[CVE-2026-53064][LOW] dm cache: fix null-deref with concurrent writes in passthrough mode [ Upstream

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

CVE: CVE-2026-53064
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: dm cache: fix null-deref with concurrent writes in passthrough mode [ Upstream
Commit: 01264a6a3a3ad7ac1d73443299cd5a9568002454
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=01264a6a3a3ad7ac1d73443299cd5a9568002454
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53064
Analysis date: Fri, 26 Jun 2026 14:29:27 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like. Not Actionable Moderate
Manual review required: NO

Summary:
A NULL pointer dereference in dm-cache passthrough invalidation can be triggered by concurrent writes to the same cached block, causing a local kernel crash DoS under a specific device-mapper cache configuration.

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

The original Linux kernel CVE announcement for CVE-2026-53064 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53064

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.

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

CVE-2026-53064	LOW	CHECK	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-703;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 NULL pointer dereference can occur in the dm-cache target when passthrough mode invalidates a cached block while concurrent writes hit the same cached block. If the bio prison cell lock path fails, mg cell remains NULL but invalidate_complete may still try to unlock and free that cell, causing a kernel crash. For the CVSS the PR:L is used in the paranoid score because a reduced-capability root, service account, or delegated block-device writer may be able to submit concurrent writes once the dm-cache device already exists. The issue is not network reachable and requires local access to the affected block device and a specific dm-cache passthrough configuration. Impact is denial of service via kernel oops or panic. No confidentiality or integrity impact is assigned because the observed primitive is a NULL pointer dereference, not UAF, OOB access, information disclosure, or arbitrary write.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like. Not Actionable Moderate (with actual score 1) 	MAYBE	WRITE KASAN OOB NULLPTR DISK ERRORPATH HARDWARE LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like. Not Actionable Moderate**::

## 2. Signal breakdown

Conservative interpretation:

* Reliable kernel crash / strong DoS: +1. The patch fixes a direct NULL pointer dereference in `dm_cell_unlock_v2()` via `mg->cell == NULL`.
* Important filesystem/storage path: +1. The bug is in the device-mapper cache target, a block storage path.
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2. Creating, suspending, reloading, and switching a dm-cache device to passthrough mode normally requires administrative privileges.
* Rare/configuration-dependent path: -1. Triggering requires dm-cache, passthrough mode, an already cached block, invalidation, and concurrent writes to the same cached block.
* Hard/special race condition: effectively 0 or -1. It is a race, but the reproducer suggests it can be triggered with normal concurrent write load once the special setup exists.

Paranoid interpretation:

* Local unprivileged trigger: +1. If an already configured dm-cache block device is writable by a reduced-privilege service account, container root, or delegated storage workload, the final concurrent write trigger may not require full host-root.
* Reliable kernel crash / strong DoS: +1.
* Important filesystem/storage path: +1.
* Rare/configuration-dependent path: -1.

No memory corruption score is added. The demonstrated primitive is NULL dereference, not UAF, double-free, OOB write, arbitrary write, or page-cache corruption.

## 3. Reachability analysis

In typical deployments, only an administrator can create and reconfigure the dm-cache mapping and switch it into passthrough mode. The actual crash is then triggered by concurrent writes to a cached block during invalidation. This can be done by local I/O, not by the network.

Namespaces or containers may matter only if a workload is given access to the affected block device or delegated device-mapper/storage control. That supports a paranoid PR:L style interpretation, but not a strong unprivileged default exposure.

The affected mode is configuration-specific and not a broad default kernel attack surface.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like kernel DoS, not an Important-class issue. Theoretical impact is limited to availability because the patch only prevents dereferencing a NULL `mg->cell`. There is no evidence of attacker-controlled memory corruption, stale lifetime reuse, information disclosure, or privilege escalation.

The paranoid score remains low because even under delegated block-device access, the primitive is still a NULL dereference with a specific dm-cache passthrough configuration.

## 5. One-sentence report phrase

A NULL pointer dereference in dm-cache passthrough invalidation can be triggered by concurrent writes to the same cached block, causing a local kernel crash DoS under a specific device-mapper cache configuration.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for urgent triage unless the target environment delegates writable access to dm-cache devices to untrusted users. Even then, the likely impact remains local DoS only.

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

Patch: dm cache: fix null-deref with concurrent writes in passthrough mode [ Upstream
Commit: 01264a6a3a3ad7ac1d73443299cd5a9568002454
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=01264a6a3a3ad7ac1d73443299cd5a9568002454

Changed files:
  drivers/md/dm-cache-target.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=01264a6a3a3ad7ac1d73443299cd5a9568002454

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

The original Linux kernel CVE announcement for CVE-2026-53064 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53064

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: 0
  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).