[CVE-2026-89584][MODERATE 7.0] block: validate user space vectors during extraction

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

CVE: CVE-2026-89584
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: block: validate user space vectors during extraction
Commit: d44a97a3b1c00cc571245124e23e5ceb0a0225a0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d44a97a3b1c00cc571245124e23e5ceb0a0225a0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89584
Analysis date: Sat, 12 Sep 2026 03:16:03 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89584 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89584

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: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-89584	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89584 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-20;CWE-754;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.8';DESCR 'Block direct I/O could build bios from userspace vectors that do not satisfy the target device DMA alignment. Some bio based or stacking drivers may not reject this after submission, so a local caller can reach lower block layers with sub aligned buffer offsets or lengths and cause I/O failure, data corruption, or a kernel availability problem on affected storage stacks. For the CVSS the PR:L is used because triggering requires a local process with permission to issue direct I/O or io_uring I/O to an accessible block device or file, but it does not require full administrator privileges in all deployments. The issue is not network reachable. Impact is mainly local denial of service or storage integrity risk. For the paranoid score, choose the highest still defensible interpretation supported by the bug class and patch context, with preference for manual review sensitivity over autoclosed false negatives.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5)  SKIP CVE-2026-89584 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	OOB INIT DMAorINTERRUPT HARDWARE IO_URING KPANIC MEMORY 	-	-	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4. Validation-only cap would allow at most 4 for conservative analysis and does not change the score.
* Raw paranoid score: 5
* Paranoid score: 5. Validation-only paranoid cap would allow at most 5 and does not change the score.
* Final recommended bucket: **Actionable Moderate**::

2. Signal breakdown

Conservative positive signals:

* +1 Local unprivileged trigger. A local process can plausibly issue direct I/O or io_uring I/O to an accessible file or block object and control user vector alignment without host-admin privilege in all deployments.
* +1 Local high-control kernel data-plane API. The caller controls iovec address, length, and alignment properties that directly affect bio construction and segment extraction.
* +1 Memory layout invariant restoration. The patch restores consistency between user vector addresses, segment lengths, bio_vec layout, and the target device dma_alignment.
* +1 Important filesystem/storage path. The affected code is in generic block direct I/O, iomap direct I/O, bio construction, and iov_iter extraction paths.

Paranoid additional signal:

* +1 Weak indirect corruption or storage-integrity concern. The commit states that some bio-based drivers do not necessarily check the alignment split and stacking drivers do not always handle misalignment after bio submission, so misaligned bios can plausibly cause I/O failure, data corruption, or broader availability problems on affected storage stacks.

Negative signals:

* No -2 host-admin penalty. Host-admin-equivalent privilege is not positively established because ordinary direct I/O to accessible files may be sufficient.
* No -1 race penalty. This is not a timing race.
* No rare subsystem penalty. Generic block and iomap direct I/O are important common kernel paths.
* No hardware-only penalty. Device dma_alignment matters, but no rare physical-only hardware requirement is established.

Important non-awarded signals:

* RealUAF not awarded. No stale object or post-lifetime use is shown.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Concrete kernel OOB write not demonstrated.
* Concrete repeated release or refcount mutation not present.
* Confidentiality not awarded because no readback or disclosure path is shown.
* Integrity is not awarded as a strong security-boundary signal because unauthorized modification of another principal protected data is not established. The paranoid point only reflects storage integrity concern.
* Reliable kernel crash not awarded because the patch does not demonstrate a concrete panic or fault path.
* Remote reachability not established.
* ImportantCandidate not set because there is no Class A or Class B primitive.

3. Reachability analysis

The most plausible attacker is a local process that can issue direct I/O or io_uring I/O against an accessible file or block device. The attacker can choose user buffer addresses and lengths and can therefore create sub-aligned vectors.

Host administrator privilege is not positively required for the complete vulnerable operation because direct I/O may be available on files owned or writable by an ordinary user. Raw block-device access may require elevated privileges in many deployments, but that is not the only relevant path.

Namespace-scoped privilege is not the core issue here. No complete namespace-scoped capability chain is required or established.

No prior privileged setup is clearly required beyond the existence of a filesystem or block stack that permits direct I/O. Specific impact depends on the lower block driver or stacking driver behavior after receiving misaligned bios.

There is no network trigger. There is no race. No special rare hardware is established, although the practical impact depends on device dma_alignment and block-stack behavior.

4. Primitive and severity interpretation

The exact primitive is missing validation of user-space vector memory alignment during bio construction. Misaligned vectors may be forwarded to lower block layers even when the target device requires stronger DMA alignment.

This is not a UAF, not a repeated release, not a controlled reclaim, and not an arbitrary kernel read or write. The patch primarily rejects invalid input early with EINVAL and releases pages pinned before an early failure.

PrimitiveClass is CLASS_C because the demonstrated issue is an invalid-state or validation failure that may lead to I/O errors, storage corruption risk, or availability problems, but no independently useful memory-corruption or lifetime primitive is established.

The demonstrated consequence is unsafe submission of misaligned bio segments to drivers that may not correctly handle the condition after submission. The speculative consequence is broader data integrity or availability impact on particular storage stacks. That possibility justifies Actionable Moderate triage and manual review, but not ImportantCandidate status without stronger evidence.

AutoDowngradeAllowed is YES because no Class A or Class B primitive, ownership violation, authorization bypass, UAF, or controlled corruption is established. However, the score is still actionable because the affected path is generic storage I/O and the real impact is driver-stack dependent.

Likely operational severity is Moderate, with manual validation recommended for products using affected direct I/O paths and stacking block drivers.

5. One-sentence report phrase

Block direct I/O could build bios from user vectors that violate device DMA alignment, allowing a local caller with access to direct I/O or io_uring I/O to cause I/O failure, possible storage integrity problems, or availability impact on affected block stacks.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because the patch touches generic block direct I/O and iomap bio construction, and the real-world impact depends on whether affected lower bio-based or stacking drivers mishandle misaligned bios after submission.

7. Call-site confidence

Call-site confidence: medium

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

Patch: block: validate user space vectors during extraction
Commit: d44a97a3b1c00cc571245124e23e5ceb0a0225a0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d44a97a3b1c00cc571245124e23e5ceb0a0225a0

Commit description:

The bio-based drivers don't necessarily check the alignment split, and
stacking block drivers don't always handle a misalignment detected after
submitting the bio. Validate user vectors against the device's
dma_alignment as the bio is built from the iov_iter, rejecting
misaligned early with -EINVAL.

Cc: stable@vger.kernel.org
Fixes: 5ff3f74 ("block: simplify direct io validity check")
Fixes: 7eac331 ("iomap: simplify direct io validity check")
Reviewed-by: Hannes Reinecke <hare@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Link: https://patch.msgid.link/20260720201057.1862857-6-kbusch@meta.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  block/bio.c
  block/blk-map.c
  block/fops.c
  fs/iomap/direct-io.c
  include/linux/bio.h
  include/linux/uio.h
  lib/iov_iter.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=d44a97a3b1c00cc571245124e23e5ceb0a0225a0

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

The original Linux kernel CVE announcement for CVE-2026-89584 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89584

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:L/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: 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).