[CVE-2026-43243][LOW] drm/amd/display: Add signal type check for dcn401 get_phyd32clk_src [ Upstream

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

CVE: CVE-2026-43243
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/amd/display: Add signal type check for dcn401 get_phyd32clk_src [ Upstream
Commit: 23e7150afc70da615857f9f07b494ec58540f096
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=23e7150afc70da615857f9f07b494ec58540f096
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43243
Analysis date: Sat, 01 Aug 2026 12:58:16 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-43243 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43243

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-43243	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-754;CWE-703;BEST CVSS score: '5.5';DESCR 'A crash can occur in the AMD DCN401 display path because get_phyd32clk_src() may access link encoder state for a DPIA link where that state is not valid. The issue is triggered through local display configuration or hotplug and depends on affected AMD display hardware and a DPIA link path. For the CVSS the PR:L is used because reliable triggering generally requires a local user or display management process with access to DRM KMS modeset operations, or local control over display hotplug on the affected system. The issue is not network reachable. Impact is denial of service through a kernel crash. There is no clear evidence of an information leak, arbitrary write, UAF, or privilege escalation primitive in the provided patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)  SKIP CVE-2026-43243  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	DANGER HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2
ActionableScoreLower=1

1. ActionableScore
* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Local unprivileged trigger: +1. A local user or display-management process may be able to trigger modeset or hotplug related paths on affected AMD display hardware.
* Reliable kernel crash / strong DoS: +1. The commit explicitly says accessing link encoder state on a DPIA link can crash.
* Physical-only or rare hardware-only condition: -1 conservative. The issue depends on AMD DCN401 display hardware and a DPIA link path, so exposure is narrower than a common kernel interface.
* No remote reachable signal. This is not a network-triggerable path.
* No memory corruption signal. The patch indicates an invalid link encoder access / likely NULL dereference, not UAF, OOB write, type confusion, arbitrary write, or refcount corruption.
* No LPE signal. There is no demonstrated reclaim, overwrite, callback control, stale object reuse, or privilege escalation primitive.
* Call-site confidence: medium. The changed function context is visible, but broader display call paths are not fully included.

3. Reachability analysis
The likely trigger is local display configuration, modeset, or hotplug on systems with affected AMD DCN401 display hardware and a DPIA link. A normal local graphical user may have enough practical influence through DRM KMS depending on session permissions, but this is still local and hardware dependent. Containers usually do not get direct DRM KMS access unless the device is passed through. The path is not remotely reachable and is not a common networking or filesystem exposure.

4. Severity interpretation
This behaves like an ordinary Moderate or Low-like kernel DoS issue. The theoretical impact is a local kernel crash, but the patch does not support memory corruption, confidentiality impact, integrity impact, or privilege escalation. The paranoid score only avoids the hardware rarity deduction and keeps the issue as a local DoS, not an Important-class candidate.

5. One-sentence report phrase
A local AMD DCN401 display crash can occur because get_phyd32clk_src() may access invalid link encoder state for a DPIA link, causing denial of service without evidence of memory corruption or privilege escalation.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. The issue is local, hardware-specific, DoS-only, and the patch context does not indicate UAF, OOB write, type confusion, information leak, or a plausible LPE primitive.

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

Patch: drm/amd/display: Add signal type check for dcn401 get_phyd32clk_src [ Upstream
Commit: 23e7150afc70da615857f9f07b494ec58540f096
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=23e7150afc70da615857f9f07b494ec58540f096

Changed files:
  drivers/gpu/drm/amd/display/dc/hwss/dcn401/dcn401_hwseq.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=23e7150afc70da615857f9f07b494ec58540f096

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

The original Linux kernel CVE announcement for CVE-2026-43243 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43243

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 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: 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).