[CVE-2026-46215][IMPORTANT] drm: Set old handle to NULL before prime swap in change_handle

[CVE-2026-46215][IMPORTANT] drm: Set old handle to NULL before prime swap in change_handle

[AL-KERNEL]

CVE: CVE-2026-46215
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: drm: Set old handle to NULL before prime swap in change_handle
Commit: 672464dd53231509c9c771110798c56d4660e19e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=672464dd53231509c9c771110798c56d4660e19e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46215
Analysis date: Wed, 01 Jul 2026 20:15:06 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in `drm_gem_change_handle_ioctl()` can leave a dangling GEM IDR handle after concurrent `gem_close`, allowing later dereference of freed `drm_gem_object` memory and creating a local UAF with DoS and possible LPE concern.

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

The original Linux kernel CVE announcement for CVE-2026-46215 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46215

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
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CVE-2026-46215	IMPORTANT	CHECK	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-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'drm_gem_change_handle_ioctl could temporarily expose one GEM object through two IDR handles during handle reassignment. A concurrent gem_close could drop the object and remove one handle while leaving the other handle dangling, allowing a later dereference of freed GEM object memory. For the CVSS the PR:L is used because a local user with access to a DRM device or render node can exercise GEM handle ioctls without full administrative privileges. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact because this is a kernel use-after-free race in DRM object lifetime handling.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) 	MAYBE	LOCK RACE ERRORPATH UAF HARDWARE KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 8
* 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 a DRM device or render node can exercise GEM handle ioctls.
* Generic memory corruption: +2. The patch describes a real use-after-free caused by a dangling GEM handle.
* Real lifetime corruption: +1. One IDR handle can remain pointing to a freed `drm_gem_object`.
* Reliable kernel crash / strong DoS: +1. Dereferencing the dangling handle can crash the kernel.
* Broad/common subsystem: +1. DRM GEM and render-node access are common on desktop, workstation, and GPU-enabled container systems.
* Hard or timing-dependent race: -1. Exploitation requires racing `change_handle` against `gem_close`.

Paranoid additional signals:

* Weak to strong LPE concern: +1. This is a UAF in a user-accessible kernel object lifetime path, but no controlled reclaim or write primitive is shown in the patch.
* Confidentiality / integrity impact plausible: +1 combined. UAF in DRM GEM object handling can potentially move beyond DoS if freed object reuse is controllable, but this remains a manual-review hypothesis rather than demonstrated exploitation.

## 3. Reachability analysis

The bug is local and reachable through DRM GEM handle management. A user with access to a render node or DRM device can potentially call the relevant ioctl and race it with `gem_close`.

Containers matter if GPU devices or render nodes are passed through. In that case, a containerized workload may have enough access to trigger the bug without host root. The issue is not remotely network reachable.

The path is not exotic. DRM render nodes are commonly available to unprivileged graphics or compute users, although exact access depends on device permissions and container policy.

## 4. Severity interpretation

This behaves like a Strong Important candidate under paranoid triage and at least an actionable Moderate. The realistic demonstrated impact is local DoS through kernel crash. The theoretical higher impact is possible privilege escalation because the primitive is a real UAF race in a user-reachable DRM object lifetime path.

No arbitrary write or concrete exploit chain is shown, so the score should not be treated as proven LPE, but it should not be auto-closed.

## 5. One-sentence report phrase

A race in `drm_gem_change_handle_ioctl()` can leave a dangling GEM IDR handle after concurrent `gem_close`, allowing later dereference of freed `drm_gem_object` memory and creating a local UAF with DoS and possible LPE concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is a real kernel use-after-free race in a commonly exposed DRM GEM path, potentially reachable by unprivileged users with render-node access.

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

Patch: drm: Set old handle to NULL before prime swap in change_handle
Commit: 672464dd53231509c9c771110798c56d4660e19e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=672464dd53231509c9c771110798c56d4660e19e

Commit description:

There was a potential race condition in change_handle. The ioctl
briefly had a single object with two idr entries; a concurrent
gem_close could delete the object and remove one of the handles
while leaving the other one dangling, which could subsequently
be dereferenced for a use-after-free.

To fix this, do the same dance that gem_close itself does.
( f6cd7da drm: Release driver references to handle before making it available again)
First idr_replace the old handle to NULL. Later, if the prime
operations are successful, actually close it.

create_tail required a similar dance to avoid a similar problem.
( bd46cec drm/gem: Fix race in drm_gem_handle_create_tail())
It idr_allocs the new handle with NULL, then swaps in the correct
object later to avoid races. We don't need to do that here, since
the only operations that could race are drm_prime, and
change_handle holds the prime lock for the entire duration.

v2: cleanups of error paths

Signed-off-by: David Francis <David.Francis@amd.com>
Co-authored-by: Dave Airlie <airlied@gmail.com>
Reported-by: Puttimet Thammasaeng <pwn8official@gmail.com>
Tested-by: Vitaly Prosyak <Vitaly.Prosyak@amd.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: stable@vger.kernel.org
Cc: Christian Koenig <Christian.Koenig@amd.com>
Fixes: 5309672 ("drm: Add DRM prime interface to reassign GEM handle")
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/drm_gem.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=672464dd53231509c9c771110798c56d4660e19e

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

The original Linux kernel CVE announcement for CVE-2026-46215 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46215

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: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: 8

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).