[CVE-2026-43399][MODERATE REGULAR] drm/amdgpu/userq: Fix reference leak in amdgpu_userq_wait_ioctl

[CVE-2026-43399][MODERATE REGULAR] drm/amdgpu/userq: Fix reference leak in amdgpu_userq_wait_ioctl

[AL-KERNEL]

CVE: CVE-2026-43399
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amdgpu/userq: Fix reference leak in amdgpu_userq_wait_ioctl
Commit: 762f47e2b824383d5be65eee2c40a1269b7d50c8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=762f47e2b824383d5be65eee2c40a1269b7d50c8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43399
Analysis date: Sat, 01 Aug 2026 12:17:25 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: YES

Summary:
A local reference leak in `amdgpu_userq_wait_ioctl()` can occur when an undersized output array aborts the IOCTL without dropping a `dma_fence` reference, allowing repeated calls to cause gradual kernel resource exhaustion.

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

The original Linux kernel CVE announcement for CVE-2026-43399 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43399

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.

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

CVE-2026-43399	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-772;*CWE-401;**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 'A reference leak in amdgpu_userq_wait_ioctl can occur when the ioctl aborts because the user supplied output array is too small for the number of fences. The failing path returns EINVAL but previously did not drop the current dma_fence reference, so repeated calls can keep syncobj or timeline fence objects alive longer than intended. For the CVSS the PR:L is used because a local user or process with access to the AMDGPU DRM device node can trigger the ioctl path, but no administrative privilege is normally required on systems that expose render nodes to users. The issue is not network reachable and requires local access to the GPU device interface. Impact is denial of service through gradual kernel resource exhaustion, not information disclosure or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 3) 	MAYBE	SIMPLEFIX LEAK HARDWARE MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

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

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local process with access to the AMDGPU DRM device node or render node can plausibly call `amdgpu_userq_wait_ioctl()`. No host root privilege is normally required on systems exposing GPU render nodes to users.

* Availability impact realistic: +1
  Repeated failing IOCTL calls with an undersized output array can leak references to syncobj or timeline fence objects, causing gradual kernel resource exhaustion.

Paranoid-only signal:

* Real lifetime corruption: +1
  This is a reference lifetime bug involving missing `dma_fence_put()`. However, it is a reference leak, not a demonstrated UAF, double free, stale callback, or object replacement primitive.

Not triggered:

* Remote reachable: +0
  This is a local DRM IOCTL path, not network reachable.

* Generic memory corruption: +0
  The patch only adds missing `dma_fence_put()` calls on error paths. It does not show UAF, OOB write, type confusion, arbitrary write, or attacker-controlled reclaim.

* Privilege escalation plausible: +0
  No evidence of reclaim control, callback hijack, write-after-free, or sensitive object corruption.

* Reliable kernel crash / strong DoS: +0 conservative
  The likely impact is gradual resource exhaustion, not an immediate reliable kernel crash from one or a few calls.

## 3. Reachability analysis

The bug is reachable by a local user or process that can open the affected AMDGPU DRM interface and issue the userqueue wait IOCTL. In typical desktop or GPU compute deployments, render nodes may be accessible to non-root users, so PR:L is the practical assumption. Containers or sandboxed services with GPU device access could also trigger it if the relevant device node is passed through.

The path is hardware and driver dependent because it requires AMDGPU userqueue support, introduced in the affected kernel range. It is not remotely reachable and does not appear to cross a namespace or credential boundary by itself.

Call-site confidence: high. The patch directly shows the error paths in `amdgpu_userq_wait_ioctl()` where the current fence reference was not dropped before jumping to cleanup.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource leak, not an Important-class vulnerability. The theoretical worst case is local denial of service through sustained kernel resource exhaustion. The patch context does not support confidentiality impact, integrity impact, privilege escalation, UAF exploitation, or arbitrary memory corruption.

The paranoid score is slightly higher because fence references are kernel lifetime-managed objects, but the primitive remains a leak rather than attacker-controlled memory corruption.

## 5. One-sentence report phrase

A local reference leak in `amdgpu_userq_wait_ioctl()` can occur when an undersized output array aborts the IOCTL without dropping a `dma_fence` reference, allowing repeated calls to cause gradual kernel resource exhaustion.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED.
NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED.

This is a local resource leak without evidence of memory corruption, privilege escalation, information disclosure, or network reachability.

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

Patch: drm/amdgpu/userq: Fix reference leak in amdgpu_userq_wait_ioctl
Commit: 762f47e2b824383d5be65eee2c40a1269b7d50c8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=762f47e2b824383d5be65eee2c40a1269b7d50c8

Commit description:

Drop reference to syncobj and timeline fence when aborting the ioctl due
output array being too small.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Fixes: a292fde ("drm/amdgpu: Implement userqueue signal/wait IOCTL")
Cc: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 68951e9 )
Cc: <stable@vger.kernel.org> # v6.16+
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=762f47e2b824383d5be65eee2c40a1269b7d50c8

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

The original Linux kernel CVE announcement for CVE-2026-43399 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43399

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).