[CVE-2026-93073][MODERATE REGULAR] dax: read holder_ops once in dax_holder_notify_failure() [ Upstream

[CVE-2026-93073][MODERATE REGULAR] dax: read holder_ops once in dax_holder_notify_failure() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-93073
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: dax: read holder_ops once in dax_holder_notify_failure() [ Upstream
Commit: 1661b9bf78def01a8c96409569772d9b2592f4ba
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1661b9bf78def01a8c96409569772d9b2592f4ba
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93073
Analysis date: Thu, 17 Sep 2026 21:59:21 -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-2026-93073 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93073

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-2026-93073	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-93073 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-362;CWE-367;**CWE-476;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A race in dax_holder_notify_failure() can occur because holder_ops is checked and then read again for the notify_failure() callback while fs_put_dax() may concurrently clear the same field. The first read can observe a valid pointer and the second read can observe NULL, causing a NULL function pointer dereference and a kernel crash. For the CVSS the PR:L is used in the paranoid score because some deployments may delegate DAX device teardown or fault handling to a reduced privilege service account or container root, although typical direct triggering requires administrative control. The issue is not network reachable and requires local interaction with the DAX failure notification or holder teardown path. Impact is denial of service only because the patch supports a NULL dereference race and does not show a UAF, OOB access, information leak, or arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	SIMPLEFIX RACE IMPROVEONLY  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	YES	NO	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
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

Conservative signals:

* +1 Reliable kernel crash / strong DoS: the race can make the second read of `holder_ops` return NULL and then dereference NULL through `ops->notify_failure`, causing kernel fault or panic.
* +1 Weak indirect pointer consistency issue: the bug is a check/use mismatch on an operations pointer used for an indirect callback path, but the demonstrated sink is NULL dereference only.
* +1 Important storage/DAX path: the affected code is in DAX failure notification, which is part of storage and memory-failure handling.
* -1 Hard race / special timing: the issue requires `fs_put_dax()` to clear `holder_ops` between the NULL check and the callback dereference.

Paranoid difference:

* The paranoid score does not apply the -1 timing reduction, because the patch establishes a real concurrent unsynchronized reader/writer pattern and repeated teardown/failure attempts may make the window more reachable in some test or managed environments.

Non-awarded signals:

* RealUAF not awarded: the patch establishes a NULL reload race, not use-after-free of `holder_ops`.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity impact not awarded.
* Strong LPE or strong exploitation leverage not awarded.
* Concrete repeated release/refcount not present.
* Extra Availability not awarded because the same crash is already counted.
* Remote reachability not established.
* Namespace-scoped privilege not established.

3. Reachability analysis

The complete trigger appears to require two concurrent conditions: `dax_holder_notify_failure()` running while `fs_put_dax()` clears the holder operations pointer. This is a local kernel/device/storage management path rather than a packet or ordinary remote input path.

Below-host-admin reachability is not established from the supplied patch. Directly controlling DAX holder teardown, filesystem/DAX device lifecycle, or memory-failure notification usually suggests administrative or managed service involvement, but the evidence does not prove a host-admin-equivalent requirement for all deployments. Therefore `HostAdminRequired=UNKNOWN`.

No evidence shows that the complete trigger chain is namespace-scoped. DAX device and filesystem holder lifecycle are not ordinary attacker-created namespace-local objects in the supplied context. `NamespaceScopedPrivilege=NO`.

No prior public-network exposure is indicated. Special DAX-capable storage or persistent-memory style configuration may be relevant, but no rare-hardware penalty is applied because the patch alone does not prove a physical-only or unusually rare prerequisite.

Race repeatability is uncertain. The conservative score treats the window as narrow. The paranoid score keeps the race concern but does not subtract the timing point.

4. Primitive and severity interpretation

The exact primitive is a race / TOCTOU on `dax_dev->holder_ops`: one read checks for non-NULL, while a later reload may observe NULL after `fs_put_dax()` clears the pointer. The resulting operation is a NULL function pointer structure dereference, not a confirmed stale freed object use.

This is not a concrete UAF. It is not a repeated lifetime/refcount mutation. It is not a controlled callback hijack, because the patch only shows the pointer becoming NULL, not attacker-controlled replacement contents.

Primitive class is `CLASS_C`: demonstrated behavior is crash/DoS through invalid state and NULL dereference. The demonstrated consequence is kernel crash or panic. The speculative consequence would require an unproven stronger primitive such as controlled replacement of the operations table, which is not supported here.

`ImportantCandidate=NO` because there is no concrete memory corruption, security-boundary bypass, controlled reclaim, repeated refcount mutation, or privilege-escalation path. `AutoDowngradeAllowed=YES` because the established issue is a constrained crash-only race.

Likely operational severity is ordinary Moderate to borderline Moderate depending on how easily the affected DAX failure and teardown paths can be exercised in the evaluated product.

5. One-sentence report phrase

A race in `dax_holder_notify_failure()` can reload `holder_ops` after `fs_put_dax()` clears it, causing a NULL dereference in the DAX failure notification callback path and resulting in a local kernel crash DoS.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

The issue is probably DoS-only, but manual review is useful to confirm product-specific reachability of DAX failure notification and whether any delegated service can trigger the teardown/failure race below host-admin privilege.

7. Call-site confidence

Call-site confidence: medium

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

Patch: dax: read holder_ops once in dax_holder_notify_failure() [ Upstream
Commit: 1661b9bf78def01a8c96409569772d9b2592f4ba
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1661b9bf78def01a8c96409569772d9b2592f4ba

Changed files:
  drivers/dax/super.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=1661b9bf78def01a8c96409569772d9b2592f4ba

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

The original Linux kernel CVE announcement for CVE-2026-93073 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93073

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:H/UI:N/S:U/C:N/I:N/A:H
  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).