[CVE-2026-52950][IMPORTANT] drm/xe/dma-buf: fix UAF with retry loop

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

CVE: CVE-2026-52950
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: drm/xe/dma-buf: fix UAF with retry loop
Commit: 39fdac6be02eb7c3460518c1c4085f75f935c4ce
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=39fdac6be02eb7c3460518c1c4085f75f935c4ce
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52950
Analysis date: Fri, 26 Jun 2026 13:45:49 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local use-after-free in drm/xe dma-buf import can occur when the retry path reuses a freed `xe_bo` after an init error, allowing a local DRM user to crash the kernel and potentially requiring manual review for privilege escalation risk.

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

The original Linux kernel CVE announcement for CVE-2026-52950 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52950

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-2026-52950	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-672;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'drm/xe dma-buf import can hit a use-after-free because the retry path may reuse a xe_bo storage object that was already freed after an init error. The bug is in the dma-buf import control path where xe_dma_buf_init_obj took ownership of the preallocated bo, while drm_exec retry handling could attempt the operation again after xe_bo_init_locked had freed that storage. For the CVSS the PR:L is used because a local user with access to a DRM render node or dma-buf import path may be able to trigger the vulnerable import flow. The issue is not network reachable and requires local interaction with the GPU driver. Impact is at least local denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to kernel use-after-free, so manual review is required.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-52950  SKIP The Fixes patch not applied yet, so unlikely that actual: eb289a5f6cc668853f9b2ea6aca04afe58ed11c7 YES  NO NO unknown 	MAYBE	INIT ERRORPATH UAF DMAorINTERRUPT HARDWARE TEST KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  The affected path is dma-buf import in the drm/xe driver. A local user with access to a DRM render node or relevant dma-buf import path may be able to reach it.
* Memory corruption, Strong corruption primitive: +2
  The commit explicitly says retry can lead to UAF because `bo` is freed on error and then reused.
* Real lifetime corruption: +1
  This is a real ownership and lifetime bug involving `xe_bo` storage freed by `xe_bo_init_locked()` error paths.
* Reliable kernel crash / strong DoS: +1
  UAF in a GPU kernel object path can realistically produce a kernel crash.
* Weak LPE concern: +1
  UAF in a local kernel driver path can sometimes be shaped into privilege escalation, but this patch does not show a demonstrated reclaim or controlled overwrite primitive.
* Hard or unreliable retry/timing condition: -1
  Triggering depends on the retry/error path around `drm_exec_retry_on_contention()` and init failure, so exploitation is less straightforward than a direct UAF.

Conservative total: 5

Paranoid additional interpretation:

* Privilege escalation plausible: +2 instead of weak LPE +1
  Because this is an explicit kernel UAF in a local GPU object path, the highest still defensible interpretation treats it as a manual-review LPE candidate even though exploitation is not demonstrated.
* Privileged kernel/device-management memory corruption path: +1
  The corruption occurs in a trusted DRM/GPU memory-management path involving dma-buf attachment and `xe_bo` lifetime.

Paranoid total: 7

## 3. Reachability analysis

The bug is local, not network reachable. The likely trigger requires a process that can interact with the Intel Xe DRM driver and import a dma-buf through the PRIME/dma-buf path. On many desktop or GPU-enabled systems, DRM render nodes are intentionally available to non-root users in the appropriate local access group, so PR:L is the practical CVSS privilege assumption rather than PR:H.

Namespaces and containers may matter if GPU device nodes are passed through to containers. A container user with access to `/dev/dri/renderD*` could potentially reach the same kernel driver path, so the issue should not be dismissed as host-root-only. Exposure depends on Intel Xe hardware, the `drm/xe` driver being enabled, and kernel versions affected by the referenced conversion.

## 4. Severity interpretation

This behaves above ordinary Moderate because the patch explicitly fixes a use-after-free, not only a warning or resource leak. Realistic demonstrated impact is local DoS through kernel memory lifetime corruption. Theoretical privilege escalation is plausible because UAF in a local GPU memory-management path can sometimes become exploitable, but the patch does not provide evidence of reliable object reclaim, attacker-controlled overwrite, or a complete LPE primitive.

Conservative handling is Actionable Moderate. Paranoid handling is Strong Important candidate due to explicit UAF in a local kernel driver path reachable by non-root GPU users.

## 5. One-sentence report phrase

A local use-after-free in drm/xe dma-buf import can occur when the retry path reuses a freed `xe_bo` after an init error, allowing a local DRM user to crash the kernel and potentially requiring manual review for privilege escalation risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch explicitly fixes a UAF in a local kernel GPU memory-management path, and local DRM render-node exposure makes the bug practically relevant even without a demonstrated exploit chain.

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

Patch: drm/xe/dma-buf: fix UAF with retry loop
Commit: 39fdac6be02eb7c3460518c1c4085f75f935c4ce
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=39fdac6be02eb7c3460518c1c4085f75f935c4ce

Commit description:

Retry doesn't work here, since bo will be freed on error, leading to
UAF. However, now that we do the alloc & init before the attach, we can
now combine this as one unit and have the init do the alloc for us. This
should make the retry safe.

Reported by Sashiko.

v2: Fix up the error unwind (CI)

Closes: https://sashiko.dev/#/patchset/20260506184332.86743-2-matthew.auld%40intel.com
Fixes: eb289a5 ("drm/xe: Convert xe_dma_buf.c for exhaustive eviction")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: <stable@vger.kernel.org> # v6.18+
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patch.msgid.link/20260508102635.149172-4-matthew.auld@intel.com
(cherry picked from commit 4796694 )
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/xe/xe_dma_buf.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=39fdac6be02eb7c3460518c1c4085f75f935c4ce

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

The original Linux kernel CVE announcement for CVE-2026-52950 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52950

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: 5
  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).