[CVE-2026-89574][MODERATE REGULAR] dm array: validate array block headers on read

[CVE-2026-89574][MODERATE REGULAR] dm array: validate array block headers on read

[AL-KERNEL]

CVE: CVE-2026-89574
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: dm array: validate array block headers on read
Commit: 67adda7ed5da3e3b64f5b9021a02c21fb374fd9c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=67adda7ed5da3e3b64f5b9021a02c21fb374fd9c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89574
Analysis date: Sat, 12 Sep 2026 03:57:34 -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.

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

The original Linux kernel CVE announcement for CVE-2026-89574 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89574

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.

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

CVE-2026-89574	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89574 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H';CWE-125;*CWE-20;CWE-130;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.6';DESCR 'dm-array did not fully validate on-disk array block header fields before using them during metadata traversal. A crafted or corrupted metadata block can set nr_entries or max_entries inconsistently with value_size and the real block capacity, causing dm_array_cursor_next() and element_at() to read past the dm-bufio buffer during device-mapper metadata activation. For the CVSS the PR:H is used because reliable triggering normally requires administrative control over device-mapper activation or write access to the metadata block device. The issue is not directly network reachable and is triggered through local storage metadata handling rather than packet traffic. Impact is at least denial of service via kernel crash. In the paranoid case, limited confidentiality or integrity impact is kept because the bug is an out-of-bounds read in kernel metadata parsing, but no arbitrary write primitive is evident.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	DISK LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	NO	NO	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
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. The paranoid score is emitted as the final ActionableScore because the dm-array OOB read is in persistent storage metadata parsing and the values read during traversal may influence cache mapping reconstruction, but there is no demonstrated write primitive, UAF, authorization bypass, or LPE path.

2. Signal breakdown

Conservative signals:

* +1 Concrete read-only OOB primitive. `nr_entries` is taken from on-disk metadata and can exceed the real array block capacity, causing `dm_array_cursor_next()` and `element_at()` to read past the dm-bufio buffer.
* +1 Reliable kernel crash / strong DoS. The patch description directly says the read walks off the dm-bufio buffer during activation, which plausibly leads to kernel fault or device activation failure.
* +1 Important storage metadata path. The affected code is device-mapper persistent metadata used by dm-cache style activation paths.
* +1 Metadata layout invariant violation. The bug is specifically inconsistent `value_size`, `max_entries`, and `nr_entries` versus the real block size, which controls pointer arithmetic and traversal bounds.
* -2 Host-admin-equivalent requirement. Reliable triggering normally requires creating or activating the affected device-mapper target or writing crafted metadata to the metadata block device.

Paranoid additional signal:

* +1 Paranoid storage-metadata consumption concern. The OOB read occurs while loading mappings, so malformed metadata may cause invalid mapping reconstruction or other active storage-state effects before failure. This is still treated as weak unresolved behavior, not as arbitrary read/write.

Important non-awarded signals:

* RealUAF not awarded. No stale pointer, refcount lifetime violation, double release, or post-free use is established.
* CLASS_A not awarded. No controlled overwrite, controlled reclaim, authorization bypass, COW violation, privileged resource theft, or demonstrated LPE exists.
* Confidentiality not awarded. The OOB read is internal to kernel metadata traversal and no user-visible disclosure path is shown.
* Integrity not awarded as a strong primitive. Although mapping reconstruction is affected, no unauthorized write to protected data or controlled metadata overwrite primitive is established.
* Remote reachability not awarded. The trigger is local storage metadata handling, not packet processing.
* Extra availability not awarded. The same crash or activation failure is not double-counted.
* Concrete repeated release/refcount signal not awarded. There is no first release that can end object lifetime and no second lifetime mutation on the same dangling reference.

3. Reachability analysis

The practical trigger is a crafted or corrupted dm-array metadata block that is read during device-mapper metadata activation. The commit specifically mentions `dm_cache_load_mappings()` driving the traversal once per cache block at activation.

The complete trigger normally requires host-admin-equivalent control because an attacker must either activate the relevant dm target or supply/write the metadata block device contents. This is why `HostAdminRequired=YES` is used.

No evidence shows that the complete operation is reachable through attacker-created user namespaces or namespace-scoped capabilities. `NamespaceScopedPrivilege=NO` is therefore appropriate for the supplied evidence.

No network path is established. No special physical hardware is required beyond use of affected device-mapper metadata. No race is involved.

4. Primitive and severity interpretation

The exact primitive is an out-of-bounds read from a dm-bufio buffer caused by trusting unvalidated on-disk structural fields in an array block header.

This is not active-object UAF and not fixed stale storage. It is malformed persistent metadata causing unguarded pointer arithmetic past the validated buffer.

The demonstrated consequence is kernel crash, activation failure, or storage metadata handling failure. The speculative consequence is limited invalid mapping interpretation during activation, but no patch-supported arbitrary write, controlled kernel read disclosure, privilege escalation, or security-boundary bypass is established.

PrimitiveClass is `CLASS_C` because the established behavior is primarily OOB read / invalid-state / DoS without an independently useful corruption primitive.

ImportantCandidate is `NO` because the issue is host-admin-gated, has no UAF, no write primitive, no controlled reclaim, and no demonstrated boundary bypass. Manual review is still recommended because it is a real kernel OOB read in persistent storage metadata parsing.

AutoDowngradeAllowed is `YES` because the issue can reasonably be treated as ordinary or borderline Moderate after triage, assuming no additional advisory evidence demonstrates a lower-privilege trigger or stronger storage-integrity consequence.

Likely operational severity: ordinary Moderate to borderline actionable Moderate, mainly local privileged DoS.

5. One-sentence report phrase

A malformed dm-array metadata block can bypass structural header validation and make `dm_array_cursor_next()` read past the dm-bufio buffer during device-mapper activation, causing a local host-admin-triggered kernel DoS with no demonstrated UAF, write primitive, network reachability, or privilege escalation.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a concrete kernel OOB read in storage metadata parsing, but the available evidence indicates host-admin-triggered DoS rather than an Important-grade corruption or authorization primitive.

7. Call-site confidence

Call-site confidence: medium

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

Patch: dm array: validate array block headers on read
Commit: 67adda7ed5da3e3b64f5b9021a02c21fb374fd9c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=67adda7ed5da3e3b64f5b9021a02c21fb374fd9c

Commit description:

array_block_check() validates blocknr and csum and nothing else, while
node_check(), next to it, has bounded the structural fields since both
were written. dm_array_cursor_next() takes its loop bound from the
on-disk nr_entries and element_at() is unguarded pointer arithmetic, so
a count larger than the block holds keeps the cursor in one block while
the index grows past it and the read walks off the dm-bufio buffer --
dm_cache_load_mappings() drives it once per cache block at activation.

Check the header against itself: reject a zero value_size, require
max_entries to equal calc_max_entries() for that value_size and block
size, and require nr_entries to fit. Equality rather than an upper bound,
since a count below the real capacity trips BUG_ON() in fill_ablock() and
trim_ablock(). Metadata dm-array writes satisfies all three.

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=67adda7ed5da3e3b64f5b9021a02c21fb374fd9c

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

The original Linux kernel CVE announcement for CVE-2026-89574 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89574

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.6

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: 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).