On Tue, Mar 11, 2025 at 12:01:48PM +0100, Christian Brauner wrote: > The case where arbitrary devices stuck into a laptop (e.g., USB sticks) > are mounted isn't solved by making a filesystem mountable unprivileged. > The mounted device cannot show up in the global mount namespace > somewhere since the user doesn't own the initial mount+user namespace. > So it's pointless. In other words, there's filesystem level checks and > mount namespace based checks. Circumventing that restriction means that > any user can just mount the device at any location in the global mount > namespace and therefore simply overmount other stuff. Note that "untrusted contents" is not the worst thing you can run into - it can be content changing behind your back. I seriously doubt that anyone fuzzes for that kind of crap (and no, it's not an invitation to start). I seriously doubt that there's any local filesystem that would be resilent to that...
