[CVE-2026-43400][MODERATE REGULAR] drm/amdgpu: add upper bound check on user inputs in signal ioctl

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

CVE: CVE-2026-43400
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amdgpu: add upper bound check on user inputs in signal ioctl
Commit: 6fff5204d8aa26b1be50b6427f833bd3e8899c4f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6fff5204d8aa26b1be50b6427f833bd3e8899c4f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43400
Analysis date: Sat, 01 Aug 2026 12:12:08 -0400
ActionableScore: 3
ActionableScore lower bound: 2
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-2026-43400 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43400

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-43400	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-400;CWE-789;CWE-770;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_userq_signal_ioctl accepted user supplied handle counts without an upper bound and used those counts to size memdup_user allocations for syncobj and BO handle arrays. A local process with access to the AMDGPU DRM device could pass very large counts and force excessive kernel memory allocation, causing memory pressure or an out of memory condition. For the CVSS the PR:L is used because reliable triggering requires local code execution with access to the DRM device node, but not full administrative privileges. The issue is not network reachable and does not provide a concrete memory corruption primitive. Impact is denial of service through resource exhaustion, with no supported confidentiality or integrity impact from the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 3) 	MAYBE	SIMPLEFIX HARDWARE MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=2

1. ActionableScore
* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Local unprivileged trigger: +1. A local process with access to the AMDGPU DRM device node can call amdgpu_userq_signal_ioctl. This is PR:L rather than PR:H in typical desktop or GPU compute setups where render device access may be delegated.
* Reliable kernel crash / strong DoS: +1. The commit explicitly says huge input values can lead to OOM and could be exploited.
* Availability impact realistic: +1 only for paranoid scoring. If repeated or large allocations can reliably pressure system memory, the impact can become system-wide OOM. This is not counted in the conservative score to avoid double-counting the DoS signal.
* No generic memory corruption: +0. The patch only adds upper-bound validation before memdup_user allocations. It does not show UAF, OOB write, double free, type confusion, refcount misuse, or arbitrary write.
* No confidentiality or integrity impact: +0. The visible primitive is resource exhaustion only.
* No high-control device API bonus: +0. This is a GPU ioctl, but the patch does not show attacker influence over object lifetime, callbacks, DMA mappings, page ownership, or allocator reuse beyond oversized allocation counts.

3. Reachability analysis
A local user or process with access to the AMDGPU DRM node can potentially trigger the path if amdgpu_userq is enabled. This is not network reachable. Containers or delegated GPU access may make the bug reachable by less trusted workloads, but the requirement remains local device access. The realistic exploit condition is memory pressure or OOM through oversized handle-count allocations, not memory corruption or privilege escalation.

4. Severity interpretation
This behaves like an ordinary Moderate or Low-like resource-exhaustion issue. Theoretical impact is local DoS via OOM. There is no evidence of a stronger primitive such as controlled overwrite, stale pointer reuse, page-cache corruption, or privilege escalation. Paranoid scoring reaches 3 because system-wide OOM is plausible, but this should not be treated as an Important-class kernel vulnerability.

5. One-sentence report phrase
amdgpu_userq_signal_ioctl lacked upper bounds on user supplied handle counts, allowing a local process with AMDGPU DRM access to request excessive kernel allocations and potentially cause OOM based denial of service.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. This is a validation-only resource exhaustion fix with no concrete memory corruption, confidentiality, integrity, or privilege escalation primitive shown by the patch.

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

Patch: drm/amdgpu: add upper bound check on user inputs in signal ioctl
Commit: 6fff5204d8aa26b1be50b6427f833bd3e8899c4f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6fff5204d8aa26b1be50b6427f833bd3e8899c4f

Commit description:

Huge input values in amdgpu_userq_signal_ioctl can lead to a OOM and
could be exploited.

So check these input value against AMDGPU_USERQ_MAX_HANDLES
which is big enough value for genuine use cases and could
potentially avoid OOM.

Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit be267e1 )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.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=6fff5204d8aa26b1be50b6427f833bd3e8899c4f

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

The original Linux kernel CVE announcement for CVE-2026-43400 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43400

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).