[CVE-2026-93284][MODERATE REGULAR] drm/pagemap: dma-unmap pages before handling migration errors [ Upstream

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

CVE: CVE-2026-93284
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/pagemap: dma-unmap pages before handling migration errors [ Upstream
Commit: e4331c6644db85bc6ceb470bd84bcf371b6dbfa6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e4331c6644db85bc6ceb470bd84bcf371b6dbfa6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93284
Analysis date: Thu, 24 Sep 2026 20:31:12 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-93284 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93284

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: 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-2026-93284	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-93284 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:L/I:L/A:H';CWE-404;*CWE-664;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.8';DESCR 'A DRM pagemap migration error path can clear the destination page array before DMA mappings are removed. This can leave stale DMA mappings after a failed migration and may exhaust DMA or IOMMU resources through repeated failures. For the CVSS the PR:L value is selected because a local user with access to a DRM render device can potentially exercise GPU memory allocation and migration paths. Reliable triggering requires a migration failure after DMA mappings were prepared so AC:H is appropriate. The issue is not directly network reachable. The base impact is limited availability loss. In a worst case stale DMA access to pages after their lifetime changes may cause limited confidentiality or integrity impact and a system wide denial of service. This potential DMA lifetime issue should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	SIMPLEFIX DMAorINTERRUPT HARDWARE MEMORY  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended**::

No floor or cap was applied.

2. Signal breakdown

Conservative:

* +1 Concrete persistent kernel resource leak. The error path clears the destination page array before `drm_pagemap_migrate_unmap_pages()` can identify and unmap the DMA mappings. The normal cleanup path therefore loses the information needed to release those mappings.
* +1 Active-state retirement failure. DMA mappings are active device translation resources and the required DMA-unmap retirement step is bypassed on the migration error path after the page references are cleared.

Paranoid only:

* +1 Weak indirect corruption concern. A stale DMA mapping can outlive the page-array ownership information. If an affected device mapping remains usable while the physical page lifetime changes, this could become a stale DMA access concern. The patch alone does not establish continued device DMA, attacker-controlled device commands, or page reuse.

Not awarded:

* No Real UAF signal. The patch does not establish dereference or refcount mutation through a freed kernel object. It establishes loss of page metadata needed to release DMA mappings.
* No controlled reclaim, object replacement, arbitrary write, callback control, or refcount takeover is demonstrated.
* No confidentiality or integrity point is awarded. The possibility of stale DMA access is not equivalent to demonstrated disclosure or unauthorized modification.
* No reliable kernel crash or host-wide DoS point is awarded. Resource leakage and possible DMA/IOMMU exhaustion are plausible, but a crash or host-wide exhaustion is not shown.
* No local-unprivileged trigger point is awarded. Access to a DRM render node may be available to non-admin users on some systems, but the supplied patch does not establish that such a user can complete the full GPU SVM migration and error sequence.
* No host-admin penalty is applied. Host-admin-equivalent privilege is not positively established.
* No race penalty is applied. This is an ordered error-cleanup sequencing defect, not a demonstrated narrow timing race.
* No niche or hardware penalty is applied. GPU hardware is involved, but the patch does not establish a rare-hardware or physical-only requirement.

3. Reachability analysis

The vulnerable path is local and concerns DRM pagemap GPU-memory migration error handling. It is not directly network reachable.

The relevant attacker model is unresolved. A normal logged-in user may have access to a DRM render node, while DRM master, compositor, display server, delegated graphics service, and host administrator may have broader capabilities. The supplied diff does not show which actor can reliably allocate the required pagemap-backed memory, initiate migration, and induce the error path after DMA mappings were created.

No capability check or complete namespace-scoped trigger chain is visible. Therefore, `HostAdminRequired=UNKNOWN` and `NamespaceScopedPrivilege=UNKNOWN` are appropriate. No prior privileged setup, GPU-driver-specific prerequisite, IOMMU configuration, or device-command behavior is established by the supplied material.

4. Primitive and severity interpretation

The exact defect is a DMA mapping lifecycle and cleanup-ordering error. On a migration failure, `drm_pagemap_migration_unlock_put_pages()` clears the destination page array before `drm_pagemap_migrate_unmap_pages()` runs. The later unmap helper can no longer identify the pages whose DMA mappings must be removed.

This is not an ordinary CPU-side use-after-free. It is also not a demonstrated DMA write-after-free. The patch establishes that DMA mappings can be left uncleared, but it does not establish that the device can continue DMA after the migration failure, that an attacker controls subsequent DMA, or that reused pages can be targeted.

The primitive is therefore `CLASS_C`: an invalid resource-lifetime state with potential resource leakage and stale translation state. The demonstrated practical consequence is incomplete DMA mapping cleanup. The stronger speculative consequence is stale device DMA access after page lifetime changes, but that requires driver and device behavior not present in the supplied evidence.

`ImportantCandidate=NO` because no active CPU UAF, controlled DMA primitive, cross-process memory corruption, or security-boundary bypass is established. `AutoDowngradeAllowed=YES` because the demonstrated bug is a constrained error-path DMA cleanup failure rather than a proven exploitable corruption primitive. Manual review remains recommended because DMA and IOMMU lifetime behavior can be driver-specific and may materially change the impact.

Likely operational severity is Low to ordinary Moderate. The paranoid score preserves a review signal for environments where the affected DRM driver can retain active DMA access after migration cleanup failure.

5. One-sentence report phrase

A DRM pagemap migration error path can lose page information before DMA mappings are removed, causing incomplete DMA cleanup and a possible stale DMA mapping or resource-leak condition.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review the affected DRM driver DMA mapping ownership, whether a migration failure can leave device DMA active, whether an IOMMU mapping remains usable after page release, and whether an unprivileged render-node user can reliably induce the complete migration error path.

7. Call-site confidence

Call-site confidence: medium

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

Patch: drm/pagemap: dma-unmap pages before handling migration errors [ Upstream
Commit: e4331c6644db85bc6ceb470bd84bcf371b6dbfa6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e4331c6644db85bc6ceb470bd84bcf371b6dbfa6

Changed files:
  drivers/gpu/drm/drm_pagemap.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=e4331c6644db85bc6ceb470bd84bcf371b6dbfa6

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

The original Linux kernel CVE announcement for CVE-2026-93284 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93284

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:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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).