[CVE-2026-89769][MODERATE REGULAR] clocksource/drivers/nxp-pit: Fix IRQ leak on cpuhp_setup_state error path

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

CVE: CVE-2026-89769
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: clocksource/drivers/nxp-pit: Fix IRQ leak on cpuhp_setup_state error path
Commit: d53c29a89a15e56a1797f3ef249955e544782e04
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d53c29a89a15e56a1797f3ef249955e544782e04
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89769
Analysis date: Fri, 11 Sep 2026 23:51:13 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89769 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89769

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 REGULAR
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-2026-89769	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89769 CHECK WITH IMPACT FROM ORIG NN LOW	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-459;*CWE-772;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'An error path in the NXP PIT clocksource driver can leave an IRQ registered after the associated pit object has been freed. The stale IRQ dev_id then points to released memory and a later interrupt can cause the handler to dereference that memory, creating a use-after-free condition. Impact is at least a local denial of service through a kernel crash. Reuse of the freed allocation before the interrupt may also permit confidentiality or integrity impact and in the worst defensible case could support privilege escalation. For the CVSS the PR:L value is used for the paranoid score because a reduced capability local service or delegated device management process may be able to influence driver lifecycle or CPU hotplug related conditions without having unrestricted host administration rights. Attack complexity is high because cpuhp_setup_state must fail after request_irq succeeds and the IRQ must fire after pit is freed. The issue is not network reachable and applies only to systems using the affected NXP PIT driver and hardware.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)  SKIP CVE-2026-89769 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	INIT LEAK ERRORPATH UAF HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap changed the result. The Real UAF floor was not applied because this is fixed stale driver storage reached through a narrow initialization error path, with no established below-host-admin trigger or meaningful reuse primitive.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Positive signals:

* +2 Real UAF and lifetime violation. `request_irq()` registers `pit` as the interrupt handlers `dev_id`, the error path later executes `kfree(pit)` without first unregistering the IRQ, and a subsequent interrupt can dereference the freed context.
* +1 Concrete persistent kernel resource leak. The registered IRQ is not released on the affected error path.
* +1 Reliable kernel crash or strong DoS. Invoking the interrupt handler with a dangling `dev_id` can produce a host kernel fault.

Negative signals:

* -2 Physical-only or rare hardware-only path. The vulnerable driver specifically supports NXP Automotive S32G2 and S32G3 PIT hardware, which is materially required to reach this initialization path.

Not awarded:

* No remote or ordinary local-user reachability is established.
* No controlled reclaim, attacker-shaped replacement object, directed write, disclosure, callback control, or refcount takeover is demonstrated.
* Structured stale-object leverage is not awarded. Although `pit` is a structured driver context, the supplied evidence establishes only an IRQ callback using the fixed stale address.
* Weak or strong LPE points are not awarded merely because heap reuse is theoretically possible.
* No extra Availability point is awarded because it would duplicate the same kernel-crash consequence.
* No Confidentiality or Integrity points are awarded because no useful disclosure or modification primitive is established.
* No timing penalty is applied. This is an ordered initialization error path, not an independently established hard race.
* No concrete repeated release or refcount signal exists. There is one missing IRQ release followed by stale handler use, not a second lifetime-mutating operation on `pit`.
* Paranoid repeated-refcount leverage does not apply.
* FLOOR 5 does not apply.

Arithmetic:

* Conservative: `+2 UAF +1 IRQ leak +1 crash -2 rare physical hardware = 2`.
* Paranoid: the same result. Increasing the score would require an additional primitive not established by the supplied patch.

3. Reachability analysis

The vulnerable sequence occurs during initialization of the global NXP PIT clocksource driver. `request_irq()` must first succeed, `cpuhp_setup_state()` must then fail, cleanup must free `pit` without releasing the IRQ, and that IRQ must subsequently fire.

No ordinary-user, delegated-service, or network interface capable of inducing this complete sequence is established. Host-admin-equivalent privilege is also not positively proven as an attacker requirement, so `HostAdminRequired` remains `UNKNOWN` rather than being assumed `YES`.

The operation is not namespace scoped. Clocksource initialization, CPU hotplug state registration, and the physical IRQ are global kernel facilities rather than resources controlled through an attacker-created user or network namespace.

The affected NXP Automotive hardware and matching device-tree or platform setup are prerequisites. An attacker cannot instantiate this physical timer from an ordinary namespace. This is an initialization error sequence rather than a repeatable userspace-controlled race.

4. Primitive and severity interpretation

The exact primitive is an asynchronous post-free dereference through an IRQ registration whose `dev_id` continues to reference a freed `struct pit_timer`. This is a real Class B lifetime violation.

The object is best classified as fixed stale driver storage. The stale address remains registered with the IRQ subsystem, but no controlled replacement or attacker influence over reclaimed contents is shown. The stale use occurs after initialization failure and cleanup rather than through a general attacker-controlled active-object API.

There is no repeated release or refcount mutation. The missing `free_irq()` creates the dangling registration, but the later IRQ handler invocation is an ordinary stale-object dereference rather than a second `put`, `free`, or refcount update on the same object.

The demonstrated consequences are an IRQ leak and potential kernel crash. Privilege escalation or confidentiality and integrity effects remain generic UAF possibilities rather than patch-supported primitives.

`ImportantCandidate=NO` because this is a constrained, hardware-specific, fixed-context UAF without meaningful demonstrated reuse leverage. `AutoDowngradeAllowed=YES` because the unresolved evidence does not establish controlled corruption, repeated lifetime mutation, security-boundary bypass, or an attacker-reachable active-object exploitation surface.

5. One-sentence report phrase

An NXP PIT initialization failure can leave an IRQ registered with a freed driver context as its dev_id, allowing a later interrupt to cause a constrained use-after-free and kernel crash on affected S32G2 or S32G3 systems.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether the driver can be reprobed or its initialization failure induced after boot, and inspect the IRQ handler for any post-free field use that could provide leverage beyond an immediate fault.

7. Call-site confidence

Call-site confidence: medium

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

Patch: clocksource/drivers/nxp-pit: Fix IRQ leak on cpuhp_setup_state error path
Commit: d53c29a89a15e56a1797f3ef249955e544782e04
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d53c29a89a15e56a1797f3ef249955e544782e04

Commit description:

When cpuhp_setup_state fails after pit_clockevent_per_cpu_init has
successfully called request_irq, the error handling jumps directly to
out_pit_clocksource_unregister without freeing the registered IRQ.

This leaks the IRQ line and, since kfree(pit) follows, leaves a
dangling pointer registered as the interrupt handler's dev_id,
potentially leading to a use-after-free if the IRQ fires afterwards.

Fix it by calling pit_clockevent_per_cpu_exit to properly release the
IRQ before falling through to the existing cleanup chain.

Suggested-by: Greg KH <gregkh@linuxfoundation.org>
Fixes: bee33f2 ("clocksource/drivers/nxp-pit: Add NXP Automotive s32g2 / s32g3 support")
Cc: stable@vger.kernel.org
Signed-off-by: WenTao Liang <vulab@iscas.ac.cn>
Signed-off-by: Daniel Lezcano <daniel.lezcano@kernel.org>
Link: https://patch.msgid.link/20260628130700.45680-1-vulab@iscas.ac.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/clocksource/timer-nxp-pit.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=d53c29a89a15e56a1797f3ef249955e544782e04

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

The original Linux kernel CVE announcement for CVE-2026-89769 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89769

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:L/I:L/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: unknown
  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: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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.
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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
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