Filesystem mounts in user namespaces

The ability to attach a USB device is a higher bar. I was simply pointing out that this situation is not unprecedented. There are scenarios where untrusted users with limited, supervised physical access are expected to be able to plug in their own USB storage devices without compromising the entire system. Any data coming from a removable drive ought to treated as unsanitized input. For that matter, applying the same rule to non-removable drives would help to improve robustness in the face of data corruption.