CVE-2023-52942

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

cgroup/cpuset: Fix wrong check in update_parent_subparts_cpumask()

It was found that the check to see if a partition could use up all the cpus from the parent cpuset in update_parent_subparts_cpumask() was incorrect. As a result, it is possible to leave parent with no effective cpu left even if there are tasks in the parent cpuset. This can lead to system panic as reported in [1].

Fix this probem by updating the check to fail the enabling the partition if parent's effective_cpus is a subset of the child's cpus_allowed.

Also record the error code when an error happens in update_prstate() and add a test case where parent partition and child have the same cpu list and parent has task. Enabling partition in the child will fail in this case.

[1] https://www.spinics.net/lists/cgroups/msg36254.html