[CVE-2026-89995][MODERATE 7.0] dma-direct: return struct page from dma_direct_alloc_from_pool()

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

CVE: CVE-2026-89995
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: dma-direct: return struct page from dma_direct_alloc_from_pool()
Commit: c3fdb94da43ff23287f85664174c45c45e881a3f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c3fdb94da43ff23287f85664174c45c45e881a3f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89995
Analysis date: Wed, 16 Sep 2026 08:00:36 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A core dma-direct helper returned a CPU virtual address where `dma_direct_alloc_pages()` expected `struct page *`, creating a bogus page-pointer type confusion that can crash the kernel and may have unresolved memory-corruption impact in downstream DMA/page operations.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-89995 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89995

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-2026-89995	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89995 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-843;CWE-704;CWE-119;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'dma_direct_alloc_from_pool returned a CPU address from the coherent DMA pool even though dma_direct_alloc_pages expected a struct page * from the same helper. This can make callers treat a DMA buffer virtual address as a struct page pointer, which is an invalid pointer type confusion in a core DMA allocation path. For the CVSS the PR:L is used for the paranoid score because a local user or service may be able to trigger affected driver allocation paths through an accessible device or workload without full administrator privileges. The issue is not directly network reachable from the patch context. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact if later page operations corrupt memory through the bogus struct page pointer. Exposure depends on CONFIG_DMA_COHERENT_POOL, force_dma_unencrypted, atomic pool allocation conditions, and a driver using dma_direct_alloc_pages on the affected path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	OOB LOCK SIMPLEFIX HARDWARE KPANIC MEMORY 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

## 1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

No floor or cap was applied. The paranoid score is emitted as the final ActionableScore because the patch establishes a core DMA pointer type confusion where a CPU virtual address can be returned to a caller expecting `struct page *`.

## 2. Signal breakdown

Positive signals:

* +1 Weak / indirect corruption candidate: `dma_direct_alloc_from_pool()` returned a CPU address while `dma_direct_alloc_pages()` expected a `struct page *`.
* +1 Weak LPE concern: the bogus `struct page *` can plausibly be consumed by later page, DMA, refcount, mapping, or free logic, which is a meaningful structured-object misinterpretation beyond a plain NULL dereference.
* +1 Privileged kernel/device-management memory corruption path: the bug is in the core DMA allocation path and affects page/DMA ownership semantics, not only a local driver bookkeeping field.
* +1 Reliable kernel crash / strong DoS: treating a DMA buffer virtual address as `struct page *` can realistically lead to kernel fault or panic in downstream callers.
* +1 Paranoid unresolved corruption leverage: in the stronger defensible interpretation, later operations on the bogus `struct page *` may mutate state through an invalid page object rather than only faulting immediately.

Non-awarded or withheld signals:

* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Remote reachability not established.
* Real UAF not established.
* Concrete repeated release/refcount UAF not established.
* Confidentiality and integrity are not awarded as established consequences. They remain unresolved paranoid concerns because of the bogus `struct page *` propagation.
* Extra Availability was not awarded because the same likely crash is already counted.
* No race/timing penalty was applied because this is an ordered type/return-value bug, not a timing race.
* No host-admin penalty was applied because host-admin-equivalent triggering is not positively established.
* No rare-hardware penalty was applied because the supplied evidence shows specific DMA conditions, but not a positively rare physical-only requirement.

Repeated-release/refcount check:

* First release can end lifetime: not established.
* Exact same reference survives to a second release: not established.
* Second lifetime/refcount mutation: not established as a repeated-release pattern.
* Concrete repeated release/refcount +1: not awarded.
* Paranoid repeated-refcount leverage +1: not awarded.
* FLOOR 5 for repeated release: not applied.

