CVE-2024-56583

What it actually does

Incorrectly calls setup_new_dl_entity on already-boosted deadline tasks during CPU migration with ENQUEUE_RESTORE, triggering a WARN_ON in the scheduler.

Why it matters to the business

Linux systems using deadline scheduling may log spurious kernel warnings and experience unexpected scheduler behavior under load or task migration, reducing reliability of real-time workloads.

How an attack unfolds

A workload or local process repeatedly triggers task migrations on boosted deadline tasks through signals or affinity changes, causing the scheduler to re-invoke setup_new_dl_entity and hit the warning condition.

How to fix it

Update the Linux kernel to the version containing commit b600d30402854415aa57548a6b53dc6478f65517 that adds a check to skip setup_new_dl_entity for boosted tasks during requeue.

How to confirm the fix worked

Confirm the running kernel includes commit b600d30402854415aa57548a6b53dc6478f65517 and re-run the provided stress-ng cyclic test to verify absence of the warning.

Typical attack path

1. Launch cyclic real-time workload with stress-ng
2. Trigger repeated CPU migrations via signals or kill operations
3. Invoke migrate_enable on boosted deadline tasks
4. Observe WARN_ON in setup_new_dl_entity

How to detect it

Search kernel logs and dmesg for entries containing setup_new_dl_entity, deadline.c:794, or migrate_enable combined with rt_spin_unlock or kill operations.

What your security team should do

• Apply the fixed kernel commit or distribution update containing b600d30402854415aa57548a6b53dc6478f65517 as soon as available
• Monitor kernel logs for deadline scheduler warnings
• Restrict deadline scheduling policies on unpatched systems if feasible