[CVE-2026-89573][MODERATE 7.0] dm array: reject an array block whose value size is not the caller's

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

CVE: CVE-2026-89573
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: dm array: reject an array block whose value size is not the caller's
Commit: 7bf4b5cb42a4e27f36bcbc6209d82a5da9c0168c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7bf4b5cb42a4e27f36bcbc6209d82a5da9c0168c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89573
Analysis date: Fri, 11 Sep 2026 22:33:08 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
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-2026-89573 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89573

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-89573	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89573 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-125;*CWE-20;CWE-754;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '6.6';DESCR 'A crafted dm array metadata block can pass the internal array_block_check while using a value_size that does not match the caller expected value size. In dm-cache this can make the mappings array root point at a hint block, so code that expects 8-byte mapping entries walks 4-byte hint entries with the wrong stride and can read beyond a 4096-byte metadata block. This is an out of bounds read in the kernel metadata loading path and can cause at least a local denial of service during dm-cache activation. For the CVSS the PR:L is used for the higher score because a local user or service with delegated storage management, loop device access, or access to crafted block metadata may be able to trigger activation in some deployments without full host root. The issue is not network reachable and requires crafted local storage metadata. Impact is at least kernel crash or device activation failure, with limited confidentiality or integrity impact possible from the OOB read and metadata interpretation path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 4)	YES	DISK SIMPLEFIX LINUS  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
ActionableScoreLower=3
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 4
* Paranoid score: 5. Applied manual review safety floor 4 -> 5 because crafted storage metadata causes an OOB read through semantic reinterpretation of active dm-cache array metadata.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Positive conservative signals:

* +1 Limited OOB read / weak corruption concern. A crafted array block with value_size 4 can be walked by a caller expecting value size 8, causing element_at() to read past a 4096-byte metadata block.
* +1 Important filesystem/storage metadata path. The bug is in dm persistent data / dm-cache metadata loading, where metadata interpretation affects cache mapping state.
* +1 Reliable DoS concern. The OOB read can plausibly cause kernel fault, metadata-load failure, or device activation failure.

Positive paranoid signals:

* +2 Stronger semantic reinterpretation concern. Crafted metadata that is internally valid as one dm array type can be consumed under a different caller value-size semantic, mapping hints as mappings and causing incorrect stride calculation.
* +1 Important filesystem/storage metadata path.
* +1 Reliable DoS concern.
* Floor to 5 because the established primitive is not a mere warning or passive bookkeeping issue. It is crafted on-disk metadata causing kernel OOB access in an active storage metadata path.

Non-awarded signals:

* No RealUAF. The patch does not establish stale lifetime use, double release, or refcount corruption.
* No concrete repeated release/refcount signal.
* No arbitrary write demonstrated.
* No controlled reclaim demonstrated.
* No confidentiality bonus awarded because no user-visible disclosure path is shown.
* No integrity bonus awarded because no concrete unauthorized write or persistent cross-object data corruption is established.
* No remote reachability awarded. The issue requires crafted local storage metadata.
* No extra availability point awarded beyond the same crash or activation failure.
* No LPE awarded. Privilege escalation is not established by the patch.

Negative signals:

* No -2 host-admin penalty applied in the numeric score because the supplied evidence does not fully resolve all possible activation paths. Direct dm-cache setup is normally host-admin controlled, but delegated storage management or privileged autoactivation scenarios are not ruled out.
* No namespace-scoped privilege bonus. Device-mapper metadata activation is not shown to be fully namespace-scoped.

3. Reachability analysis

The direct trigger is crafted dm-cache / dm persistent-data metadata. The vulnerable path is reached when the kernel loads or shadows a dm array block whose on-disk value_size does not match the caller expected value_type.size.

A typical direct setup requires privileged device-mapper control, usually host root or CAP_SYS_ADMIN, to activate dm-cache metadata. However, the supplied input does not fully prove that every practical exposure requires host-admin-equivalent privilege, because crafted block metadata may be supplied to a privileged storage-management service or autoactivation path in some environments. Therefore HostAdminRequired is UNKNOWN rather than YES.

NamespaceScopedPrivilege is NO based on the supplied evidence. No complete namespace-scoped trigger chain is shown.

The issue is not network reachable. It requires local crafted storage metadata and a dm-cache metadata load path. No special race timing is required. No special hardware is required beyond use of the relevant device-mapper / dm-cache metadata path.

4. Primitive and severity interpretation

The exact primitive is an out-of-bounds read caused by a value-size mismatch between the dm array block header and the caller expected element size. The block can be internally consistent under array_block_check(), but the caller later walks it with a different stride.

This is not an ordinary UAF or cleanup-only stale dereference. It is also not a controlled write primitive. The meaningful concern is crafted metadata causing semantic reinterpretation and OOB kernel access in an active storage metadata path.

PrimitiveClass is CLASS_B because there is a concrete kernel memory-safety / semantic interpretation primitive requiring exploitation-leverage review, but no controlled corruption, arbitrary write, demonstrated disclosure, or LPE is established.

The demonstrated consequence is at least local DoS or device activation failure. The speculative consequence is limited confidentiality or integrity impact if additional paths make the OOB read observable or make the misinterpreted metadata affect persistent state, but that is not proven here.

ImportantCandidate is YES because crafted storage metadata plus OOB access in dm-cache metadata loading should not be automatically downgraded without manual review. AutoDowngradeAllowed is NO for the same reason: automatic closure would risk losing a concrete metadata reinterpretation and OOB-read primitive.

Likely operational severity is Actionable Moderate, with Important review warranted if downstream analysis finds disclosure, persistent metadata corruption, or a below-host-admin activation path.

5. One-sentence report phrase

Crafted dm array metadata can pass internal validation with one value size and later be consumed by dm-cache with another value size, causing an out-of-bounds kernel read during metadata loading and requiring manual review for possible DoS or storage metadata impact.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch establishes a concrete crafted-metadata OOB read in an important storage metadata path, and the complete privilege and downstream impact boundaries are not fully resolved.

7. Call-site confidence

Call-site confidence: medium

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

Patch: dm array: reject an array block whose value size is not the caller's
Commit: 7bf4b5cb42a4e27f36bcbc6209d82a5da9c0168c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7bf4b5cb42a4e27f36bcbc6209d82a5da9c0168c

Commit description:

array_block_check() can only compare the header against itself, so a block
with value_size 4 and max_entries 1018 is internally consistent and passes.
dm-cache keeps two arrays -- mappings at 8 bytes and hints at 4 -- and the
roots for both live in the superblock. Point the mappings root at a hint
block and __load_mappings() walks it through an info whose value size is 8,
so element_at() strides 8 bytes over 4-byte entries and reaches offset 8160
of a 4096-byte block.

get_ablock() and __shadow_ablock() are the two places that hold the block
and the caller at once. Reject there when the two value sizes disagree.
Arrays only ever read their own blocks, so this fires on crafted metadata
only.

Fixes: 6513c29 ("dm persistent data: add transactional array")
Suggested-by: Ming-Hung Tsai <mtsai@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Reviewed-by: Ming-Hung Tsai <mtsai@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/md/persistent-data/dm-array.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=7bf4b5cb42a4e27f36bcbc6209d82a5da9c0168c

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

The original Linux kernel CVE announcement for CVE-2026-89573 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89573

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:L/PR:H/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 6.6

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: 3
  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: NO
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).