CVE-2022-50100

/// Technical description

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

sched/core: Do not requeue task on CPU excluded from cpus_mask

The following warning was triggered on a large machine early in boot on

a distribution kernel but the same problem should also affect mainline.

WARNING: CPU: 439 PID: 10 at ../kernel/workqueue.c:2231 process_one_work+0x4d/0x440

Call Trace:

<TASK>

rescuer_thread+0x1f6/0x360

kthread+0x156/0x180

ret_from_fork+0x22/0x30

</TASK>

Commit c6e7bd7afaeb ("sched/core: Optimize ttwu() spinning on p->on_cpu")

optimises ttwu by queueing a task that is descheduling on the wakelist,

but does not check if the task descheduling is still allowed to run on that CPU.

In this warning, the problematic task is a workqueue rescue thread which

checks if the rescue is for a per-cpu workqueue and running on the wrong CPU.

While this is early in boot and it should be possible to create workers,

the rescue thread may still used if the MAYDAY_INITIAL_TIMEOU

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References