[CVE-2026-89457][MODERATE REGULAR] s390/dasd: Guard sysfs discipline callbacks against unallocated private data

[CVE-2026-89457][MODERATE REGULAR] s390/dasd: Guard sysfs discipline callbacks against unallocated private data

[AL-KERNEL]

CVE: CVE-2026-89457
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: s390/dasd: Guard sysfs discipline callbacks against unallocated private data
Commit: 536407b272402af679155910d7fdeeb4834eefb9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=536407b272402af679155910d7fdeeb4834eefb9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89457
Analysis date: Fri, 11 Sep 2026 23:19:00 -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-2026-89457 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89457

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-2026-89457	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89457 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-362;CWE-665;BEST CVSS score: '4.7';DESCR 'A NULL pointer dereference in s390 DASD ECKD sysfs discipline callbacks can occur because the discipline may be assigned before device private data is allocated during dasd_generic_set_online. A local user can trigger the bug by reading a world readable sysfs attribute in that timing window, causing the callback to dereference device private while it is still NULL and panic the kernel. For the CVSS the PR:L is used because the attacker needs local user access to read the sysfs attribute, but does not need administrative privileges for the read itself. The issue is not network reachable and depends on a race with device online initialization on affected s390 DASD systems. Impact is denial of service via kernel crash. Confidentiality and integrity impact are not assigned because the observed primitive is a NULL pointer dereference rather than UAF, OOB access, information disclosure, or arbitrary write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	DANGER SIMPLEFIX HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	NO	NO	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
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 changed the score.

2. Signal breakdown

Positive signals:

* +1 Local unprivileged trigger. The supplied description explicitly says an unprivileged read of a world-readable sysfs attribute can hit the vulnerable window.
* +1 Reliable kernel crash / strong DoS. The described consequence is NULL pointer dereference and panic.
* +1 Weak / indirect corruption candidate. The primitive is an invalid NULL dereference of device->private through DASD discipline callbacks, not a UAF or controlled memory corruption.

Negative signals:

* -1 Conservative hard timing window. The read must occur after the discipline is assigned but before check_device() allocates device->private during dasd_generic_set_online().
* 0 Paranoid timing penalty withheld. Repeated reads of world-readable sysfs attributes during online initialization could make the timing more reachable than a one-shot uncontrollable race.

Important non-awarded signals:

* RealUAF not awarded. The object is not freed and reused. The bug is an unallocated private pointer dereference.
* Concrete repeated release/refcount not awarded. No first release, surviving dangling reference, or second lifetime mutation is present.
* Controlled reclaim not demonstrated.
* Arbitrary or directed write not demonstrated.
* Confidentiality and integrity not awarded. There is no disclosure path, UAF, OOB access, arbitrary write, or authorization bypass.
* Extra availability not awarded. The panic is already counted as the DoS signal.
* Rare hardware penalty not applied. The issue is s390 DASD specific, but the affected deployment is exactly that environment and this alone should not erase an unprivileged crash trigger.

3. Reachability analysis

The attacker operation is a local read of world-readable DASD sysfs attributes. The supplied evidence supports below-host-admin reachability for the read itself, so HostAdminRequired=NO.

The complete trigger also depends on a concurrent device online initialization window in dasd_generic_set_online(). Bringing the DASD device online is normally a privileged device-management operation or an administrator/udev driven event, so the attacker may need to race an existing online transition rather than fully create the condition alone.

No namespace-scoped capability path is involved. NamespaceScopedPrivilege=NO.

There is no network reachability. The issue is local sysfs control/inspection plane behavior.

Special hardware is required in the practical sense because this is s390 DASD ECKD code, but this is treated as deployment scope rather than a strong score-reducing signal.

Race repeatability is uncertain. The vulnerable read can likely be retried, but the vulnerable allocation window is narrow and tied to online initialization.

4. Primitive and severity interpretation

The exact primitive is a NULL pointer dereference of device->private in DASD ECKD discipline callbacks.

This is not active structured UAF and not fixed stale storage. It is an initialization ordering race where callbacks become reachable before private data exists.

The demonstrated consequence is local kernel panic / DoS.

Speculative consequences beyond crash are not supported by the patch. There is no evidence of controlled replacement, stale post-lifetime object use, refcount mutation, arbitrary write, callback hijack, disclosure, or privilege escalation.

PrimitiveClass=CLASS_C because the demonstrated behavior is crash/DoS from invalid state rather than a meaningful corruption or ownership primitive.

ImportantCandidate=NO because the patch supports NULL dereference DoS only and does not leave unresolved Important-grade memory corruption leverage.

AutoDowngradeAllowed=YES because there is no UAF, no repeated lifetime mutation, no controlled corruption, and no security-boundary bypass. Manual review is still recommended because the trigger is unprivileged local sysfs access and the race affects kernel panic behavior.

Likely operational severity is borderline Moderate: serious for affected s390 DASD systems, but not an Important-class kernel exploitation primitive based on supplied evidence.

5. One-sentence report phrase

A local unprivileged read of world-readable s390 DASD ECKD sysfs attributes can race device online initialization and dereference unallocated device private data, causing a NULL pointer dereference and kernel panic.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: unprivileged local sysfs reachability and kernel panic are established, but the primitive is NULL dereference only and does not show UAF, memory corruption leverage, information disclosure, integrity impact, or privilege escalation.

7. Call-site confidence

Call-site confidence: high

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

Patch: s390/dasd: Guard sysfs discipline callbacks against unallocated private data
Commit: 536407b272402af679155910d7fdeeb4834eefb9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=536407b272402af679155910d7fdeeb4834eefb9

Commit description:

Several sysfs show/store handlers call a discipline callback that
dereferences device->private, either directly or through the
DASD_DEFINE_ATTR() macro. During dasd_generic_set_online() the discipline
is assigned before check_device() allocates device->private, so an
unprivileged read of one of these world-readable attributes in that window
dereferences a NULL pointer and panics.

Guard the dereference inside each callback that actually touches
device->private.

Fixes: c729696 ("s390/dasd: Recognise data for ESE volumes")
Cc: stable@vger.kernel.org
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://patch.msgid.link/20260805111612.1285190-4-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/s390/block/dasd_eckd.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=536407b272402af679155910d7fdeeb4834eefb9

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

The original Linux kernel CVE announcement for CVE-2026-89457 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89457

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 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).