[CVE-2026-80705][LOW] drm/amd/display: check if dml21_add_phantom_plane() is successful

[CVE-2026-80705][LOW] drm/amd/display: check if dml21_add_phantom_plane() is successful

[AL-KERNEL]

CVE: CVE-2026-80705
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/amd/display: check if dml21_add_phantom_plane() is successful
Commit: 062cfd6c678f6647c8841f684d6dadab08d95512
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=062cfd6c678f6647c8841f684d6dadab08d95512
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80705
Analysis date: Fri, 28 Aug 2026 05:21:54 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-80705 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80705

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: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-80705	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-252;**CWE-476;CWE-754;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference in the AMD display DML21 path can occur because dml21_handle_phantom_streams_planes() treated dml21_add_phantom_plane() as successful even when no phantom plane was allocated. A local user with access to DRM/KMS modesetting on affected AMD hardware may be able to trigger the faulty path through display configuration that uses SubVP phantom streams and planes, especially under allocation failure or unsupported state conditions. For the CVSS the PR:L is used because triggering generally requires local access to the graphics device or a user session with permission to issue DRM/KMS configuration changes, not full administrator privileges. The issue is not network reachable. Impact is denial of service via kernel crash or display stack crash only. No credible UAF, OOB write, or arbitrary write primitive is indicated by the patch context, so confidentiality and integrity are not raised.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)  SKIP CVE-2026-80705 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	DANGER SIMPLEFIX HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

======================================================================
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 logged-in local user with DRM/KMS modesetting access may be able to exercise display configuration paths on affected AMD hardware.
* Reliable kernel crash / strong DoS: +1. The commit explicitly says the missing allocation check can lead to a later segfault.
* Rare AND difficult-to-reach subsystem/configuration: -1. The path appears specific to AMD Display DML21 / DCN401 and SubVP phantom plane handling.
* Special runtime conditions: -1. Triggering likely depends on a particular display topology, SubVP use, allocation failure, or unsupported state.
* No memory corruption signal added. The patch supports NULL pointer dereference / missing allocation check, not UAF, OOB write, double free, type confusion, or page ownership corruption.
* No LPE signal added. There is no supported reclaim, overwrite, callback control, stale object reuse, or privilege boundary bypass.

3. Reachability analysis
A local user with access to DRM/KMS display configuration is the plausible attacker. This does not appear network reachable. Containers generally do not help unless the container is granted direct access to the relevant DRM device node. The bug is hardware and configuration dependent, and affected systems need AMD display hardware using the DML21 / DCN401 path with phantom plane handling.

4. Severity interpretation
This behaves like an ordinary Moderate or Low-like local DoS rather than an Important candidate. The theoretical impact is a kernel or display stack crash from a NULL pointer dereference. Realistic exploitation evidence does not show memory corruption beyond a missing object check, and does not support confidentiality, integrity, or privilege escalation impact.

5. One-sentence report phrase
AMD display DML21 can dereference a missing phantom plane after unchecked dml21_add_phantom_plane() failure, allowing a local DRM/KMS user on affected hardware to cause a DoS.

6. Manual review recommendation
NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED
Reason: local hardware-specific NULL pointer dereference DoS only, with no evidence of UAF, OOB write, ownership bypass, or privilege escalation.

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

Patch: drm/amd/display: check if dml21_add_phantom_plane() is successful
Commit: 062cfd6c678f6647c8841f684d6dadab08d95512
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=062cfd6c678f6647c8841f684d6dadab08d95512

Commit description:

Verify that the phantom plane was allocated to avoid a later
segfault.

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4970
Fixes: 70839da ("drm/amd/display: Add new DCN401 sources")
Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Fangzhi Zuo <jerry.zuo@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 5adb54a )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/display/dc/dml2_0/dml21/dml21_utils.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=062cfd6c678f6647c8841f684d6dadab08d95512

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

The original Linux kernel CVE announcement for CVE-2026-80705 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80705

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:L/UI:N/S:U/C:N/I:N/A:H
  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).