linux-kernel - Re: [PATCH] [RFC] mnt: add ability to clone mntns starting with the current root

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Date:	Tue, 7 Oct 2014 14:30:40 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Andrey Vagin <avagin@...nvz.org>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org, Andrey Vagin <avagin@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Rob Landley <rob@...dley.net>
Subject: Re: [PATCH] [RFC] mnt: add ability to clone mntns starting with the
 current root

On Tue, Oct 07, 2014 at 04:12:57PM +0400, Andrey Vagin wrote:
> Another problem is that rootfs can't be hidden from a container, because
> rootfs can't be moved or umounted.

... which is a bug in mntns_install(), AFAICS.

> Here is an example how to get access to rootfs:
> fd = open("/proc/self/ns/mnt", O_RDONLY)
> umount2("/", MNT_DETACH);
> setns(fd, CLONE_NEWNS)
> 
> rootfs may contain data, which should not be avaliable in CT-s.

Indeed.

> I suggest to add ability to create a mount namespace with specified
> mount points. A current task root can be used as a root for the new
> mount namespace.

Yecchh...  Frankly, you are opening a big can of worms - having rootfs
as absolute root of all namespaces simplifies a lot of things in there.
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