[CVE-2026-74604][MODERATE 7.0] Revert "thermal/drivers/hwmon: Cleanup coding style a bit"

[CVE-2026-74604][MODERATE 7.0] Revert "thermal/drivers/hwmon: Cleanup coding style a bit"

[AL-KERNEL]

CVE: CVE-2026-74604
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Revert "thermal/drivers/hwmon: Cleanup coding style a bit"
Commit: 2434f4765da8ccd7ef31be88b86f1bfa2e95be11
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2434f4765da8ccd7ef31be88b86f1bfa2e95be11
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74604
Analysis date: Sat, 22 Aug 2026 16:59:52 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
`thermal_add_hwmon_sysfs() could free an existing shared hwmon object on an error path, creating a local use-after-free risk with likely DoS impact and possible LPE concern requiring manual review.`

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

The original Linux kernel CVE announcement for CVE-2026-74604 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74604

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.

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

CVE-2026-74604	MODERATE	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-664;CWE-703;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'thermal_add_hwmon_sysfs() could free an existing shared hwmon object on an error path instead of freeing only a newly allocated object. This creates a use-after-free candidate because the object may still be reachable from thermal or hwmon state after the failed setup path returns. For the CVSS the PR:L is used in the paranoid score because triggering normally requires local ability to influence thermal device registration or driver setup, but this control may be available to a less privileged service or delegated device management context in some deployments. The issue is not network reachable. Impact is at least local denial of service via kernel crash, and in the worst case may allow confidentiality or integrity impact due to kernel memory corruption and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	ERRORPATH UAF IMPROVEONLY  INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Generic memory corruption: +2. The commit explicitly says the removed check introduced a use-after-free in `thermal_add_hwmon_sysfs()`.
* Real lifetime corruption: +1. The bug is an incorrect free of `hwmon` on an error path, leaving possible stale references to an existing shared object.
* Weak LPE concern: +1. UAF exists, but the patch does not show attacker-controlled reclaim, object replacement, callback control, type confusion, or write-after-free.
* Privileged kernel/device-management memory corruption path: +1. The bug is in thermal hwmon device/sysfs registration and cleanup.
* Requires admin/root/CAP or privileged device-management context in typical deployments: -2. Reliable triggering likely requires thermal device registration, driver setup, module/device management, or fault-injection-like control.
* Error-path and special-condition trigger: -1. The UAF is in an error path, not a common steady-state data path.

Paranoid adjustment:

* Local lower-privilege or delegated device-management trigger: +1. In some deployments, a service, container root, or reduced-capability management context may influence device registration or driver setup without being equivalent to full host root.

## 3. Reachability analysis

The issue is local, not network reachable. A realistic trigger requires causing `thermal_add_hwmon_sysfs()` to enter the relevant error path while `hwmon` refers to an already existing object rather than a newly allocated one. In normal systems this is usually tied to privileged device or driver lifecycle operations, ACPI or platform thermal device setup, module load or unload, hotplug, or fault injection. Namespaces do not obviously make this reachable by a fully unprivileged user, but delegated device-management or reduced-root environments can lower the practical privilege boundary. The path is not a broad packet-processing or syscall-fast-path exposure.

Call-site confidence: medium. The patch shows the exact bad free site and the guarding condition, but not all callers and later stale-reference users.

## 4. Severity interpretation

This is stronger than an ordinary Moderate cleanup because the patch explicitly fixes a UAF, a real kernel lifetime corruption class. However, the exploitation evidence is limited: the bug is in a privileged error path and does not show controlled reclaim, arbitrary write, callback dispatch, or a demonstrated LPE primitive. Realistic impact is most likely local kernel crash or unstable device/sysfs state. Paranoid handling is justified because UAFs can sometimes become privilege escalation after deeper object-lifetime analysis, so this should not be auto-closed.

## 5. One-sentence report phrase

`thermal_add_hwmon_sysfs() could free an existing shared hwmon object on an error path, creating a local use-after-free risk with likely DoS impact and possible LPE concern requiring manual review.`

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: explicit UAF in kernel lifetime management code. The current patch does not prove a strong exploit primitive, but the bug class is memory corruption and the object may remain reachable after the erroneous free.

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

Patch: Revert "thermal/drivers/hwmon: Cleanup coding style a bit"
Commit: 2434f4765da8ccd7ef31be88b86f1bfa2e95be11
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2434f4765da8ccd7ef31be88b86f1bfa2e95be11

Commit description:

Revert commit 030a48b ("thermal/drivers/hwmon: Cleanup coding style
a bit") that introduced a use-after-free into the error path of
thermal_add_hwmon_sysfs() by removing a valid check from it.

Link: https://lore.kernel.org/linux-hwmon/20260803183915.4ED7D1F000E9@smtp.kernel.org/
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://patch.msgid.link/5123895.31r3eYUQgx@rafael.j.wysocki
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/thermal/thermal_hwmon.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=2434f4765da8ccd7ef31be88b86f1bfa2e95be11

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

The original Linux kernel CVE announcement for CVE-2026-74604 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74604

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: 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: NO
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).