CVE-2025-21897 Affecting kernel-uek-debug package, versions <0:6.12.0-101.33.4.3.el9uek


Severity

Recommended
high

Based on Oracle Linux security rating.

Threat Intelligence

EPSS
0.03% (6th percentile)

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  • Snyk IDSNYK-ORACLE9-KERNELUEKDEBUG-10779833
  • published18 Jul 2025
  • disclosed1 Apr 2025

Introduced: 1 Apr 2025

CVE-2025-21897  (opens in a new tab)

How to fix?

Upgrade Oracle:9 kernel-uek-debug to version 0:6.12.0-101.33.4.3.el9uek or higher.
This issue was patched in ELSA-2025-20480.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-uek-debug package and not the kernel-uek-debug package as distributed by Oracle. See How to fix? for Oracle:9 relevant fixed versions and status.

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

sched_ext: Fix pick_task_scx() picking non-queued tasks when it's called without balance()

a6250aa251ea ("sched_ext: Handle cases where pick_task_scx() is called without preceding balance_scx()") added a workaround to handle the cases where pick_task_scx() is called without prececing balance_scx() which is due to a fair class bug where pick_taks_fair() may return NULL after a true return from balance_fair().

The workaround detects when pick_task_scx() is called without preceding balance_scx() and emulates SCX_RQ_BAL_KEEP and triggers kicking to avoid stalling. Unfortunately, the workaround code was testing whether @prev was on SCX to decide whether to keep the task running. This is incorrect as the task may be on SCX but no longer runnable.

This could lead to a non-runnable task to be returned from pick_task_scx() which cause interesting confusions and failures. e.g. A common failure mode is the task ending up with (!on_rq && on_cpu) state which can cause potential wakers to busy loop, which can easily lead to deadlocks.

Fix it by testing whether @prev has SCX_TASK_QUEUED set. This makes @prev_on_scx only used in one place. Open code the usage and improve the comment while at it.

CVSS Base Scores

version 3.1