CVE-2023-52704

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.