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

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Message-ID: <51061F2F.6040104@cn.fujitsu.com>
Date:	Mon, 28 Jan 2013 14:48:15 +0800
From:	Gao feng <gaofeng@...fujitsu.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.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

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.

Thanks!
Gao

> I am trying to think through the logic here and I think this is safe
> but since I don't understand why we would mount an mqueue fs I am
> having trouble verifying that there are no silly reasons why this might
> be a bad idea.
> 
> But from what I can tell so far this seems like a good patch.
> 
> Eric
> 
> 
>> Signed-off-by: Gao feng <gaofeng@...fujitsu.com>
>> ---
>>  ipc/mqueue.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/ipc/mqueue.c b/ipc/mqueue.c
>> index 71a3ca1..023c986 100644
>> --- a/ipc/mqueue.c
>> +++ b/ipc/mqueue.c
>> @@ -1383,6 +1383,7 @@ static struct file_system_type mqueue_fs_type = {
>>  	.name = "mqueue",
>>  	.mount = mqueue_mount,
>>  	.kill_sb = kill_litter_super,
>> +	.fs_flags = FS_USERNS_MOUNT,
>>  };
>>  
>>  int mq_init_ns(struct ipc_namespace *ns)
> --
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