[CVE-2026-98197][MODERATE REGULAR] hwmon: (w83791d) remove fan/pwm 4-5 sysfs group on remove

[CVE-2026-98197][MODERATE REGULAR] hwmon: (w83791d) remove fan/pwm 4-5 sysfs group on remove

[AL-KERNEL]

CVE: CVE-2026-98197
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: hwmon: (w83791d) remove fan/pwm 4-5 sysfs group on remove
Commit: 081e3a78453635fb370b1712809d2af29e60b4c5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=081e3a78453635fb370b1712809d2af29e60b4c5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98197
Analysis date: Thu, 08 Oct 2026 14:18:54 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98197 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98197

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: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-98197	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98197 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (legacy and Aegis reconciliation differ; DECISION: legacy MODERATE vs Aegis 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-459;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'The optional fan and PWM 4 and 5 sysfs files can remain after the w83791d driver is unbound. Their callbacks continue to access driver data that is allocated with devm and released after unbind, creating a local use-after-free candidate. A local process may trigger stale reads or writes by accessing the remaining sysfs files after device teardown. The most direct impact is a kernel crash and denial of service. Access to reclaimed data may also cause limited information disclosure or corruption of a reused kernel object, while reliable privilege escalation is not established by the available code. For the CVSS the PR:L value is selected because a local user may access readable stale sysfs attributes after a legitimate privileged unbind, although the required teardown condition makes AC:H appropriate. The issue is not network reachable and requires the w83791d driver, suitable hardware, and creation of the optional fan and PWM sysfs group.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	MAYBE	SIMPLEFIX ERRORPATH HARDWARE LINUS  INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 4
* Paranoid score: 4
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 Real UAF. The optional sysfs callbacks remain reachable after the devm-managed `w83791d_data` lifetime ends.
* +1 Local unprivileged trigger. Readable hwmon attributes can plausibly invoke the stale callbacks after a separate privileged unbind, although exact permissions are not visible in the patch.
* +1 Realistic kernel crash. Callback access to released driver data can fault or operate on invalid mutex and cached device state.
* No structured stale-object leverage point. The callbacks use an active structured object, but controlled reclaim, replacement contents, useful pointer consumption, or callback control is not established.
* No attacker-influenced lifetime point. The attacker is not shown to control driver unbind or devm release.
* No confidentiality or integrity points. Readback of reclaimed bytes and useful modification of a replacement object are not established.
* No strong or weak LPE point. UAF existence alone is insufficient.
* No remote-reachability point. This is a local sysfs and device-lifecycle path.
* No race penalty. The stale files persist after teardown, so a narrow timing window is not required.
* No hardware penalty. Suitable hardware is required, but the supplied evidence does not establish that it is sufficiently rare for a numeric deduction.
* No extra availability point. The possible kernel crash is counted only once.
* No repeated-release/refcount signal. The patch shows stale callback access, not a second `put`, `free`, or refcount mutation on the same reference.
* Paranoid escalation was withheld because no additional technically established exploitation primitive exists.

3. Reachability analysis

The vulnerable state requires the optional fan and PWM 4 and 5 group to have been created, followed by driver unbind and release of devm-managed data. Driver unbind for a host I2C device is normally a host-management operation, but a separate local process may subsequently access any surviving readable sysfs files.

The evidence does not establish that one below-admin attacker can perform the complete creation, unbind, and stale-access sequence. It also does not establish that the attacker must personally hold host-admin privilege because legitimate administrative teardown can create the stale interface. Therefore `HostAdminRequired` is `UNKNOWN`.

The I2C device and driver binding are host-global rather than attacker-created namespace resources, so the complete operation is not namespace-scoped. No network trigger exists. This is not a race because the files remain present until another lifecycle event removes the device or its kobject.

4. Primitive and severity interpretation

The exact primitive is a persistent sysfs entry whose callbacks can dereference an active structured driver object after its devm-managed lifetime has ended. This is a real Class B UAF rather than a generic invalid-state warning.

The stale use occurs after normal teardown but is externally invoked through the surviving sysfs files. It is therefore broader than a dereference occurring only inside the remove function. Nevertheless, the supplied context establishes no controlled reclaim, attacker-shaped replacement object, directed kernel read or write, disclosure path, callback hijack, repeated lifetime mutation, or privilege-escalation chain.

A kernel crash is the defensible practical consequence. Stronger corruption is theoretically possible if the allocation is reused before callback execution, but useful exploitation of that reuse is not established. This keeps the issue below an Important candidate and permits automated Moderate handling, while manual review remains recommended because an actual post-lifetime callback path exists.

5. One-sentence report phrase

The w83791d driver can leave user-accessible fan and PWM sysfs callbacks active after their devm-managed driver data is released, creating a local use-after-free with a realistic kernel-crash consequence but no demonstrated controlled reclaim or privilege-escalation primitive.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm the attribute permissions and callback behavior, especially whether an unprivileged read performs mutex operations, updates cached fields, or returns data from reclaimed storage.

7. Call-site confidence

Call-site confidence: medium

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

Patch: hwmon: (w83791d) remove fan/pwm 4-5 sysfs group on remove
Commit: 081e3a78453635fb370b1712809d2af29e60b4c5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=081e3a78453635fb370b1712809d2af29e60b4c5

Commit description:

When the fan/pwm 4-5 pins are not used as GPIO, w83791d_probe()
creates the w83791d_group_fanpwm45 sysfs group on the I2C client
device.

The probe error path removes this group when a later initialization
step fails, but the normal remove path only removes w83791d_group.
As a result, the optional fan/pwm 4-5 sysfs files can remain after the
driver is unbound.

The callbacks associated with these files access the driver data,
which is devm allocated and released after driver unbind. Leaving the
sysfs files behind can therefore result in accesses to stale driver
data.

Remove w83791d_group_fanpwm45 during normal teardown as well.

This issue was found by manual code inspection.

Fixes: 6e1ecd9 ("hwmon: (w83791d) fan 4/5 pins can also be used for gpio")
Cc: stable@vger.kernel.org
Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
Link: https://patch.msgid.link/20260914062809.1650538-1-lgs201920130244@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/hwmon/w83791d.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=081e3a78453635fb370b1712809d2af29e60b4c5

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

The original Linux kernel CVE announcement for CVE-2026-98197 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98197

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: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: 4

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.
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).