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

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Date:	Sun, 27 Jan 2013 19:43:25 -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:

> 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?

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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