[CVE-2026-89819][MODERATE REGULAR] drm/amd/display: validate plane degamma LUT size for private color prop

[CVE-2026-89819][MODERATE REGULAR] drm/amd/display: validate plane degamma LUT size for private color prop

[AL-KERNEL]

CVE: CVE-2026-89819
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amd/display: validate plane degamma LUT size for private color prop
Commit: f6f04d8ae5725bcc893bdc62e3467efd97255c5b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f6f04d8ae5725bcc893bdc62e3467efd97255c5b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89819
Analysis date: Wed, 16 Sep 2026 14:25:09 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89819 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89819

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.

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

CVE-2026-89819	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89819 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:L/I:N/A:H';CWE-125;CWE-369;*CWE-20;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.1';DESCR 'The AMD private plane degamma path accepts a user supplied LUT blob without first verifying that it contains MAX_COLOR_LUT_ENTRIES entries. A short blob can cause a divide by zero in __is_lut_linear or an out of bounds read when __drm_lut_to_dc_gamma processes a fixed number of entries regardless of the actual blob size. The most direct impact is a local kernel crash or disruption of the graphics stack. The out of bounds operation is read only in the analyzed path and no controlled write primitive is identified. For the CVSS the PR:L reflects that a local process must be able to access the DRM device and modify plane properties through DRM master, a DRM lease, or an equivalent graphics service context. The issue is not network reachable and requires a build that exposes AMD_PLANE_DEGAMMA_LUT through AMD_PRIVATE_COLOR. Confidentiality impact is rated L only in the paranoid score because adjacent kernel memory may be consumed by the color conversion path, although no reliable channel for returning that data to the caller is established. Privilege escalation is not demonstrated, but the concrete out of bounds read warrants manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)  SKIP CVE-2026-89819 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	OOB DANGER UAF HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

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

2. Signal breakdown

* +1 Reliable kernel crash / strong DoS. A malformed LUT can cause an in-kernel divide-by-zero, and the fixed-size conversion loop can read beyond the supplied blob.
* +0 Limited read-only OOB. The patch establishes an OOB read but no disclosure channel, subsequent write, callback influence, or security-sensitive value use.
* +0 Weak corruption concern. No independently useful corruption primitive is established.
* No local-unprivileged bonus was awarded because access to the complete private KMS plane-property operation by an ordinary user is not established.
* No privilege penalty was applied because host-admin-equivalent privilege is not positively established.
* No rare-configuration penalty was applied. AMD_PRIVATE_COLOR limits exposure, but the evidence does not establish that affected builds are both rare and difficult to reach.
* Controlled reclaim, arbitrary write, UAF, type confusion, information disclosure, privilege escalation, and remote reachability are not demonstrated.
* No extra Availability point was awarded because it would duplicate the same divide-by-zero or invalid-read failure.
* Confidentiality was not awarded merely because an internal OOB read exists. No path returning adjacent bytes to userspace, the network, or another observable output is established.

3. Reachability analysis

The attacker must submit an invalid AMD_PLANE_DEGAMMA_LUT blob through the DRM/KMS plane-property interface on an AMDGPU build with AMD_PRIVATE_COLOR enabled. The operation would normally be performed by a DRM master, compositor, display server, DRM lessee, or delegated graphics service rather than arbitrary code that can merely open a render node.

The supplied evidence does not establish whether an ordinary logged-in user can obtain the exact KMS authority needed for this property in the evaluated deployment. It also does not establish that host administration is required. HostAdminRequired is therefore UNKNOWN.

No user-namespace or network-namespace capability governs this display-control path, so NamespaceScopedPrivilege is NO. No network trigger, timing race, special physical access, or attacker-controlled lifetime transition is involved. AMD GPU support and AMD_PRIVATE_COLOR are prerequisites.

4. Primitive and severity interpretation

The exact primitives are a divide-by-zero and a read beyond the end of a user-supplied DRM property blob. This is not a UAF, ownership violation, repeated release, active-state retirement failure, or write primitive.

The OOB operation is read-only in the demonstrated path. The conversion routine may consume adjacent kernel memory as color data, but no reliable disclosure path or security-sensitive control effect is shown. The practical patch-supported consequence is an Oops, kernel crash, or disruption of the graphics stack.

PrimitiveClass is CLASS_C because the demonstrated behavior is invalid input causing a fault or limited invalid read without an independently useful corruption primitive. ImportantCandidate is NO because there is no write, disclosure, lifetime corruption, authorization bypass, or plausible privilege-escalation mechanism. AutoDowngradeAllowed is YES because no unresolved Important-preserving primitive is established.

5. One-sentence report phrase

A malformed private AMD plane degamma LUT can cause an in-kernel divide-by-zero or limited out-of-bounds read, with crash or graphics disruption as the demonstrated impact and no established disclosure, write, or privilege-escalation primitive.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm the deployment-specific DRM master or lease boundary and whether converted OOB data can become observable, but the current evidence does not justify Important-class treatment.

7. Call-site confidence

Call-site confidence: medium

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

Patch: drm/amd/display: validate plane degamma LUT size for private color prop
Commit: f6f04d8ae5725bcc893bdc62e3467efd97255c5b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f6f04d8ae5725bcc893bdc62e3467efd97255c5b

Commit description:

Unlike the CRTC degamma path, which is guarded by
amdgpu_dm_verify_lut_sizes(), the per-plane degamma LUT size was never
validated before use. __set_dm_plane_degamma() passed the user-supplied
size straight into __is_lut_linear() and, for a non-linear LUT, into
__set_input_tf() -> __drm_lut_to_dc_gamma(), the latter always iterating
MAX_COLOR_LUT_ENTRIES entries regardless of the actual LUT size.

A malformed AMD_PLANE_DEGAMMA_LUT blob (e.g. a single entry) could thus
trigger a divide-by-zero in __is_lut_linear() or an out-of-bounds read in
__drm_lut_to_dc_gamma(). Reject any plane degamma LUT whose size does not
match MAX_COLOR_LUT_ENTRIES, mirroring the invariant the code already
asserts a few lines below (and which the CRTC path enforces).

The AMD_PLANE_DEGAMMA_LUT property is only exposed on builds with
AMD_PRIVATE_COLOR defined.

Fixes: 980f871 ("drm/amd/display: add plane degamma TF and LUT support")
Cc: stable@vger.kernel.org
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Melissa Wen <mwen@igalia.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.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=f6f04d8ae5725bcc893bdc62e3467efd97255c5b

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

The original Linux kernel CVE announcement for CVE-2026-89819 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89819

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: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:L/I:N/A:H
  The Best / paranoid CVSS score: 6.1

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: 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: 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).