[CVE-2026-68106][MODERATE REGULAR] drm/amdgpu: fix division by zero with invalid uvd dimensions

[CVE-2026-68106][MODERATE REGULAR] drm/amdgpu: fix division by zero with invalid uvd dimensions

[AL-KERNEL]

CVE: CVE-2026-68106
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amdgpu: fix division by zero with invalid uvd dimensions
Commit: 52f9a588296432accf2982f7d258192a37562f4f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=52f9a588296432accf2982f7d258192a37562f4f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68106
Analysis date: Mon, 10 Aug 2026 09:57:23 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline ordinary Moderate. Manual review recommended due local render node DoS exposure
Manual review required: YES

Summary:
A local user with access to AMDGPU UVD decode submission can provide invalid H264 dimensions below 16 and trigger a kernel division by zero, causing denial of service without evidence of memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-68106 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68106

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: YES

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-2026-68106	MODERATE	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-369;*CWE-20;CWE-754;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 UVD decode handling can divide by zero when a submitted H264 decode message uses invalid dimensions with width below 16 or height below 16. These values make the macroblock counts zero and later calculations of DPB buffer count can fault in kernel context. For the CVSS the PR:L is used because a local user or process must be able to submit AMDGPU UVD decode commands through the DRM device interface, which is commonly exposed to users with render node access. The issue is not network reachable and requires local interaction with the GPU driver control path. Impact is denial of service. Base impact is C:N/I:N/A:L because the visible primitive is a division-by-zero fault without memory corruption. Paranoid impact is C:N/I:N/A:H because repeated malformed submissions may cause a kernel oops or system crash depending on kernel policy and driver state.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline ordinary Moderate. Manual review recommended due local render node DoS exposure (with actual score 3)  SKIP CVE-2026-68106 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	WARNONLY SIMPLEFIX HARDWARE  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline ordinary Moderate. Manual review recommended due local render node DoS exposure**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local process with access to the AMDGPU DRM render node may be able to submit malformed UVD H264 decode commands.

* Reliable kernel crash / strong DoS: +1
  The patch explicitly prevents a division by zero in kernel decode handling. This is a concrete fault condition, not merely a warning.

* Availability impact realistic: +1 in paranoid score only
  If the affected path is reachable through a render node and the divide-by-zero results in repeated kernel oops or panic depending on kernel policy, availability impact may be system-relevant. This is not counted in the lower score to avoid double-counting crash impact.

Not applied:

* No generic memory corruption. The patch shows division by zero, not UAF, OOB write, double free, refcount misuse, or type confusion.
* No LPE signal. There is no supported privilege escalation primitive.
* No confidentiality or integrity impact. No readback, data corruption, arbitrary write, or object lifetime issue is shown.
* No remote/network signal. This is a local GPU driver command submission path.
* No high-control API bonus. DRM/GPU ioctl access alone is not enough without evidence of attacker-controlled memory layout, lifetime, DMA ownership, callback, or refcount influence.

## 3. Reachability analysis

A local user or process that can submit AMDGPU UVD decode work through the DRM interface can potentially trigger the bug by using invalid dimensions below 16. On many systems, render nodes are available to non-root users in the video or render group, so PR:L is the practical assumption. Containers may matter if the GPU device node is passed through, but without device access the bug is not reachable. The path is not network reachable and depends on AMDGPU hardware and UVD decode support being present and accessible.

Call-site confidence: medium. The vulnerable function and validation point are visible, but the full ioctl submission path is not included in the provided patch.

## 4. Severity interpretation

This behaves like an ordinary to borderline actionable Moderate local DoS. The realistic impact is a kernel divide-by-zero fault from malformed decode parameters. Theoretical memory corruption or privilege escalation is not supported by the patch. The paranoid score is raised only for repeatable availability impact through commonly exposed render-node access, not for C/I impact.

## 5. One-sentence report phrase

A local user with access to AMDGPU UVD decode submission can provide invalid H264 dimensions below 16 and trigger a kernel division by zero, causing denial of service without evidence of memory corruption or privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the bug is not Important-class based on the patch alone, but local render-node exposure can make the DoS reachable by non-root users on affected AMDGPU systems.

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

Patch: drm/amdgpu: fix division by zero with invalid uvd dimensions
Commit: 52f9a588296432accf2982f7d258192a37562f4f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=52f9a588296432accf2982f7d258192a37562f4f

Commit description:

When width or height is less than 16, width_in_mb or height_in_mb
becomes 0, leading to fs_in_mb being 0. This causes a division by
zero when calculating num_dpb_buffer in H264 and H264 Perf decode
paths.

Add validation to reject frames with width < 16 or height < 16
before performing any calculations that depend on these values.

V2: Format change - move up all vaiable definitions.
V3: Use warn_once to avoid spam.

Signed-off-by: Boyuan Zhang <boyuan.zhang@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 3e41d26 )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/amdgpu/amdgpu_uvd.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=52f9a588296432accf2982f7d258192a37562f4f

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

The original Linux kernel CVE announcement for CVE-2026-68106 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68106

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: 2
  Paranoid ActionableScore: 3

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).