[CVE-2026-98998][LOW] drm/bridge: th1520-dw-hdmi: Fix remove() callback

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

CVE: CVE-2026-98998
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/bridge: th1520-dw-hdmi: Fix remove() callback
Commit: d7cd43c2f546170ed42b2498d13805f4f89193c1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d7cd43c2f546170ed42b2498d13805f4f89193c1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98998
Analysis date: Mon, 26 Oct 2026 15:02:47 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
TH1520 HDMI removal passes a wrapper object as the embedded DW-HDMI object, permitting wrong-offset teardown accesses and a likely local kernel crash on affected hardware.

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

The original Linux kernel CVE announcement for CVE-2026-98998 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98998

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-2026-98998	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98998 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=LOW RESULT=DIFF TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (final Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H';CWE-843;CWE-704;CWE-822;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.7';DESCR 'The TH1520 HDMI remove callback retrieved platform drvdata as struct dw_hdmi even though probe stored a struct th1520_hdmi pointer. Passing this wrongly typed pointer to dw_hdmi_remove can make teardown access fields at incorrect offsets and may cause invalid reads, invalid writes, corrupted DRM state, or a kernel crash. For the CVSS the PR:H value is selected because reliable triggering normally requires administrative control over device unbind, driver removal, or platform device teardown. The issue is local and is not reachable through HDMI input or ordinary display traffic. The demonstrated impact is availability loss, while the paranoid score accounts for potential kernel memory corruption from teardown operations on the wrong object. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 6.7 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage LOW to LOW 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 V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 2.0 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	SIMPLEFIX HARDWARE LINUS KPANIC_UNSUPPORTED_REMOVED V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED	-	-	checked

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

ActionableScore=1
ActionableScoreLower=0
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 0 (+1 wrong-type structured-pointer consumption, +1 plausible crash, -2 uncommon TH1520 hardware).
* Conservative score: 0.
* Raw paranoid score: 1 (base signals plus +1 for likely teardown mutation through fields read at incorrect offsets).
* Paranoid score: 1; no floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 weak/indirect corruption candidate: `platform_get_drvdata()` returns `struct th1520_hdmi *`, but vulnerable code passes it as `struct dw_hdmi *` to a nontrivial teardown helper.
* +1 reliable crash/DoS concern: wrong-offset teardown accesses plausibly produce an invalid dereference or corrupt DRM teardown state.
* -2 rare hardware dependency: the affected driver is specific to the TH1520 HDMI controller; this is a material platform prerequisite, not merely a generic DRM path.
* Paranoid +1: `dw_hdmi_remove()` is expected to consume and mutate structured teardown state, so wrong-offset writes are technically plausible. The supplied code does not establish their exact target or width.
* No real UAF, confirmed OOB write, controlled type confusion, attacker-selected payload, arbitrary write, disclosure, authorization bypass, or LPE is shown.
* The same crash was not counted again as a separate availability impact.

3. Reachability analysis

The callback is reached during platform-driver/device removal. Administrative sysfs unbind, module removal, or platform teardown is the grounded trigger model, but the supplied evidence does not prove that every complete trigger requires effective host-administrator power; therefore `HostAdminRequired=UNKNOWN`. Ordinary display traffic and HDMI input do not reach it. No namespace-scoped path is present, and no race is required. Compatible TH1520 hardware and an instantiated driver are prerequisites.

4. Primitive and severity reading

The primitive is a wrong-type active structured pointer passed to `dw_hdmi_remove()`, not stale storage or a UAF. The helper may read or mutate fields at incorrect offsets, but exact invalid writes and downstream consumers are not visible. This supports constrained CLASS_B review rather than CLASS_A. Shown risk is teardown failure or kernel crash; memory corruption beyond that remains plausible but unproven. The privileged teardown context and hardware specificity make Important severity unsupported, so automatic Moderate/Low-like downgrade remains permissible after review.

5. One-sentence report phrase

TH1520 HDMI removal passes a wrapper object as the embedded DW-HDMI object, permitting wrong-offset teardown accesses and a likely local kernel crash on affected hardware.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm `dw_hdmi_remove()` field accesses and whether any wrong-offset write occurs before an inevitable fault.

7. Call-site confidence

Call-site confidence: medium

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

Patch: drm/bridge: th1520-dw-hdmi: Fix remove() callback
Commit: d7cd43c2f546170ed42b2498d13805f4f89193c1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d7cd43c2f546170ed42b2498d13805f4f89193c1

Commit description:

This driver stores struct th1520_hdmi * in platform drvdata, but
th1520_dw_hdmi_remove() was reading it back as struct dw_hdmi *
and passing it to dw_hdmi_remove(), so teardown runs on the wrong
pointer.

Retrieve struct th1520_hdmi * from platform drvdata and pass
hdmi->dw_hdmi to dw_hdmi_remove().

Fixes: 96f30ee ("drm/bridge: add a driver for T-Head TH1520 HDMI controller")
Signed-off-by: Felix Gu <ustc.gu@gmail.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Cc: stable@vger.kernel.org
Signed-off-by: Icenowy Zheng <zhengxingda@iscas.ac.cn>
Link: https://patch.msgid.link/20260321-th1520-v1-2-ec877197770d@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/bridge/th1520-dw-hdmi.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=d7cd43c2f546170ed42b2498d13805f4f89193c1

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

The original Linux kernel CVE announcement for CVE-2026-98998 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98998

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:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.7

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: 0
  Paranoid ActionableScore: 1

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).