[CVE-2026-64428][LOW] gpio: sch: use raw_spinlock_t in the irq startup path [ Upstream

[CVE-2026-64428][LOW] gpio: sch: use raw_spinlock_t in the irq startup path [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64428
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: gpio: sch: use raw_spinlock_t in the irq startup path [ Upstream
Commit: 3b1aa05ec27eeccc889ecaa3f2d9baa9f453e50d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3b1aa05ec27eeccc889ecaa3f2d9baa9f453e50d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64428
Analysis date: Sat, 25 Jul 2026 14:08:47 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
The SCH GPIO driver used a sleepable spinlock_t in a non-sleepable IRQ startup path on PREEMPT_RT, allowing a local GPIO IRQ setup path to trigger an invalid-context warning and possible DoS on affected systems.

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

The original Linux kernel CVE announcement for CVE-2026-64428 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64428

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-2026-64428	LOW	CHECK WITH IMPACT FROM ORIG NN 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-667;CWE-662;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'The SCH GPIO driver can call sch_irq_unmask during IRQ startup while using a regular spinlock_t based lock. On PREEMPT_RT this lock may become sleepable, so the IRQ startup path can hit a sleeping function called from invalid context warning. This is a local availability issue on systems using the SCH GPIO driver with PREEMPT_RT and a reachable GPIO IRQ setup path. For the CVSS the PR:L is used because a local user or service may need access to GPIO IRQ request functionality, but full administrator privileges are not always required in delegated GPIO environments. The issue is not network reachable. Impact is denial of service only, typically a warning or possible kernel crash depending on RT and panic policy.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)  SKIP CVE-2026-64428 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	LOCK DANGER INIT  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  Possible only if a local user or delegated service can request or configure the affected GPIO IRQ path. In many deployments this may still require elevated permissions or device-specific access.

* Availability impact realistic: +1 in paranoid scoring only
  The observed failure is BUG: sleeping function called from invalid context on PREEMPT_RT. This may become a kernel crash or service-impacting failure depending on lockdep, RT configuration, and panic policy.

Negative or limiting signals:

* Rare AND difficult-to-reach subsystem/configuration: -1
  Requires PREEMPT_RT behavior plus the SCH GPIO driver and a reachable IRQ startup path.

Not applied:

* No memory corruption signal.
  The patch changes spinlock_t to raw_spinlock_t and does not indicate UAF, OOB, double-free, stale pointer reuse, type confusion, arbitrary write, or refcount misuse.

* No privilege escalation plausible signal.
  There is no demonstrated corruption primitive or security-boundary bypass.

* No remote/network trigger.
  This is a local device/IRQ setup path, not packet-triggered.

## 3. Reachability analysis

The bug is triggered through the SCH GPIO IRQ startup path, specifically request_threaded_irq -> __setup_irq -> irq_startup -> sch_irq_unmask -> sch_irq_mask_unmask. It is relevant on PREEMPT_RT kernels because regular spinlock_t can become sleepable there. A practical trigger requires the affected hardware or platform driver and the ability to request or set up the GPIO IRQ. Namespace or container delegation could lower practical privileges if GPIO access is exposed, but this is not a broadly default unprivileged interface. The path is not network reachable.

## 4. Severity interpretation

This behaves like a low-end Moderate or Low-like availability issue rather than an Important-class vulnerability. The realistic impact is an invalid-context sleeping-lock warning and possible local DoS under PREEMPT_RT-specific conditions. Theoretical escalation is not supported by the patch because there is no memory lifetime bug, no write primitive, and no sensitive security-boundary bypass. The issue should not be treated as actionable Moderate unless the evaluated product commonly ships PREEMPT_RT with SCH GPIO IRQ access exposed to untrusted local users.

## 5. One-sentence report phrase

The SCH GPIO driver used a sleepable spinlock_t in a non-sleepable IRQ startup path on PREEMPT_RT, allowing a local GPIO IRQ setup path to trigger an invalid-context warning and possible DoS on affected systems.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a configuration-specific PREEMPT_RT locking correctness issue with DoS-only impact and no evidence of memory corruption, privilege escalation, or network reachability.

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

Patch: gpio: sch: use raw_spinlock_t in the irq startup path [ Upstream
Commit: 3b1aa05ec27eeccc889ecaa3f2d9baa9f453e50d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3b1aa05ec27eeccc889ecaa3f2d9baa9f453e50d

Changed files:
  drivers/gpio/gpio-sch.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=3b1aa05ec27eeccc889ecaa3f2d9baa9f453e50d

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

The original Linux kernel CVE announcement for CVE-2026-64428 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64428

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).