Add a test for open_tree(OPEN_TREE_NAMESPACE) from a user namespace that doesn't own the mount namespace it copies from: - a file covered by a private or an unbindable tmpfs mount - the non-recursive copy of the parent mount fails with EINVAL - the recursive copy keeps the file covered in the new mount namespace - the owner of the mount namespace keeps the bind mount semantics Link: https://patch.msgid.link/20260930-work-mount-fixes-3-v1-7-be34c83956ae@kernel.org Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>