[CVE-2026-63843][LOW] drm/amdgpu/jpeg: set no_user_fence for JPEG v4.0.5 ring [ Upstream

[CVE-2026-63843][LOW] drm/amdgpu/jpeg: set no_user_fence for JPEG v4.0.5 ring [ Upstream

[AL-KERNEL]

CVE: CVE-2026-63843
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/amdgpu/jpeg: set no_user_fence for JPEG v4.0.5 ring [ Upstream
Commit: 424510b60d4698a75a6ff71acdd88b528f0f39af
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=424510b60d4698a75a6ff71acdd88b528f0f39af
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63843
Analysis date: Sun, 19 Jul 2026 11:42:41 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-63843 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63843

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-2026-63843	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	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-20;CWE-754;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'AMDGPU JPEG v4.0.5 rings do not support 64-bit user fence writes, but CS submissions with user fences were not rejected for this ring. A local process with access to the DRM render device could submit a JPEG command stream with a user fence and reach unsupported fence handling. For the CVSS the PR:L is used because practical triggering requires local code execution with access to the GPU device node, which is commonly available to users in the render or video group. The issue is not network reachable and does not provide a demonstrated kernel memory corruption primitive. Impact is denial of service, typically a failed job, GPU hang, or GPU reset affecting graphics or compute availability.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)  SKIP CVE-2026-63843 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	SIMPLEFIX HARDWARE  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2

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

2. **Signal breakdown**
* Local unprivileged trigger: +1. A local process with access to the AMDGPU DRM render node can typically submit CS jobs.
* Availability impact realistic: +1. Unsupported user-fence handling on this JPEG ring can plausibly cause failed jobs, GPU hangs, or GPU reset.
* No memory corruption signal: +0. The patch only sets `no_user_fence = true` and does not show UAF, OOB access, double-free, stale pointer reuse, arbitrary write, or type confusion.
* No privilege escalation signal: +0. There is no demonstrated LPE primitive.
* No network reachability: +0. This is a local DRM/GPU submission path.
* Device API high-control bonus not applied: +0. The patch does not show attacker control over object lifetime, refcounts, DMA mappings, page ownership, or callback targets.
* Validation-only cap applies conceptually. This is an input rejection fix for unsupported user-fence submissions.

Call-site confidence: medium. The patch only changes a ring capability flag, but AMDGPU `no_user_fence` semantics are clear enough to classify this as rejection of unsupported CS submissions.

3. **Reachability analysis**
A local user or process with access to the DRM render device can potentially trigger the issue by submitting a JPEG CS with a user fence. In many desktop or GPU compute deployments, render-node access is available to users in GPU-related groups, so PR:L is a reasonable practical interpretation. Containers may inherit GPU device access if explicitly passed through, but this is not usually exposed by default. The affected path is hardware and driver specific to AMDGPU JPEG v4.0.5, and it is not remotely reachable over the network.

4. **Severity interpretation**
This behaves like an ordinary Moderate or Low-like local device DoS. The realistic impact is GPU job failure, GPU hang, or GPU reset. The patch does not support classifying this as memory corruption or privilege escalation. Theoretical concern is limited because the change is a capability validation flag rather than a fix for a concrete corruption sink.

5. **One-sentence report phrase**
AMDGPU JPEG v4.0.5 did not reject unsupported 64-bit user-fence CS submissions, allowing a local GPU user to trigger likely GPU job failure or reset, with no demonstrated kernel memory corruption or privilege escalation primitive.

6. **Manual review recommendation**
NO MANUAL CHECK NEEDED

This can be auto-closed or handled as low-priority Moderate unless additional vendor information shows a concrete kernel crash, memory corruption primitive, or privilege escalation path.

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

Patch: drm/amdgpu/jpeg: set no_user_fence for JPEG v4.0.5 ring [ Upstream
Commit: 424510b60d4698a75a6ff71acdd88b528f0f39af
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=424510b60d4698a75a6ff71acdd88b528f0f39af

Changed files:
  drivers/gpu/drm/amd/amdgpu/jpeg_v4_0_5.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=424510b60d4698a75a6ff71acdd88b528f0f39af

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

The original Linux kernel CVE announcement for CVE-2026-63843 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63843

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:L
  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: unknown
  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).