[CVE-2026-74365][MODERATE 7.0] nvdimm/btt: Handle preemption in BTT lane acquisition [ Upstream

[CVE-2026-74365][MODERATE 7.0] nvdimm/btt: Handle preemption in BTT lane acquisition [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74365
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: nvdimm/btt: Handle preemption in BTT lane acquisition [ Upstream
Commit: fd7a97b2514cfc4b4cc067a27dd39bde2a8b1735
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fd7a97b2514cfc4b4cc067a27dd39bde2a8b1735
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74365
Analysis date: Sun, 16 Aug 2026 02:49:43 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in nvdimm BTT lane acquisition can allow concurrent use of the same lane during write I/O, causing silent persistent data corruption and possible storage availability impact for local users with access to a configured BTT-backed device.

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

The original Linux kernel CVE announcement for CVE-2026-74365 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74365

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: YES

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

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

CVE-2026-74365	MODERATE	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:H/A:H';CWE-362;CWE-667;CWE-662;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L';BEST CVSS score: '6.5';DESCR 'A race in nvdimm BTT lane acquisition can allow two tasks on the same CPU to use the same BTT lane concurrently after lanes became preemptible. The per CPU recursion count can be observed as non zero by another task and that task can bypass locking, which can corrupt per lane metadata or workspace state during BTT write I/O. For the CVSS the PR:L is used because triggering requires local ability to issue writes through a configured BTT namespace or a filesystem backed by that device, but it does not normally require full administrator privileges once write access exists. The issue is not network reachable. Impact is primarily persistent data integrity loss and possible denial of service if corrupted BTT or filesystem metadata makes data unavailable.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	OOB LOCK INIT RACE LOG HARDWARE TEST MEMORY  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	YES	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local user or process with write access to a configured BTT namespace or filesystem backed by it can issue BTT I/O. Full administrator privileges are not necessarily required after the device is exposed.

* Filesystem/storage metadata corruption reachable by an unprivileged local user: +1
  The commit explicitly reports BTT write data mismatches and silent data corruption caused by concurrent lane use.

* Important filesystem/storage path: +1
  BTT is a persistent-memory block translation layer. Corruption can affect persistent storage contents, not just transient kernel state.

* Integrity impact plausible: +1
  Silent corruption of BTT per-lane metadata or workspace state during writes directly supports persistent data integrity impact.

* Availability impact realistic: +1
  Persistent data or metadata corruption can make stored data unavailable or require filesystem or namespace repair. This is more than a transient warning or local assertion.

Possible subtractive signal for conservative score:

* Rare or configuration-dependent subsystem: -1
  NVDIMM BTT is not a broad default path on most systems and requires configured persistent-memory BTT usage.

Not awarded:

* Remote reachable: +0
  No network trigger is indicated.

* Generic kernel memory corruption: +0
  The patch shows a synchronization race causing storage data corruption, not UAF, OOB write, double free, arbitrary write, or object lifetime corruption.

* Privilege escalation plausible: +0
  No concrete LPE primitive is shown. The realistic impact is storage integrity loss and possible availability impact.

* Hard race penalty: 0
  Although this is a race, the issue was reproduced by the ndctl btt-check test and follows naturally from preemption plus concurrent BTT I/O, so I would not strongly discount it as an impractical timing-only bug.

## 3. Reachability analysis

The bug is triggered through local BTT I/O on an affected NVDIMM BTT namespace. A user does not need host-root privileges if they already have write access to a filesystem or block device backed by the BTT namespace, but creating or configuring such namespaces is normally administrative.

Namespaces or containers may matter only if the BTT-backed storage is delegated into the container or exposed to a less privileged workload. The vulnerable path is not network reachable by itself. The affected subsystem is not commonly enabled on general-purpose systems, but on systems using NVDIMM BTT it is in the ordinary write path.

Call-site confidence: high. The patch states that the only in-tree caller is BTT submit_bio via btt_read_pg and btt_write_pg, and the commit directly identifies write I/O data mismatches.

## 4. Severity interpretation

This behaves stronger than an ordinary Moderate correctness fix because it can cause silent persistent data corruption. It does not currently look like an Important-class memory corruption or privilege-escalation bug, because the patch does not show a kernel object lifetime primitive, attacker-controlled overwrite, type confusion, or arbitrary write.

The practical severity is therefore Actionable Moderate at minimum. Manual review is justified because persistent storage integrity corruption is security-relevant even without code execution.

## 5. One-sentence report phrase

A race in nvdimm BTT lane acquisition can allow concurrent use of the same lane during write I/O, causing silent persistent data corruption and possible storage availability impact for local users with access to a configured BTT-backed device.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is not a simple crash-only bug. It affects persistent storage integrity and was reproduced as silent data corruption, so it should not be auto-closed even though no direct privilege-escalation primitive is shown.

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

Patch: nvdimm/btt: Handle preemption in BTT lane acquisition [ Upstream
Commit: fd7a97b2514cfc4b4cc067a27dd39bde2a8b1735
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fd7a97b2514cfc4b4cc067a27dd39bde2a8b1735

Changed files:
  drivers/nvdimm/nd.h
  drivers/nvdimm/region_devs.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=fd7a97b2514cfc4b4cc067a27dd39bde2a8b1735

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

The original Linux kernel CVE announcement for CVE-2026-74365 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74365

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:H/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:H
  The Best / paranoid CVSS score: 6.5

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: NO
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).