[CVE-2026-98860][MODERATE REGULAR] HID: bpf: cast size to ssize_t when checking hid_bpf_hw_request

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

CVE: CVE-2026-98860
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: HID: bpf: cast size to ssize_t when checking hid_bpf_hw_request
Commit: 8b85ef0f561039e249c3f883c5280a1449c6dbee
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8b85ef0f561039e249c3f883c5280a1449c6dbee
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98860
Analysis date: Mon, 19 Oct 2026 06:02:42 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A signed and unsigned comparison in hid_bpf_hw_request can convert a negative HID transport error into success and return stale or unchanged buffer data to a HID BPF program, but the supplied code establishes no OOB access, UAF, kernel crash, authorization bypass, or privilege escalation primitive.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98860 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98860

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-98860	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98860 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE RESULT=DIFF V39_AEGIS_ONE_STEP_UP=LOW->MODERATE TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (final Legacy and Aegis differ; FINAL: MODERATE, 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:L/I:L/A:L';CWE-195;CWE-681;CWE-391;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:L';BEST CVSS score: '4.5';DESCR 'A signed and unsigned comparison in hid_bpf_hw_request can convert a negative HID transport error such as EPIPE into a successful positive return value. The function can then copy the unchanged DMA request buffer back and allow a HID BPF program to process stale or potentially uninitialized data as a valid hardware response. No out of bounds access, UAF, arbitrary write, or direct kernel crash primitive is demonstrated because the copied length remains limited by size. For the CVSS the PR:L value is used in the paranoid score because some systems may delegate HID BPF management to a restricted service, container, or capability based user rather than require unrestricted root access. Triggering also depends on reaching the HID BPF request path while the transport driver returns a hardware error, so AC:H is appropriate. The issue is not network reachable. Impact is limited confidentiality and integrity risk within the HID BPF data path and possible disruption of the affected HID device. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 4.5 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE to LOW because the ActionableScore threshold rule was applied. final reconciliation stage LOW to MODERATE because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 and KPANIC_UNSUPPORTED_REMOVED and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 0 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	MAYBE	OOB USB BPF SIMPLEFIX HARDWARE LINUS MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 KPANIC_UNSUPPORTED_REMOVED V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* No floor or cap changed either score.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +0 invalid-state behavior. A negative transport error is converted into success, causing stale or unchanged data to be treated as a valid response.
* +0 weak corruption concern. The visible `memcpy()` remains bounded by `size`; no OOB read/write, UAF, arbitrary write, or kernel-object corruption is established.
* +0 confidentiality. Potentially uninitialized data is mentioned, but no protected kernel data disclosure path to userspace, network, or another principal is shown.
* +0 integrity. Incorrect HID/BPF behavior is plausible, but unauthorized modification of protected kernel state or another principal’s data is not established.
* +0 availability. Device or BPF-program disruption is possible, but no kernel crash, host-wide DoS, or persistent device failure is demonstrated.
* +0 authorization bypass. This is error-code mishandling, not a DENY-to-ALLOW security decision.
* No remote-reachability, local-unprivileged, controlled-reclaim, strong semantic-reinterpretation, or security-boundary bonuses apply.
* B5-R does not apply because there is no retry-accumulated heap OOB write.
* B3-PENDING does not apply because no shared-backing write is established.
* V33 and V32 do not apply because no attacker-corrupted active structured state or checksum metadata exists.
* B4-PENDING does not apply because no mandatory authorization guard is omitted.

3. Reachability analysis

The vulnerable path requires execution of `hid_bpf_hw_request()` and a HID transport driver returning a negative hardware error such as `-EPIPE`. The supplied evidence does not establish whether the complete HID BPF load, attachment, device access, and trigger sequence is available below host-admin-equivalent privilege. Therefore `HostAdminRequired` and `RequiresHostUID0` remain `UNKNOWN`.

No evidence establishes that all required BPF and HID operations are available through attacker-created user or network namespaces, so `NamespaceScopedPrivilege=UNKNOWN`. No direct network trigger exists. A physical or malfunctioning HID transport may help produce the error, but attacker control over that condition is not demonstrated. This is not a race.

4. Primitive and severity interpretation

The exact defect is a signed-versus-unsigned comparison. A negative `ssize_t` return value is promoted during comparison with `size_t`, appears larger than `size`, and is replaced with a successful positive length. The subsequent bounded copy returns unchanged, stale, or potentially uninitialized request-buffer data as though the hardware transaction succeeded.

This is Class C invalid-state behavior. It is not an active-object lifetime violation, UAF, repeated release, OOB access, or confirmed information leak. The demonstrated consequence is incorrect data consumption by a HID BPF program. Device misbehavior is plausible, while kernel crash, privilege escalation, protected-state corruption, and cross-boundary disclosure remain unsupported.

`ImportantCandidate=NO` because no meaningful corruption, authorization, ownership, or security-boundary primitive is established. `AutoDowngradeAllowed=YES` because the issue remains a bounded error-propagation defect without unresolved Important-grade leverage.

5. One-sentence report phrase

A signed and unsigned comparison in hid_bpf_hw_request can convert a negative HID transport error into success and return stale or unchanged buffer data to a HID BPF program, but the supplied code establishes no OOB access, UAF, kernel crash, authorization bypass, or privilege escalation primitive.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a bounded return-value handling bug with no concrete memory corruption, protected-resource impact, network exposure, or authorization boundary bypass.

7. Call-site confidence

Call-site confidence: medium

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UPSTREAM PATCH SUMMARY
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Patch: HID: bpf: cast size to ssize_t when checking hid_bpf_hw_request
Commit: 8b85ef0f561039e249c3f883c5280a1449c6dbee
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8b85ef0f561039e249c3f883c5280a1449c6dbee

Commit description:

As reported by Sashiko:
If a transport driver encounters a hardware error and returns a negative
error code such as -EPIPE, ret is implicitly promoted to size_t when
compared against size. This causes the negative error code to evaluate
as a large positive number, making the (ret > size) condition true.

This silently converts the hardware error into a success return value
and copies the unmodified buffer back, which could leave BPF programs
operating on uninitialized or stale data.

Fix this by casting size into ssize_t to return the actual negative
error code.

Link: https://lore.kernel.org/all/20260904130354.A79471F00A3D@smtp.kernel.org/
Fixes: 2b658c1 ("HID: bpf: prevent buffer overflow in hid_hw_request")
Cc: stable@vger.kernel.org
Acked-by: Jiri Kosina <jkosina@suse.com>
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/hid/bpf/hid_bpf_dispatch.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=8b85ef0f561039e249c3f883c5280a1449c6dbee

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

The original Linux kernel CVE announcement for CVE-2026-98860 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98860

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:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L
  The Best / paranoid CVSS score: 4.5

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: 0

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).