hooks_ct: mount /proc and /sys before umounting old root

Here is workaround for the kernel commit:

 commit e51db73532955dc5eaba4235e62b74b460709d5b
 Author: Eric W. Biederman <ebiederm@xmission.com>
 Date:   Sat Mar 30 19:57:41 2013 -0700

    userns: Better restrictions on when proc and sysfs can be mounted

    Rely on the fact that another flavor of the filesystem is already
    mounted and do not rely on state in the user namespace.

    Verify that the mounted filesystem is not covered in any significant
    way.  I would love to verify that the previously mounted filesystem
    has no mounts on top but there are at least the directories
    /proc/sys/fs/binfmt_misc and /sys/fs/cgroup/ that exist explicitly
    for other filesystems to mount on top of.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Acked-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
2 files changed