Executive brief
In the Linux kernel, the following vulnerability has been resolved:
s390/debug: Fix NULL pointer dereference in debug_set_level()
Commit a2cec6863709 ("s390/debug: Add s390dbf kernel parameter") incorrectly removed a null-id check from debug_set_level(), introducing a possible NULL pointer dereference for debug-API users that put debug_register() results unchecked into debug_set_level().
Fix this by moving the check from the internal _debug_set_level() variant back to the external debug_set_level() wrapper.