## 3. Reachability analysis

The vulnerable path is reached through `dma_direct_alloc_pages()` when `force_dma_unencrypted(dev)` is true and `dma_direct_use_pool(dev, gfp)` selects the coherent DMA pool path. This also depends on `CONFIG_DMA_COHERENT_POOL` and on a driver or subsystem using `dma_direct_alloc_pages()` under those allocation conditions.

The direct trigger is local or device/workload mediated, not network reachable from the patch context. A local user or service might indirectly exercise the path through an accessible device or workload, but the supplied evidence does not prove a complete below-host-admin trigger chain. It also does not prove that host administrator privilege is required. Therefore `HostAdminRequired=UNKNOWN`.

No namespace-scoped privilege path is shown. There is no evidence that user namespaces or network namespaces make the complete DMA allocation path attacker-reachable below host admin, so `NamespaceScopedPrivilege=NO`.

The issue does not require a race. The main uncertainty is which real driver call sites can trigger the affected allocation path and what they do with the returned bogus `struct page *`.

## 4. Primitive and severity interpretation

The exact primitive is pointer type confusion / invalid structured-object interpretation: a CPU virtual address from the coherent DMA pool is returned where a `struct page *` is required. This is not a real UAF, but it can cause downstream code to treat ordinary DMA buffer memory as a kernel page descriptor.

This is an active structured-object problem, not fixed stale storage and not a pure warning. The demonstrated consequence is at least local kernel crash or serious invalid kernel state. The speculative but technically defensible consequence is broader memory corruption if later page/DMA operations mutate fields through the bogus `struct page *`.

Primitive class is `CLASS_B`: a real potentially exploitable kernel corruption/type-confusion primitive exists, but controlled reclaim, arbitrary read/write, callback control, or demonstrated LPE is not established.

`ImportantCandidate=YES` because the bug affects a core DMA allocation helper and leaves meaningful exploitation leverage unresolved. `AutoDowngradeAllowed=NO` because automatically closing this as an ordinary crash-only issue could miss a real page/DMA ownership corruption path.

Operationally this is at least Actionable Moderate and should receive manual review of affected `dma_direct_alloc_pages()` callers and platform conditions.

## 5. One-sentence report phrase

A core dma-direct helper returned a CPU virtual address where `dma_direct_alloc_pages()` expected `struct page *`, creating a bogus page-pointer type confusion that can crash the kernel and may have unresolved memory-corruption impact in downstream DMA/page operations.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

The patch establishes a concrete wrong-pointer-type primitive in a core DMA path, and downstream caller behavior is needed to determine whether the impact is limited to DoS or can affect memory/page ownership more broadly.

## 7. Call-site confidence

Call-site confidence: medium

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

Patch: dma-direct: return struct page from dma_direct_alloc_from_pool()
Commit: c3fdb94da43ff23287f85664174c45c45e881a3f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c3fdb94da43ff23287f85664174c45c45e881a3f

Commit description:

Commit 5b138c5 ("dma-direct: factor out a dma_direct_alloc_from_pool
helper") changed dma_direct_alloc_from_pool() to return the CPU address
from dma_alloc_from_pool(). That fits dma_direct_alloc(), but
dma_direct_alloc_pages() also uses the helper and expects a struct page *.

Fix this by making dma_direct_alloc_from_pool() return the struct page *
again, and pass the CPU address back through an out-parameter for the
dma_direct_alloc() caller.

Fixes: 5b138c5 ("dma-direct: factor out a dma_direct_alloc_from_pool helper")
Cc: stable@vger.kernel.org
Tested-by: Michael Kelley <mhklinux@outlook.com>
Tested-by: Mostafa Saleh <smostafa@google.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
Reviewed-by: Mostafa Saleh <smostafa@google.com>
Link: https://lore.kernel.org/r/20260717180442.110954-2-aneesh.kumar@kernel.org
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/dma/direct.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=c3fdb94da43ff23287f85664174c45c45e881a3f

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

The original Linux kernel CVE announcement for CVE-2026-89995 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89995

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: 5

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).