[CVE-2026-89626][MODERATE 7.0] HID: sensor: custom: Fix field sysfs group cleanup on failure

[CVE-2026-89626][MODERATE 7.0] HID: sensor: custom: Fix field sysfs group cleanup on failure

[AL-KERNEL]

CVE: CVE-2026-89626
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: HID: sensor: custom: Fix field sysfs group cleanup on failure
Commit: 79154fad98ee843e5363940841e2d831503c190a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=79154fad98ee843e5363940841e2d831503c190a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89626
Analysis date: Sat, 12 Sep 2026 01:40:29 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A partial sysfs setup failure in HID custom sensor handling can leave field attribute groups registered after sensor_inst fields is freed, creating a local stale sysfs object UAF that can cause kernel DoS and requires manual review for stronger memory safety impact.

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

The original Linux kernel CVE announcement for CVE-2026-89626 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89626

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-2026-89626	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89626 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-459;*CWE-416;*CWE-772;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A cleanup error in HID sensor custom sysfs setup can leave field attribute groups registered when hid_sensor_custom_add_attributes fails after creating some groups. Later failure handling can free sensor_inst fields while stale sysfs attributes still reference entries from that array, creating a use-after-free candidate and a likely kernel crash on later sysfs access. For the CVSS the PR:L is used because triggering and interacting with the affected sysfs state requires a local user or local process context, not a remote network packet. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality or integrity impact because stale sysfs callbacks can reference freed kernel memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	USB SIMPLEFIX  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

## 1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

No floor or cap changed the conservative score.
No floor or cap changed the paranoid score.

## 2. Signal breakdown

Conservative positive signals:

* +2 Real UAF / lifetime violation. Previously created sysfs groups could remain registered while `sensor_inst->fields` is later freed, leaving sysfs-visible objects pointing into freed storage.
* +1 Reliable kernel crash / strong DoS. Later sysfs access to stale field-backed attributes can plausibly dereference freed memory and crash the kernel.
* +1 Concrete persistent resource/reference leak. The already-created sysfs groups are not removed on partial failure, leaving kernel-visible registrations/references behind normal cleanup.

Paranoid additional signal:

* +1 Structured stale-object exploitation leverage. The stale objects are not only passive cleanup metadata. They are sysfs attribute groups reachable from userspace after partial setup failure, and later sysfs operations may consume freed field-backed structures. Controlled reclaim is not demonstrated, so this is not Class A.

Non-awarded signals:

* +0 Controlled reclaim not demonstrated.
* +0 Arbitrary or directed kernel write not demonstrated.
* +0 Confidentiality and integrity impact not directly awarded. The UAF can support paranoid CVSS concern, but ActionableScore does not assign C/I points without a concrete disclosure or write primitive.
* +0 Local unprivileged trigger not awarded because the complete trigger chain for forcing `sysfs_create_group()` failure after partial success is not established.
* +0 Remote reachability not established. This is not packet-triggered.
* +0 Race penalty not applied. This is an ordered partial-initialization error path, not a demonstrated hard timing race.
* +0 Physical or rare-hardware penalty not applied. HID sensor hardware is relevant, but the supplied evidence does not prove a physical-only or rare-hardware attacker prerequisite.
* +0 Concrete repeated release/refcount signal not awarded. The patch shows stale sysfs group references and freed backing storage, not a second lifetime/refcount mutation on the exact same dangling reference.
* +0 Extra availability not awarded because the crash/DoS is already counted once.

Repeated-release/refcount checklist:

* First release can end lifetime: `kfree(sensor_inst->fields)` can end the lifetime of the field array.
* Exact same reference survives to a second lifetime mutation: not established.
* Second operation mutates lifetime/refcount: not established.
* Dedicated +1 concrete repeated release/refcount: not awarded.
* Paranoid repeated-refcount leverage +1: not awarded.
* FLOOR 5 from repeated release/refcount: not applied.

## 3. Reachability analysis

The vulnerable path is in HID custom sensor initialization. It is reached when `hid_sensor_custom_add_attributes()` creates sysfs groups for per-field attributes and a later `sysfs_create_group()` call fails after earlier groups have already been created.

A local actor may be able to interact with the resulting sysfs attributes if the broken partial state exists. However, the supplied patch does not prove that an ordinary local user can reliably cause the partial `sysfs_create_group()` failure or instantiate the needed HID sensor device without prior setup.

Host administrator privilege is therefore not positively established, but below-host-admin reachability is also not fully established.

* HostAdminRequired: UNKNOWN.
* NamespaceScopedPrivilege: NO. No namespace-scoped capability path is indicated.
* Prior host setup: likely depends on HID sensor device presence and driver probing, but the supplied evidence does not prove a mandatory host-admin-only setup step.
* Network trigger: none.
* Race repeatability: not a race. The difficult part is forcing or reaching the partial sysfs setup failure state.

## 4. Primitive and severity interpretation

The exact primitive is a partial-initialization cleanup bug that can leave sysfs attribute groups registered after their backing `sensor_inst->fields` array is freed.

This is a real lifetime violation and UAF candidate because sysfs state can retain pointers into freed field storage. The stale storage is active structured kernel state rather than a fixed DMA buffer or one-shot cleanup-only pointer. It is exposed through sysfs attribute access, which makes the stale object surface more meaningful than a purely internal destructor fault.

This is still Class B, not Class A. The patch does not establish controlled reclaim, attacker-shaped replacement contents, arbitrary read/write, callback hijack, information disclosure, or demonstrated privilege escalation.

Demonstrated consequence is local kernel crash / DoS. Speculative consequence is stronger memory-safety impact if stale sysfs callbacks consume reclaimed memory in a useful way, but that requires manual source and call-site review.

ImportantCandidate=YES because an externally reachable stale sysfs object referencing freed kernel storage leaves meaningful exploitation leverage unresolved.

AutoDowngradeAllowed=NO because treating this as an ordinary cleanup leak could miss a real active-object UAF reachable through sysfs after failed initialization.

Likely operational severity is Actionable Moderate, with Important-class review justified if product exposure shows that non-admin local users can trigger the partial setup failure or access the stale attributes.

## 5. One-sentence report phrase

A partial sysfs setup failure in HID custom sensor handling can leave field attribute groups registered after sensor_inst fields is freed, creating a local stale sysfs object UAF that can cause kernel DoS and requires manual review for stronger memory safety impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch establishes stale sysfs-visible state backed by freed kernel memory, and the extent of post-free callback behavior and attacker reachability cannot be safely auto-downgraded from the small diff alone.

## 7. Call-site confidence

Call-site confidence: medium

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

Patch: HID: sensor: custom: Fix field sysfs group cleanup on failure
Commit: 79154fad98ee843e5363940841e2d831503c190a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=79154fad98ee843e5363940841e2d831503c190a

Commit description:

hid_sensor_custom_add_attributes() creates one sysfs group for each
custom sensor field. If sysfs_create_group() fails after some groups
have already been created, the function returns the error without
removing the previously created groups.

Add a local unwind path to remove the groups that were already created.
With enable_sensor exposed only after the field attributes are ready,
this path can free sensor_inst->fields without leaving enable_sensor
able to access pointers into that array.

Fixes: 4a7de05 ("HID: sensor: Custom and Generic sensor support")
Cc: stable@vger.kernel.org
Signed-off-by: Haoxiang Li <haoxiang_li2024@163.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/hid/hid-sensor-custom.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=79154fad98ee843e5363940841e2d831503c190a

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

The original Linux kernel CVE announcement for CVE-2026-89626 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89626

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: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).