[CVE-2026-43398][MODERATE REGULAR] drm/amdgpu: add upper bound check on user inputs in wait ioctl

[CVE-2026-43398][MODERATE REGULAR] drm/amdgpu: add upper bound check on user inputs in wait ioctl

[AL-KERNEL]

CVE: CVE-2026-43398
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amdgpu: add upper bound check on user inputs in wait ioctl
Commit: b1d10508da559da2e0ca9cca6505094a7df948e1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b1d10508da559da2e0ca9cca6505094a7df948e1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43398
Analysis date: Sat, 01 Aug 2026 12:21:43 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate / Borderline local DoS, not Important
Manual review required: NO

Summary:
`amdgpu_userq_wait_ioctl accepted unbounded user supplied handle counts, allowing a local DRM device user to request excessive kernel allocations and potentially trigger OOM based denial of service.`

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

The original Linux kernel CVE announcement for CVE-2026-43398 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43398

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-2026-43398	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-770;**CWE-400;CWE-789;BEST CVSS score: '5.5';DESCR 'amdgpu_userq_wait_ioctl accepted user controlled handle counters without an upper bound. Very large num_syncobj_handles, num_bo_write_handles, or num_bo_read_handles values can drive large kernel allocations in the wait ioctl path and may trigger OOM on the host. For the CVSS the PR:L value is used because reliable triggering requires a local process with access to the AMDGPU DRM device, but it does not normally require full root privileges. The issue is not network reachable and is exposed through a local device ioctl. Impact is denial of service through memory exhaustion. No concrete UAF, OOB write, arbitrary write, or information leak primitive is indicated by the patch context, so confidentiality and integrity remain unaffected.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Borderline local DoS, not Important (with actual score 3) 	MAYBE	SIMPLEFIX HARDWARE  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE 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: **Ordinary Moderate / Borderline local DoS, not Important**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local process with access to the AMDGPU DRM device can call the wait ioctl. This usually does not require full root privileges on systems exposing render or video device nodes to users.

* Availability impact realistic: +1
  Huge user supplied handle counts can drive large kernel allocations through memdup_user and related wait ioctl handling, potentially causing OOM.

Paranoid-only signal:

* Reliable kernel crash / strong DoS: +1
  Counted only in the paranoid score because the commit explicitly says huge values can lead to OOM. This is still resource exhaustion, not memory corruption.

Not counted:

* No generic memory corruption. The patch only adds upper bound validation before allocation.
* No UAF, double free, OOB write, arbitrary write, type confusion, or information leak is shown.
* No privilege escalation plausibility beyond generic OOM impact.
* No high-control API bonus. DRM ioctls expose kernel objects, but this patch does not show attacker control over object lifetime, callbacks, refcounts, DMA ownership, or memory layout relevant to exploitation.
* No remote reachability.

## 3. Reachability analysis

The bug is reachable locally through `amdgpu_userq_wait_ioctl()` when AMDGPU user queues are enabled and the caller has access to the DRM device. In typical desktop or GPU compute deployments, such access may be available to non-root users through `render` or `video` group permissions. Containers can matter if GPU device nodes are passed through, but this is still a local device-interface attack rather than a network attack.

The path is hardware and configuration dependent because it requires AMDGPU and userq support. Exploitation conditions are realistic for local DoS if an untrusted user can access the relevant device node, but the demonstrated primitive is only excessive allocation leading to OOM.

## 4. Severity interpretation

This behaves like an ordinary Moderate local resource exhaustion issue, not an Important-class kernel vulnerability. The realistic impact is local denial of service via memory exhaustion. Theoretical exploitation beyond DoS is not supported by the patch because there is no concrete memory corruption, stale pointer, object confusion, controlled overwrite, or disclosure primitive.

## 5. One-sentence report phrase

`amdgpu_userq_wait_ioctl accepted unbounded user supplied handle counts, allowing a local DRM device user to request excessive kernel allocations and potentially trigger OOM based denial of service.`

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: this is a local resource exhaustion validation fix with no evidence of memory corruption, privilege escalation, information disclosure, or network reachability.

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

Patch: drm/amdgpu: add upper bound check on user inputs in wait ioctl
Commit: b1d10508da559da2e0ca9cca6505094a7df948e1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b1d10508da559da2e0ca9cca6505094a7df948e1

Commit description:

Huge input values in amdgpu_userq_wait_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.

v2: squash in Srini's fix

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 fcec012 )
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=b1d10508da559da2e0ca9cca6505094a7df948e1

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

The original Linux kernel CVE announcement for CVE-2026-43398 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43398

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: Not available
  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).