Users must not be allowed to step outside the volume with subPath.
Therefore the final subPath directory must be "locked" somehow
and checked if it's inside volume.
On Windows, we lock the directories. On Linux, we bind-mount the final
subPath into /var/lib/kubelet/pods/<uid>/volume-subpaths/<container name>/<subPathName>,
it can't be changed to symlink user once it's bind-mounted.
Kubelet makes sure that /var/lib/kubelet is rshared when it starts.
If not, it bind-mounts it with rshared propagation to containers
that mount volumes to /var/lib/kubelet can benefit from mount propagation.
Added IsNotMountPoint method to mount utils (pkg/util/mount/mount.go)
Added UnmountMountPoint method to volume utils (pkg/volume/util/util.go)
Call UnmountMountPoint method from local storage (pkg/volume/local/local.go)
IsLikelyNotMountPoint behavior was not modified, so the logic/behavior for UnmountPath is not modified
With bug #27653, kubelet could remove mounted volumes and delete user data.
The bug itself is fixed, however our trust in kubelet is significantly lower.
Let's add an extra version of RemoveAll that does not cross mount boundary
(rm -rf --one-file-system).
It calls lstat(path) three times for each removed directory - once in
RemoveAllOneFilesystem and twice in IsLikelyNotMountPoint, however this way
it's platform independent and the directory that is being removed by kubelet
should be almost empty.
Jan Safranek