Comment 34 for bug 2016908

prctl behavior was changed by

c2350a7eca5c UBUNTU: SAUCE: Stacking v38: LSM: Specify which LSM to display

it introduces a short circuit to protect against 2 new lsm prctl commands being invoked without a major lsm, and unfortunately makes the mistake that using lsm_slot == 0 means there are no LSMs present and the default value should be returned.

This however is no longer true as lsm_slot is now only used to track LSMs that need access to secid mappings (major LSMs). Attached is the patch sent to kt to restore behavior