[CVE-2026-98942][MODERATE 7.0] sched_ext: Build the cid tables privately and publish them with RCU [ Upstream

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

CVE: CVE-2026-98942
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: sched_ext: Build the cid tables privately and publish them with RCU [ Upstream
Commit: 0e1a74369bdbc357d3d9713734418d914a981553
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0e1a74369bdbc357d3d9713734418d914a981553
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98942
Analysis date: Mon, 26 Oct 2026 23:52:37 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A sched_ext cid-table publication and RCU lifetime race can expose uninitialized heap contents or let BPF kfunc readers dereference retired structured tables.

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

The original Linux kernel CVE announcement for CVE-2026-98942 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98942

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: MODERATE 7.0
Manual review required: YES

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-2026-98942	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98942 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:H';CWE-362;CWE-908;*CWE-200;*CWE-416;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L';BEST CVSS score: '6.5';DESCR 'A publication and lifetime race in sched_ext cid tables allows BPF cid kfunc readers to observe entries while kmalloc backed tables are incomplete, rewritten in place, or being retired. A racing TRACING or SYSCALL BPF program may receive uninitialized kernel data or a torn topology mapping, and missing RCU protection in scx_bpf_this_cid and sleepable scx_bpf_task_cid creates a plausible stale pointer or UAF dereference risk during table replacement or scheduler shutdown. For the CVSS the PR:L value reflects that local execution plus permission to load an eligible BPF program is required, while full system administration is not necessarily required in deployments that delegate BPF capabilities. AC:H reflects the need to race table publication, initialization, replacement, or retirement. The demonstrated primitive supports confidentiality and mapping integrity impact, while the worst grounded case includes a kernel crash. No arbitrary write or proven privilege escalation primitive is established. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 6.5 and the production ActionableScore returned 4 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the manual review requirement was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK. The independent weaker Aegis shadow evaluated CVSS 2.7 and ActionableScore 4 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 4)	MAYBE	 KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	-	-	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 4.
* Conservative score: 4; no floor or cap changed it.
* Raw paranoid score: 4.
* Paranoid score: 4; no additional exploit primitive is sufficiently established.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 Real UAF/lifetime violation: cid table pointers could remain visible to readers during replacement or retirement without adequate RCU protection; the fix privately builds, atomically publishes, unpublishes, and RCU-frees them.
* +1 Confidentiality plausible: BPF cid kfuncs could return entries read from uninitialized kmalloc-backed table storage.
* +1 Reliable kernel crash plausible: an unprotected reader can dereference table storage across retirement, supporting a stale-pointer fault.
* No race penalty: racing is required, but the evidence does not establish a narrow, one-shot, or materially uncontrollable race.
* No structured-leverage bonus: readers consume topology entries, but attacker-controlled reclaim, replacement contents, pointers, callbacks, or memory-access fields are not shown.
* No integrity bonus: torn or stale cid mappings are demonstrated, but unauthorized modification of protected state is not.
* No arbitrary write, controlled reclaim, LPE, remote trigger, or extra availability point is awarded.

3. Reachability analysis

A local TRACING or SYSCALL BPF program can invoke the affected kfunc readers. Loading such programs is privilege-gated, while the complete relationship between BPF loading rights and control of root sched_ext enable, re-enable, initialization, or shutdown is not shown. Delegated BPF capability is credible but does not prove that one below-host-admin actor controls the full race. Namespace-scoped completion and host UID 0 requirements therefore remain unknown. No hardware prerequisite is indicated.

4. Primitive and severity reading

The primitive is an active structured-table publication and lifetime race, not fixed stale storage: readers can observe uninitialized or torn entries and may dereference retired heap storage. Use occurs during ordinary kfunc lookup as well as scheduler transitions, rather than only in a destructor. This is CLASS_B, not CLASS_A, because no controlled reclaim or directed corruption is shown.

ImportantCandidate is YES because the real RCU lifetime breach has a demonstrated kernel-data exposure path and unresolved post-retirement behavior. Auto-downgrade is unsafe until the complete privilege boundary and stale-table consumption are reviewed. B4 does not apply because no authorization DENY-to-ALLOW transition exists.

5. One-sentence report phrase

A sched_ext cid-table publication and RCU lifetime race can expose uninitialized heap contents or let BPF kfunc readers dereference retired structured tables.

6. Manual review advice

MANUAL CHECK REQUIRED

Confirm the complete BPF/sched_ext privilege model, table-retirement call paths, disclosure width, and whether repeated reads can obtain useful stale heap data.

7. Call-site confidence

Call-site confidence: medium

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

Patch: sched_ext: Build the cid tables privately and publish them with RCU [ Upstream
Commit: 0e1a74369bdbc357d3d9713734418d914a981553
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0e1a74369bdbc357d3d9713734418d914a981553

Changed files:
  kernel/sched/ext/internal.h
  kernel/sched/ext/sub.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=0e1a74369bdbc357d3d9713734418d914a981553

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

The original Linux kernel CVE announcement for CVE-2026-98942 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98942

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:L/I:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:H
  The Best / paranoid CVSS score: 6.5

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: unknown
  Paranoid ActionableScore: 4

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: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).