[CVE-2026-98826][MODERATE 7.0] rtc: ac100: Fix clock provider use-after-free on probe failure [ Upstream

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

CVE: CVE-2026-98826
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: rtc: ac100: Fix clock provider use-after-free on probe failure [ Upstream
Commit: 12bcd20d76703ee2baf52224d287b7fea096b12f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=12bcd20d76703ee2baf52224d287b7fea096b12f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98826
Analysis date: Mon, 19 Oct 2026 03:59:22 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A failed AC100 RTC probe can leave a global clock provider referencing freed device-managed data, allowing later clock consumers to read and potentially dereference stale structured pointers, with failed reprobe and possible kernel crash as the supported practical impacts.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98826 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98826

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
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CVE-2026-98826	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98826 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 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:H/A:H';*CWE-416;*CWE-672;*CWE-401;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'The AC100 RTC probe failure path can leave an OF clock provider registered after its device managed chip clk_data object has been freed. A later clock lookup for the same device tree node passes the dangling object to of_clk_hw_onecell_get, which reads freed num and hws fields and can return a stale clk_hw pointer to a consumer. The demonstrated primitive is a use-after-free read with a likely kernel crash or device initialization failure. A more serious consequence cannot be excluded because the freed object contains pointers that may be used by the clock subsystem after memory reuse. For the CVSS the PR:L value is used for the paranoid score because a local user may contribute to the required memory pressure without controlling the device directly, although reliable triggering normally requires an ENOMEM failure during probe and a later clock lookup. AC:H reflects this narrow timing and state requirement. The issue is not network reachable and affects systems with the AC100 RTC and a matching device tree clock consumer. Impact is at least local denial of service and the stale pointer path may allow confidentiality or integrity impact if the freed allocation is reused in a controllable way. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 5 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 ActionableScore threshold rule 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_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4. The independent weaker Aegis shadow evaluated CVSS 4.1 and ActionableScore 1 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 5)	MAYBE	INIT LEAK ERRORPATH UAF HARDWARE LINUS  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap changed either score.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Conservative signals:

* +2 Real UAF. A failed probe frees device-managed `chip->clk_data`, while the global `of_clk_providers` list retains a provider referencing it. A later `of_clk_hw_onecell_get()` call reads the freed object.
* +1 Secondary registration/index staleness. The stale global provider remains discoverable and is traversed by later clock lookups. This is active state rather than passive diagnostic metadata.
* +1 Concrete persistent resource leak. The RTC 32 kHz clock remains registered on the failed-probe paths and can make reprobe fail with `-EEXIST`.
* Total: 2 + 1 + 1 = 4.

Paranoid additional signal:

* +1 Plausible kernel crash or strong device initialization DoS. The callback reads freed `num` and `hws` fields and may return a stale `clk_hw` pointer for subsequent consumer processing.
* Total: 4 + 1 = 5.

Not awarded:

* No controlled reclaim or attacker-shaped replacement object is established.
* No arbitrary or directed write, callback control, disclosure, or privilege escalation is demonstrated.
* No local-unprivileged bonus is awarded because control of the complete probe-failure and later-lookup sequence is unresolved.
* No hardware penalty is applied merely because AC100-specific hardware is required. The supplied evidence identifies affected boards but does not independently establish a physical-only attacker model or justify treating all such deployments as rare.
* No additional availability point is awarded for the same possible crash.
* No repeated release or refcount signal exists. The first operation is devres cleanup and the later operation is a stale structured read, not a second release of the same reference.
* B5-R does not apply because there is no retry-accumulated OOB write.
* B3-PENDING does not apply because there is no shared-backing data write.
* V32, V33, and V34 do not apply because no SKB checksum metadata corruption exists.
* B4-PENDING does not apply because no authorization decision changes from DENY to ALLOW.

3. Reachability analysis

The vulnerable sequence requires AC100 RTC probe to register the clock provider, followed by failure of `devm_rtc_register_device()` with `-ENOMEM`. Probe unwinding then frees `chip->clk_data` without removing the non-device-managed provider. A later device-tree clock lookup by an existing consumer reaches the dangling provider.

The supplied evidence does not establish that an ordinary user can reliably initiate the probe, force the exact allocation failure, or schedule the later lookup. Local memory pressure may influence the failure condition, but that alone does not prove control of the complete sequence. Conversely, the patch does not establish that host-admin privileges are intrinsically required for every occurrence because probing and consumer lookup may occur automatically during boot or device initialization. Therefore `HostAdminRequired=UNKNOWN`.

No user or network namespace controls this platform-device and OF clock-provider lifecycle, so `NamespaceScopedPrivilege=NO`. There is no network trigger. The hardware and device-tree configuration are prerequisites. This is an ordered failure sequence rather than a race, although the `-ENOMEM` window is narrow.

4. Primitive and severity interpretation

The exact primitive is an active structured-object UAF. Freed `struct clk_hw_onecell_data` storage remains reachable through a provider in a global registration list. `of_clk_hw_onecell_get()` reads `num`, indexes `hws`, and may return a pointer obtained from freed storage to a clock consumer.

This is broader than an immediate cleanup-only stale dereference because the dangling registration survives probe cleanup and is consumed by later active clock lookup operations. It is therefore `CLASS_B`, not `CLASS_C`. It is not `CLASS_A` because controlled reclaim, attacker-controlled replacement contents, arbitrary kernel access, callback redirection, and a completed privilege-escalation chain are not established.

The demonstrated consequences are a genuine post-lifetime read, a persistent clock leak, and failed reprobe. A kernel crash is technically plausible when a stale `clk_hw` pointer is consumed, but it is not shown to be reliable. Confidentiality, integrity compromise, and privilege escalation remain speculative.

`ImportantCandidate=YES` because an active global provider returns pointer-bearing state from freed memory to identified in-tree consumers, leaving exploitation leverage beyond a shallow fault unresolved. `AutoDowngradeAllowed=NO` because automatic closure would discard this concrete active-object lifetime primitive, even though Important severity is not independently proven.

5. One-sentence report phrase

A failed AC100 RTC probe can leave a global clock provider referencing freed device-managed data, allowing later clock consumers to read and potentially dereference stale structured pointers, with failed reprobe and possible kernel crash as the supported practical impacts.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The UAF is concrete and escapes the probe error path into a global provider registry, but attacker control over the failure, memory reuse, and subsequent consumer lookup requires source and deployment-specific verification.

7. Call-site confidence

Call-site confidence: high

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

Patch: rtc: ac100: Fix clock provider use-after-free on probe failure [ Upstream
Commit: 12bcd20d76703ee2baf52224d287b7fea096b12f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=12bcd20d76703ee2baf52224d287b7fea096b12f

Changed files:
  drivers/rtc/rtc-ac100.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=12bcd20d76703ee2baf52224d287b7fea096b12f

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

The original Linux kernel CVE announcement for CVE-2026-98826 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98826

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:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 4
  Paranoid ActionableScore: 5

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).