CVE-2023-52704: Undefined Security Weakness

In the Linux kernel, the following vulnerability has been resolved:

freezer,umh: Fix call_usermode_helper_exec() vs SIGKILL

Tetsuo-San noted that commit f5d39b020809 ("freezer,sched: Rewrite core freezer logic") broke call_usermodehelper_exec() for the KILLABLE case.

Specifically it was missed that the second, unconditional, wait_for_completion() was not optional and ensures the on-stack completion is unused before going out-of-scope.