[CVE-2026-98623][LOW] drm/nouveau/clk: fix list cursor use after loop in nvkm_clk_ustate_update [ Upstream

[CVE-2026-98623][LOW] drm/nouveau/clk: fix list cursor use after loop in nvkm_clk_ustate_update [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98623
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/nouveau/clk: fix list cursor use after loop in nvkm_clk_ustate_update [ Upstream
Commit: db5dd9f47b4df1be322f498d846e9a82940a7390
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=db5dd9f47b4df1be322f498d846e9a82940a7390
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98623
Analysis date: Sun, 18 Oct 2026 23:13:07 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
An invalid Nouveau pstate debugfs request can make nvkm_clk_ustate_update read beyond a real nvkm_pstate object by dereferencing the synthetic list cursor after an unsuccessful traversal, but no disclosure, write, UAF, or privilege escalation is established.

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

The original Linux kernel CVE announcement for CVE-2026-98623 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98623

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.

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

CVE-2026-98623	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98623 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT LOW AEGIS_AS=1 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both LOW)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L';CWE-125;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'An invalid list cursor is dereferenced after nvkm_clk_ustate_update fails to find the requested pstate or processes an empty state list. The cursor then represents the list head cast as struct nvkm_pstate, so reading pstate.pstate performs an out-of-bounds read rather than a use-after-free. A local user can reach this path by supplying an unknown pstate identifier through the Nouveau pstate debugfs interface. For the CVSS the PR:L value is used for the paranoid score because some systems may delegate GPU management or debugfs access to a restricted service or container, although the interface is normally writable only by an administrator. The demonstrated primitive is an invalid read with no supported arbitrary write. The realistic impact is a failed control operation or limited GPU availability impact. A limited information or integrity effect remains possible if the invalid value affects the comparison and subsequent state selection, but host privilege escalation is not established. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 5.3 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to LOW because the ActionableScore threshold 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_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH and INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 1 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	OOB SIMPLEFIX HARDWARE DEBUGFS TEST  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

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

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Weak or indirect corruption candidate. An unsuccessful list traversal leaves `pstate` as a synthetic container pointer derived from the list head, and `pstate->pstate` performs a confirmed out-of-bounds read.
* No Local unprivileged trigger point. The commit establishes userspace reachability through debugfs but does not establish that an ordinary user can write the relevant file.
* No crash point. The patch does not establish an Oops, panic, device failure, or host-wide denial of service.
* No confidentiality point. The value read outside the intended object is only used in an internal comparison and no disclosure path is shown.
* No integrity point. The comparison can influence whether the request is accepted, but no subsequent unauthorized write or protected-state modification is established.
* No UAF, OOB write, controlled reclaim, arbitrary write, callback influence, authorization bypass, or privilege-escalation primitive is demonstrated.
* NEW52 B5-R does not apply because there is no heap OOB write, retry accumulation, or later consumption of corrupted writable state.
* NEW53 B3-PENDING does not apply because no shared-backing write exists.
* V33 and V32 do not apply because no attacker-influenced write into active structured state or checksum metadata exists.
* B4-PENDING does not apply because the patch fixes iterator-result validation, not a DENY-to-ALLOW authorization decision.

3. Reachability analysis

The trigger is a write of an unknown pstate identifier to the Nouveau `pstate` debugfs interface. It is also reachable with any identifier when the performance-state list is empty because of broken performance tables.

The supplied evidence does not establish the file ownership or mode, so effective host-administrator requirements remain unknown. It also does not establish an ordinary logged-in user, DRM master, compositor, or delegated graphics service as able to complete the trigger. The interface is global debugfs state rather than a user-namespace-scoped facility, so `NamespaceScopedPrivilege=NO`.

Prerequisites include the Nouveau driver, exposed debugfs control, `allow_reclock`, and either an unmatched identifier or an empty state list. No race or special timing is required. NVIDIA hardware is required, but no rare-hardware penalty is justified merely because this is a GPU driver.

4. Primitive and severity interpretation

The exact primitive is a limited out-of-bounds read caused by treating the list head as `struct nvkm_pstate` after `list_for_each_entry()` completes without finding a match. This is not a real object after its lifetime and therefore is not a UAF.

The invalid value participates in an equality comparison. If it happens to equal the requested identifier, execution can continue with `req` derived from the traversal count. However, the supplied context does not establish a subsequent OOB write, sensitive disclosure, kernel crash, or protected-state modification.

This is CLASS_C because the demonstrated behavior is an invalid internal read and invalid-state decision without an independently useful corruption primitive. `ImportantCandidate=NO` and `AutoDowngradeAllowed=YES` are appropriate because no unresolved write, lifetime, authorization, ownership, or cross-boundary primitive remains.

5. One-sentence report phrase

An invalid Nouveau pstate debugfs request can make nvkm_clk_ustate_update read beyond a real nvkm_pstate object by dereferencing the synthetic list cursor after an unsuccessful traversal, but no disclosure, write, UAF, or privilege escalation is established.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The confirmed primitive is a limited local OOB read with unresolved debugfs permissions and no demonstrated disclosure, corruption, crash, or authorization boundary impact.

7. Call-site confidence

Call-site confidence: medium

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

Patch: drm/nouveau/clk: fix list cursor use after loop in nvkm_clk_ustate_update [ Upstream
Commit: db5dd9f47b4df1be322f498d846e9a82940a7390
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=db5dd9f47b4df1be322f498d846e9a82940a7390

Changed files:
  drivers/gpu/drm/nouveau/nvkm/subdev/clk/base.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=db5dd9f47b4df1be322f498d846e9a82940a7390

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

The original Linux kernel CVE announcement for CVE-2026-98623 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98623

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:L/PR:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
  The Best / paranoid CVSS score: 5.3

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: 1

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).