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.