commit 87a8ebd637dafc255070f503909a053cf0d98d3f
author Eric W. Biederman <ebiederm@xmission.com> Sun Mar 24 14:28:27 2013 -0700
committer Eric W. Biederman <ebiederm@xmission.com> Wed Mar 27 07:50:08 2013 -0700
tree 0bc879f9118c3333c73dfd15223a79e6219f64fd
parent a636b702ed1805e988ad3d8ff8b52c060f8b341c

userns: Restrict when proc and sysfs can be mounted

Only allow unprivileged mounts of proc and sysfs if they are already
mounted when the user namespace is created.

proc and sysfs are interesting because they have content that is
per namespace, and so fresh mounts are needed when new namespaces
are created while at the same time proc and sysfs have content that
is shared between every instance.

Respect the policy of who may see the shared content of proc and sysfs
by only allowing new mounts if there was an existing mount at the time
the user namespace was created.

In practice there are only two interesting cases: proc and sysfs are
mounted at their usual places, proc and sysfs are not mounted at all
(some form of mount namespace jail).

Cc: stable@vger.kernel.org
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>