[CVE-2026-43370][MODERATE 7.0] drm/amdgpu: Fix use-after-free race in VM acquire

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

CVE: CVE-2026-43370
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: drm/amdgpu: Fix use-after-free race in VM acquire
Commit: ae87aea330c24f462fc7058ed543ba8bc6798447
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ae87aea330c24f462fc7058ed543ba8bc6798447
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43370
Analysis date: Thu, 30 Jul 2026 12:21:06 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local use-after-free race in the AMDGPU KFD VM acquire path can occur when forked processes sharing a drm_file concurrently acquire the same VM, allowing kernel crash and requiring manual review for possible privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-43370 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43370

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 7.0
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
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CVE-2026-43370	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use after free race in the amdgpu KFD VM acquire path can occur when parent and child processes share a drm_file after fork and both try to acquire the same VM. The old code assigned vm process_info non atomically, so two local callers could believe they own the same VM state and one error or cleanup path could free process_info while the other path still uses it. For the CVSS the PR:L is used because triggering requires local user access to the AMD GPU or KFD device interface, but not full administrator privileges in common render node deployments. The issue is not network reachable. Impact is at least local denial of service via kernel crash and a plausible privilege escalation risk 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 5) 	MAYBE	RACE UAF HARDWARE KPANIC MEMORY 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local user with access to AMDGPU KFD or DRM render node can plausibly reach VM acquisition paths.
* Memory corruption, weak primitive: +1. The commit explicitly describes a use-after-free race, but the patch does not show controlled reclaim, type confusion, callback hijack, or arbitrary write.
* Real lifetime corruption: +1. The bug is a race in ownership of `vm->process_info`, with cleanup potentially freeing state still considered active by another racing caller.
* Reliable kernel crash / strong DoS: +1. UAF in GPU VM management can realistically crash the kernel.
* Hard race / timing required: -1. Trigger depends on parent and child sharing a `drm_file` after fork and racing VM acquisition.
* Privileged device-management / VM lifetime path: +1. The corruption is in AMDGPU KFD GPUVM state, a trusted kernel memory-management path.

Paranoid additional signal:

* Weak LPE concern: +1. Although no concrete reclaim or overwrite primitive is shown, this is kernel UAF in a complex GPU VM subsystem reachable from local device interfaces, so privilege escalation cannot be ruled out without manual analysis.

## 3. Reachability analysis

The bug is local, not network reachable. Triggering requires a process that can access the AMDGPU KFD or DRM interface, typically through `/dev/kfd` or DRM render nodes. On many desktop, workstation, and GPU-compute systems, render-node style access can be granted to non-root users via local group membership, so PR:L is more realistic than PR:H. Containers may matter if GPU devices are passed through or exposed to workloads. The affected path is not universal across all Linux systems, but it is relevant on AMD GPU systems with KFD/ROCm or similar GPU compute usage.

Call-site confidence: medium. The provided patch shows the vulnerable assignment and cleanup path, but not the full ioctl call chain.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because the patch fixes an explicit UAF race in kernel GPU VM state. Realistic demonstrated impact is at least local DoS via kernel crash. Practical privilege escalation is not demonstrated by the patch, because there is no shown attacker-controlled reclaim, overwrite, type confusion, or callback dispatch. However, due to the subsystem complexity and explicit lifetime corruption, it should be treated as Actionable Moderate at minimum and a Strong Important candidate for manual review.

## 5. One-sentence report phrase

A local use-after-free race in the AMDGPU KFD VM acquire path can occur when forked processes sharing a drm_file concurrently acquire the same VM, allowing kernel crash and requiring manual review for possible privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

Reason: explicit kernel UAF race, local unprivileged or low-privileged reachability on common GPU deployments, and plausible but unproven LPE risk in a complex GPU VM lifetime path.

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UPSTREAM PATCH SUMMARY
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Patch: drm/amdgpu: Fix use-after-free race in VM acquire
Commit: ae87aea330c24f462fc7058ed543ba8bc6798447
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ae87aea330c24f462fc7058ed543ba8bc6798447

Commit description:

Replace non-atomic vm->process_info assignment with cmpxchg()
to prevent race when parent/child processes sharing a drm_file
both try to acquire the same VM after fork().

Reviewed-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Signed-off-by: Alysa Liu <Alysa.Liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit c7c5732 )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.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=ae87aea330c24f462fc7058ed543ba8bc6798447

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

The original Linux kernel CVE announcement for CVE-2026-43370 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43370

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:H/PR:L/UI:N/S:U/C:L/I:L/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: 4
  Paranoid ActionableScore: 6

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).