David Howells <dhowells@xxxxxxxxxx> wrote: > The reason that you can do this with open_tree()/move_mount() is that it > allows you to create a mount tree (OPEN_TREE_CLONE) that has no namespace > assignment, pass it through the namespace switch and then attach it inside the > child namespace. The cross-namespace checks in do_move_mount() are bypassed > because the root of the newly-cloned mount tree doesn't have one. It's worse than that. The apparently disconnected tree given you by open_tree(OPEN_TREE_CLONE) is still subject to modification by outside forces. All it takes is one shared object within that tree. So I do wonder if it's possible to form a ring, even in an upstream kernel, by using the propagation mechanism to push through an nsfs mount into itself, possibly with a layer of indirection (ie. having two mutually-referential namespaces). David
