a little dense.  When does userspace actually mount a mqueuefs?
>> My impression was that user space never needed to mount and actually
>> never could mount a mqueuefs.  MS_NO_USER isn't set so mounting a
>> mqueuefs is possible but when does it happen and why?
>> 
>
> Actually the files which representative messgae queue in mqueuefs contains
> some informations,such as QSIZE,NOTIFY,SIGNO,NOTIFY_PID.
>
> My workstation is Fedora 17,mqueuefs is mounted on /dev/mqueue by default.
> So I think at lest this patch is needed by some people.

I have just confirmed that the most you can do in a mounted mqueue fs is
to create files message queues.

Given that these filesystems exist anyway I don't see a problem.

Applied thanks.

Eric
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