selftests/filesystems: check that an unmounted mount tree isn't walked

Add unmounted_tree_test:

- a detached nsfs or pidfs bind mount that a file descriptor keeps
  alive can't be copied recursively, a copy of the mount itself and
  a copy of a mounted one still work
- a detached tree with a child that was vacated behind it can't be
  copied recursively either
- a copy of a detached bind mount is an ordinary mount: unlinking its
  mountpoint from another mount namespace unmounts it
- mount_setattr() refuses to change the propagation of a detached
  tree and still allows it for the root of an anonymous mount
  namespace

Every case runs in a user and mount namespace of its own.

Link: https://patch.msgid.link/20260926-work-mount-fixes-2-v1-9-f357abf3d17b@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

0 files changed, 0 insertions, 0 deletions