[CVE-2026-31566][IMPORTANT] drm/amdgpu: Fix fence put before wait in amdgpu_amdkfd_submit_ib [ Upstream

[CVE-2026-31566][IMPORTANT] drm/amdgpu: Fix fence put before wait in amdgpu_amdkfd_submit_ib [ Upstream

[AL-KERNEL]

CVE: CVE-2026-31566
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: drm/amdgpu: Fix fence put before wait in amdgpu_amdkfd_submit_ib [ Upstream
Commit: bc7760c107dc08ef3e231d72c492e67b0a86848b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bc7760c107dc08ef3e231d72c492e67b0a86848b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-31566
Analysis date: Thu, 30 Jul 2026 12:34:36 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local use-after-free in `amdgpu_amdkfd_submit_ib()` can occur when a DMA fence reference is released before waiting on it, allowing a user with access to the AMD GPU KFD or DRM render path to trigger a kernel crash and requiring manual review for possible privilege escalation impact.

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

The original Linux kernel CVE announcement for CVE-2026-31566 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-31566

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: IMPORTANT
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-2026-31566	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-672;CWE-825;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use-after-free can occur in amdgpu_amdkfd_submit_ib() because dma_fence_put() may release the last reference to the fence before dma_fence_wait() is called on the same object. A local user or process with access to the AMD GPU KFD or DRM render device path may be able to trigger the bug while submitting GPU work, causing a kernel crash or other undefined behavior. For the CVSS the PR:L is used because triggering requires local code execution and access to the relevant GPU device interface, but not full administrator privileges in typical GPU compute deployments. The issue is not network reachable and is local to systems exposing the affected AMD GPU driver path. Impact is at least a local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel use-after-free memory corruption, so manual review is recommended.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-31566  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	INIT UAF HARDWARE KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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

ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local user or process with access to AMD KFD or DRM render device nodes may reach GPU job submission paths without full administrator privileges in common GPU compute setups.

* Memory corruption, strong corruption primitive: +2
  The patch and commit explicitly describe a use-after-free where `dma_fence_put()` may release the last reference before `dma_fence_wait()` uses the same fence.

* Real lifetime corruption: +1
  This is a reference lifetime ordering bug involving `dma_fence_put()` and later use of the same object.

* Reliable kernel crash / strong DoS: +1
  The described outcome includes passing freed memory to `dma_fence_wait()`, which can plausibly lead to kernel crash or undefined behavior.

* Broad/common deployed exposure: +1
  AMD GPU and KFD paths are hardware-dependent but common in workstation, compute, and accelerator deployments where device nodes may be exposed to users.

* Weak LPE concern, paranoid only: +1
  Kernel UAF in a local device path can sometimes become exploitable beyond DoS, but this patch does not show attacker-controlled reclaim, overwrite, callback control, or type confusion. Therefore this is weak LPE concern only, not strong LPE plausibility.

## 3. Reachability analysis

The bug is local, not network reachable. Triggering likely requires access to AMD GPU KFD or DRM render interfaces and the ability to submit GPU work through the affected path. This is typically PR:L rather than PR:H because render nodes and GPU compute interfaces are often intentionally available to non-root users. Containers may matter if GPU device nodes are passed through to container workloads. The path is not universally default-enabled because it depends on AMD GPU hardware and driver exposure, but it is realistic in GPU compute and desktop deployments.

Call-site confidence: high. The patch shows the exact lifetime misuse and the immediate use-after-put sequence.

## 4. Severity interpretation

This behaves above an ordinary Moderate because it is an explicit kernel use-after-free in a locally reachable GPU driver path. The conservative interpretation is Actionable Moderate because the demonstrated impact is mainly crash or undefined behavior, without a proven reclaim or write primitive. The paranoid interpretation reaches Strong Important candidate because local kernel UAF bugs in device submission paths historically deserve manual review for privilege escalation potential, even when the patch itself only proves the lifetime violation and likely DoS.

## 5. One-sentence report phrase

A local use-after-free in `amdgpu_amdkfd_submit_ib()` can occur when a DMA fence reference is released before waiting on it, allowing a user with access to the AMD GPU KFD or DRM render path to trigger a kernel crash and requiring manual review for possible privilege escalation impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is an explicit kernel UAF candidate in a local device path with realistic non-root reachability on systems exposing AMD GPU compute or render nodes.

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

Patch: drm/amdgpu: Fix fence put before wait in amdgpu_amdkfd_submit_ib [ Upstream
Commit: bc7760c107dc08ef3e231d72c492e67b0a86848b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bc7760c107dc08ef3e231d72c492e67b0a86848b

Changed files:
  drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.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=bc7760c107dc08ef3e231d72c492e67b0a86848b

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

The original Linux kernel CVE announcement for CVE-2026-31566 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-31566

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:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 6
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).