[CVE-2026-98669][MODERATE REGULAR] iio: buffer: serialize buffer teardown with mode claims

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

CVE: CVE-2026-98669
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: iio: buffer: serialize buffer teardown with mode claims
Commit: 89f3852a28fcf7bab599280cb082baa0675536db
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=89f3852a28fcf7bab599280cb082baa0675536db
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98669
Analysis date: Mon, 19 Oct 2026 02:36:31 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A race allowed IIO device unregister to invalidate active buffer state while a buffer-mode claim was held, potentially causing incorrect state consumption or a kernel crash, but no concrete UAF, write primitive, or privilege boundary bypass is established.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98669 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98669

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
======================================================================

CVE-2026-98669	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98669 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE AEGIS_AS=0 LEGACY=MODERATE RESULT=SAME V39_AEGIS_ONE_STEP_UP=LOW->MODERATE (final reconciliation agrees; DECISION: both 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:L/I:L/A:H';CWE-362;CWE-667;*CWE-664;*CWE-416;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A race exists between an IIO buffer mode claim and device unregister because iio_disable_all_buffers() can disable and deactivate buffers without taking mlock. A caller holding a buffer mode claim may therefore continue under the assumption that buffer state is stable while unregister invalidates state such as active_scan_mask. This can expose stale or invalid buffer state and may result in incorrect driver behavior or a kernel crash. For the CVSS the PR:L value is used for the paranoid score because a local process with access to an exposed IIO device or a delegated device context may participate in the race, although reliable device unregister normally requires higher privileges or physical hot removal. The race requires a timing window, so AC:H is appropriate. The issue is not network reachable. Impact is at least local denial of service, while limited confidentiality or integrity impact remains plausible if the invalidated state becomes a stale memory reference and should be reviewed manually. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.8 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were 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 KPANIC_UNSUPPORTED_REMOVED and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.0 and ActionableScore 0 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE. 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 2)	MAYBE	SIMPLEFIX HARDWARE LINUS KPANIC_UNSUPPORTED_REMOVED V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Conservative signals:

* +1 weak or indirect corruption candidate. Buffer teardown can invalidate active structured state, including `active_scan_mask`, while a claimant is entitled to treat that state as stable.
* No negative race penalty. A concurrent claim and unregister are required, but the evidence does not establish that the timing window is exceptionally narrow or difficult to repeat.

Paranoid signal:

* +1 potential kernel crash or strong DoS. A claimant may consume invalidated buffer state after concurrent disable or deactivation. This is technically plausible, but no concrete crashing dereference is shown in the supplied code.

Important non-awarded signals:

* Real UAF was not awarded because no allocation is shown to be freed and subsequently accessed.
* No OOB write, arbitrary write, controlled reclaim, repeated release, callback control, or information disclosure is established.
* Structured stale-object leverage was not awarded because the later operation consuming `active_scan_mask` is not supplied.
* Attacker-influenced active-state control was not awarded because no attacker-controlled state, replacement, or complete trigger sequence is established.
* V33 does not apply because no concrete attacker-controlled write, privileged downstream consumer, and trust boundary are jointly established.
* B5-R and B3-PENDING do not apply because there is no confirmed write outside an allocation or into shared backing.
* B4-PENDING does not apply because this is not an authorization decision defect.
* Remote reachability and namespace crossing are not established.
* Confidentiality and integrity points were not awarded from the prior speculative CVSS assessment.

3. Reachability analysis

The race requires one context to hold an IIO buffer-mode claim while `iio_device_unregister()` disables and deactivates the same buffers. The claim APIs are kernel interfaces used by IIO code or drivers, not a directly demonstrated unprivileged userspace interface.

Device unregister may be caused by administrative driver removal, device teardown, or physical hot removal. The supplied evidence does not establish which actor can drive both sides of the complete race. Therefore host-administrator privilege is neither positively required nor positively excluded.

No namespace-scoped capability check or delegated interface is shown. Prior availability of a relevant IIO device and driver is required, but there is insufficient evidence to classify the hardware as rare. Race repeatability and ordinary-user influence remain unresolved.

4. Primitive and severity interpretation

The exact primitive is a synchronization and active-state consistency violation. A mode claim holds `mlock` to preserve buffer mode and associated state, but unregister previously bypassed that lock and could disable or deactivate the buffers concurrently.

The affected state is active and structured, but the evidence establishes invalidation rather than post-lifetime use. There is no confirmed free followed by dereference, so `RealUAF=NO`. There is also no concrete second release or refcount mutation.

The demonstrated consequence is violation of the mode-claim lifetime guarantee and possible observation of invalid buffer state. A kernel fault is a defensible worst-case hypothesis, but the specific stale dereference and resulting panic are not shown. Limited confidentiality, integrity impact, privilege escalation, and trust-boundary crossing remain unsupported.

This is therefore CLASS_C rather than CLASS_B or CLASS_A. `ImportantCandidate=NO` because no independently useful corruption or boundary primitive is established. `AutoDowngradeAllowed=YES` because the current evidence supports an invalid-state or possible DoS issue, although targeted manual review of claim users is still advisable.

5. One-sentence report phrase

A race allowed IIO device unregister to invalidate active buffer state while a buffer-mode claim was held, potentially causing incorrect state consumption or a kernel crash, but no concrete UAF, write primitive, or privilege boundary bypass is established.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Inspect callers of `iio_device_claim_buffer_mode()` to determine whether they dereference `active_scan_mask` or other deactivated buffer objects after concurrent unregister and whether an actor below host administrator can drive the complete race.

7. Call-site confidence

Call-site confidence: medium

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

Patch: iio: buffer: serialize buffer teardown with mode claims
Commit: 89f3852a28fcf7bab599280cb082baa0675536db
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=89f3852a28fcf7bab599280cb082baa0675536db

Commit description:

Buffer-mode claims hold mlock to guarantee that the device remains in
buffer mode until the claim is released. Normal buffer updates take
info_exist_lock followed by mlock in iio_update_buffers().

However, iio_device_unregister() disables and deactivates all buffers
without taking mlock. This can invalidate buffer state, including
active_scan_mask, while a buffer-mode claim is held.

Take mlock in iio_disable_all_buffers() so that unregister honors the
mode-claim lifetime guarantee. The info_exist_lock -> mlock ordering
matches iio_update_buffers().

Fixes: 0a85654 ("iio: core: introduce iio_device_{claim|release}_buffer_mode() APIs")
Suggested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Jinseob Kim <kimjinseob88@gmail.com>
Reviewed-by: Joshua Crofts <joshua.crofts1@gmail.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/iio/industrialio-buffer.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=89f3852a28fcf7bab599280cb082baa0675536db

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

The original Linux kernel CVE announcement for CVE-2026-98669 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98669

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 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).