[CVE-2026-98781][LOW] drm/mediatek: Fix pdev reference leak in mtk_drm_bind()

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

CVE: CVE-2026-98781
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/mediatek: Fix pdev reference leak in mtk_drm_bind()
Commit: 4a8f9cad0fced77b36b297c67c42730c9cb32ec6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4a8f9cad0fced77b36b297c67c42730c9cb32ec6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98781
Analysis date: Sat, 24 Oct 2026 10:53:06 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A non-master MediaTek DRM bind path leaked one platform-device reference, with no demonstrated memory corruption, authorization bypass, or attacker-controlled resource exhaustion.

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

The original Linux kernel CVE announcement for CVE-2026-98781 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98781

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: LOW
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-2026-98781	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98781 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=0 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both LOW)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';*CWE-772;*CWE-401;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '2.3';DESCR 'The non-master path in mtk_drm_bind retained a reference obtained for the display mutex platform device and returned lacking the matching put_device call. The demonstrated primitive is a persistent device reference leak rather than memory corruption, UAF, information disclosure, or an immediate kernel crash. Reliable accumulation appears to require a matching multi mmsys hardware configuration and repeated driver bind or probe activity. For the CVSS the PR:H value is used because controlling the platform driver lifecycle normally requires administrative privileges. The issue is local and is not directly reachable through network traffic. Availability impact is low unless repeated privileged operations can accumulate enough retained resources to cause operational degradation. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 2.3 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. 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. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 0 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	MAYBE	SIMPLEFIX LEAK HARDWARE LINUS 	-	-	checked

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

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

1. ActionableScore

* Raw base score: 0 (+1 concrete persistent device-reference leak; -1 specialized multi-mmsys hardware path not ordinarily attacker-instantiable).
* Conservative score: 0. No floor or cap applies.
* Raw paranoid score: 0, with no technically supported stronger consequence.
* Paranoid score: 0.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 — `of_find_device_by_node()` acquires a reference to `private->mutex_dev`; the non-master early return omitted the matching `put_device()`, producing a concrete persistent reference leak.
* -1 — The path requires a MediaTek multi-mmsys configuration and non-master bind processing; an attacker cannot ordinarily instantiate this hardware topology.
* No UAF, OOB access, repeated release, memory overwrite, authorization bypass, disclosure, or immediate crash is shown.
* No strong DoS point: repeated bind/probe cycles and material resource accumulation are not demonstrated as attacker-controllable.
* B5-R and B3-PENDING do not apply: there is neither an OOB write nor a shared-backing write.

3. Reachability analysis

The leak occurs during platform-driver component binding, not through a shown DRM render-node ioctl or ordinary userspace operation. Repeated driver lifecycle control would normally involve host device-management authority, but the supplied evidence does not positively establish the complete trigger credentials; therefore `HostAdminRequired` and host UID 0 requirements remain unknown. The operation is host-global rather than namespace-scoped. No race is involved.

4. Primitive and severity reading

The exact defect is a missing reference release on an early-success path. It extends the platform-device reference lifetime but does not create a dangling pointer or consume freed storage. The shown consequence is one leaked device reference per qualifying bind; exhaustion or host-wide degradation requires unproven repetition. This is constrained Class C resource-management behavior, not an Important-grade corruption primitive. Auto-downgrade is allowed because no material unknown exploit or trust-boundary primitive remains.

5. One-sentence report phrase

A non-master MediaTek DRM bind path leaked one platform-device reference, with no demonstrated memory corruption, authorization bypass, or attacker-controlled resource exhaustion.

6. Manual review advice

NO MANUAL CHECK NEEDED

The patch establishes only a hardware-specific reference leak with no grounded security escalation path.

7. Call-site confidence

Call-site confidence: high

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

Patch: drm/mediatek: Fix pdev reference leak in mtk_drm_bind()
Commit: 4a8f9cad0fced77b36b297c67c42730c9cb32ec6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4a8f9cad0fced77b36b297c67c42730c9cb32ec6

Commit description:

When the device is not the mmsys master, mtk_drm_bind() returns early
after taking a reference on the disp-mutex device via
of_find_device_by_node(), without ever dropping it: mtk_drm_unbind()
only puts mutex_dev for the master. Drop the reference before returning
from the non-master path.

Fixes: 1ef7ed4 ("drm/mediatek: Modify mediatek-drm for mt8195 multi mmsys support")
Cc: stable@vger.kernel.org
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20260916174058.2088709-1-vulab@iscas.ac.cn/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/mediatek/mtk_drm_drv.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=4a8f9cad0fced77b36b297c67c42730c9cb32ec6

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

The original Linux kernel CVE announcement for CVE-2026-98781 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98781

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:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 2.3

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).