[CVE-2026-89586][LOW] ata: libata-scsi: fix DSM TRIM for sector sizes larger than 2048 bytes

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

CVE: CVE-2026-89586
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ata: libata-scsi: fix DSM TRIM for sector sizes larger than 2048 bytes
Commit: 04e2befe25792f2e90097f284d7e86fc6bcfe928
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=04e2befe25792f2e90097f284d7e86fc6bcfe928
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89586
Analysis date: Sat, 12 Sep 2026 05:39:02 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
ATA DSM TRIM handling incorrectly sized the descriptor from the logical sector size, causing discard to fail on devices with sector sizes larger than 2048 bytes, with low availability impact and no demonstrated memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-89586 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89586

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: LOW
Manual review required: NO

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
======================================================================

CVE-2026-89586	LOW	https://www.kernelcve.org/list/?q=CVE-2026-89586 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:L/UI:N/S:U/C:N/I:N/A:L';CWE-682;CWE-754;CWE-693;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '3.3';DESCR 'ATA DSM TRIM translation for SCSI WRITE SAME with UNMAP used the logical sector size when building and validating the TRIM descriptor. On devices with sector sizes larger than 2048 bytes, such as 4Kn drives, the generated descriptor was capped by the 2048 byte staging buffer while the caller expected the full logical sector size, so every discard request failed with a parameter length error and repeated WARN output. For the CVSS the PR:L is used for the paranoid score because a local user may indirectly cause filesystem discard requests on systems mounted with online discard, although direct BLKDISCARD or fstrim is usually administrative. The issue is not network reachable. Impact is low availability due to broken TRIM / discard behavior and possible warning spam, with no evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	WARNONLY HARDWARE LINUS 	NO	NO	checked

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

ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

## 1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap changed the score.

## 2. Signal breakdown

Conservative signals:

* +1 Availability impact realistic: TRIM / discard is completely broken on affected ATA devices with logical sector size larger than 2048 bytes, and repeated WARN output may occur.
* 0 Primitive: no UAF, OOB access, double free, refcount misuse, stale pointer, arbitrary write, or security-boundary bypass is established.
* 0 WARN_ON: WARN output is present, but no kernel panic or host-wide crash is established.
* 0 No privilege penalty: host-admin-equivalent triggering is not fully established for all practical paths, so no unsupported -2 is applied.

Paranoid additional signal:

* +1 Possible below-host-admin indirect trigger: on systems mounted with online discard, an ordinary local user may indirectly cause discard requests through normal filesystem activity. This is deployment-dependent and does not create a stronger primitive.

Important non-awarded signals:

* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Real UAF not demonstrated.
* Repeated release or refcount mutation not demonstrated.
* Remote reachability not established.
* C/I impact not awarded because the patch shows a sizing / translation logic bug that rejects valid TRIM requests, not disclosure or unauthorized modification.
* Extra availability not awarded because there is no distinct persistent host-wide DoS beyond broken discard functionality and WARN noise.
* Manual-review preserving primitive not established.

## 3. Reachability analysis

The directly affected operation is SCSI WRITE SAME with UNMAP translated into ATA DSM TRIM by libata-scsi. Direct user-triggered discard operations such as BLKDISCARD or fstrim are usually administrative, but the evidence does not prove that host-admin-equivalent privilege is the only possible path.

A lower-privileged local user may indirectly cause discard if the filesystem is configured for online discard, because normal file deletion or block release can lead to discard requests. That depends on prior system configuration and filesystem behavior, so HostAdminRequired is UNKNOWN rather than YES or NO.

The issue is not network reachable. No namespace-scoped privilege path is involved. Affected systems need an ATA device with a logical sector size larger than 2048 bytes, such as some 4Kn devices, and DSM TRIM / discard support.

No race is involved. No special timing is required.

## 4. Primitive and severity interpretation

The exact primitive is a logic and sizing mismatch in DSM TRIM descriptor construction. The old code used the SCSI device logical sector size as the descriptor length, while the ATA DSM TRIM payload should be a 512-byte page independent of logical sector size. For devices with sector size larger than the 2048-byte staging buffer, the descriptor length comparison always failed and all TRIM requests were rejected.

This is not active structured UAF and not fixed stale storage. It is not cleanup/destructor lifetime misuse. No concrete repeated release/refcount operation exists.

PrimitiveClass=NONE because the patch establishes broken functionality, not kernel memory corruption or authorization bypass.

Demonstrated consequence: valid discard requests fail and may generate repeated WARN output.

Speculative consequence: long-term operational degradation due to disabled TRIM on affected storage, but not privilege escalation or data exposure.

ImportantCandidate=NO because there is no concrete corruption, ownership violation, security boundary bypass, or unresolved lifetime primitive.

AutoDowngradeAllowed=YES because this is a low-actionability functional storage bug with no established security primitive.

Likely operational severity: Low to ordinary Moderate, depending on how important discard functionality is for the affected deployment.

## 5. One-sentence report phrase

ATA DSM TRIM handling incorrectly sized the descriptor from the logical sector size, causing discard to fail on devices with sector sizes larger than 2048 bytes, with low availability impact and no demonstrated memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the patch and call path show a functional TRIM / discard failure with WARN output, but no concrete security primitive that would justify Important-class review.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: ata: libata-scsi: fix DSM TRIM for sector sizes larger than 2048 bytes
Commit: 04e2befe25792f2e90097f284d7e86fc6bcfe928
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=04e2befe25792f2e90097f284d7e86fc6bcfe928

Commit description:

ata_scsi_write_same_xlat() translates a SCSI WRITE SAME command with the
UNMAP bit set into an ATA DATA SET MANAGEMENT TRIM command.  The TRIM
descriptor is built by ata_format_dsm_trim_descr() into the 2048-byte
ata_scsi_rbuf staging buffer, and the number of bytes copied is compared
against the logical sector size by the caller:

	size = ata_format_dsm_trim_descr(scmd, trmax, block, n_block);
	if (size != len)		/* len == sdp->sector_size */
		goto invalid_param_len;

ata_format_dsm_trim_descr() clamps the copy length to ATA_SCSI_RBUF_SIZE
(2048).  On a device whose logical sector size exceeds that (e.g. a 4Kn
device, where sector_size == 4096) the function can never return more than
2048, while the caller expects it to return sector_size.  The comparison
therefore always fails, so every TRIM is rejected with "Parameter list
length error" and WARN_ON() splats on each attempt.  TRIM / discard is
thus completely broken on such devices.

The descriptor was incorrectly sized from the logical sector size.  A DSM
TRIM payload is a list of 512-byte pages, each holding up to
ATA_MAX_TRIM_RNUM (64) LBA Range Entries, and is independent of the logical
sector size.  The Block Limits VPD page already advertises a single such
page as the maximum WRITE SAME length (65535 * ATA_MAX_TRIM_RNUM logical
blocks), so the block layer never sends a request that needs more than one
page.

Emit exactly one 512-byte page, independent of the logical sector size,
and transfer only that page (COUNT == 1).  For a 512-byte-sector device
this is unchanged; devices with larger logical sectors now work instead of
failing every TRIM.

Reviewed-by: Hannes Reinecke <hare@kernel.org>
Fixes: ef2d739 ("libata: SCT Write Same / DSM Trim")
Cc: stable@vger.kernel.org
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/ata/libata-scsi.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=04e2befe25792f2e90097f284d7e86fc6bcfe928

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

The original Linux kernel CVE announcement for CVE-2026-89586 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89586

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:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 3.3

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: 1
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).