[CVE-2026-98864][LOW] sched_ext: Wait for SCX_OPSS_DISPATCHING before reenqueueing a task [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-98864
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: sched_ext: Wait for SCX_OPSS_DISPATCHING before reenqueueing a task [ Upstream
Commit: 43457bf6550044c40bd6d3fcdf9ea66f5a55d139
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=43457bf6550044c40bd6d3fcdf9ea66f5a55d139
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98864
Analysis date: Sat, 24 Oct 2026 06:47:44 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A narrow `sched_ext` state race can erase a task’s queued state and indefinitely suppress its later dispatches, causing task starvation without demonstrated memory corruption or privilege-boundary impact.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98864 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98864

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-98864	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98864 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=1 LEGACY=LOW RESULT=DIFF (final Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A state race in sched_ext can occur when a task is visible on a DSQ while its ops_state is still SCX_OPSS_DISPATCHING. A concurrent reenqueue can set SCX_OPSS_QUEUED before the dispatcher performs its delayed final store of SCX_OPSS_NONE. The delayed store then clobbers the queued state and finish_dispatch drops every later dispatch of the affected task. The demonstrated primitive is task starvation and scheduler availability loss rather than UAF OOB access or other memory corruption. For the CVSS the PR:L value reflects that reliable attacker directed triggering requires local task activity in a system already using sched_ext while the narrow race window makes AC:H appropriate. Base availability impact is limited to the affected task. The paranoid score uses A:H because loss of a critical task could cause broader service disruption while C and I remain N. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE to LOW because the ActionableScore threshold rule was applied. final reconciliation stage LOW to LOW because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 and KPANIC_UNSUPPORTED_REMOVED and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 3.1 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	DANGER LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 KPANIC_UNSUPPORTED_REMOVED V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 1.
* Conservative score: 1; no floor or cap applied.
* Raw paranoid score: 2.
* Paranoid score: 2; no floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 weak active-state corruption: a reenqueue stores `SCX_OPSS_QUEUED`, then the dispatcher's delayed final store clobbers it with `SCX_OPSS_NONE`.
* +1 availability impact: `finish_dispatch()` subsequently drops later dispatches, potentially starving the affected task.
* -1 conservative timing penalty: the supplied evidence characterizes the required DSQ-visible/`SCX_OPSS_DISPATCHING` interval as a narrow race.
* Paranoid difference: the -1 is withheld because the patch does not quantify reliability or show that repeated task activity cannot amplify attempts.
* No UAF, OOB access, arbitrary write, controlled reclaim, kernel crash, authorization bypass, confidentiality impact, or protected-state integrity impact is shown.
* NEW52/B5-R does not apply: there is no heap OOB write or retry-accumulated offset.
* V33 does not apply: although active scheduler state is clobbered and later consumed, no credible guest, namespace, or delegated-interface boundary is established.

3. Reachability analysis

The affected system must already be using `sched_ext`, implying prior scheduler setup, but the supplied source does not establish who can force the complete reenqueue/dispatch interleaving. Local task activity may contribute, yet normal-user, delegated-capability, and namespace-complete triggering remain unproven. No special hardware is required. Race repeatability is unresolved beyond the supplied “narrow window” characterization.

4. Primitive and severity reading

The primitive is a synchronization-induced scheduler state loss, not memory corruption: a valid state store overwrites a newer valid state, causing later task dispatches to be discarded. The shown consequence is starvation of an affected task and possible service disruption. Host panic or broader scheduler failure is not demonstrated. This is CLASS_C availability behavior with no separate non-crash exploitation primitive, so it is not an Important candidate and may be auto-downgraded.

5. One-sentence report phrase

A narrow `sched_ext` state race can erase a task’s queued state and indefinitely suppress its later dispatches, causing task starvation without demonstrated memory corruption or privilege-boundary impact.

6. Manual review advice

NO MANUAL CHECK NEEDED

The patch-supported impact is constrained scheduler availability loss with no unresolved corruption or authorization primitive.

7. Call-site confidence

Call-site confidence: high

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: sched_ext: Wait for SCX_OPSS_DISPATCHING before reenqueueing a task [ Upstream
Commit: 43457bf6550044c40bd6d3fcdf9ea66f5a55d139
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=43457bf6550044c40bd6d3fcdf9ea66f5a55d139

Changed files:
  kernel/sched/ext/ext.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=43457bf6550044c40bd6d3fcdf9ea66f5a55d139

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98864 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98864

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 1
  Paranoid ActionableScore: 2

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).