[CVE-2026-53063][LOW] dm cache: fix write hang in passthrough mode [ Upstream

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

CVE: CVE-2026-53063
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: dm cache: fix write hang in passthrough mode [ Upstream
Commit: 9fa18d0b981776b190ca4632942a7c2174052b78
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9fa18d0b981776b190ca4632942a7c2174052b78
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53063
Analysis date: Fri, 26 Jun 2026 12:24:53 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A dm-cache passthrough mode logic error can drop a remapped write bio after cache invalidation, causing local write I/O hangs and storage availability degradation under specific configuration conditions.

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

The original Linux kernel CVE announcement for CVE-2026-53063 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53063

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-2026-53063	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-703;CWE-755;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A logic error in dm cache passthrough mode can drop a write hit bio after cache invalidation. The affected path prepares the overwrite bio for remapping to the cache origin but does not submit it, which can leave write IO waiting indefinitely. For the CVSS the PR:L is used for the paranoid score because a local user or process with write access to a filesystem or block device backed by an already configured dm cache target may be able to trigger the affected write path, while creating or configuring the dm cache target is normally administrative. The issue is not network reachable and does not show a concrete memory corruption primitive. Impact is denial of service through hung write operations and possible storage stack degradation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) 	MAYBE	DISK INIT ERRORPATH IMPROVEONLY LINUS 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local process with write access to a filesystem or block device backed by an already configured dm-cache target may reach the affected write path.

* Reliable kernel/storage DoS: +1
  The bug can drop an overwrite bio after remapping setup, leaving write I/O hanging.

* Important filesystem/storage path: +1
  dm-cache is in the block/storage stack and write hangs can affect storage availability.

* Rare AND difficult-to-reach subsystem/configuration: -1
  Triggering requires dm-cache in passthrough mode plus cache invalidation and write-hit conditions. This is not a default common path.

No points for memory corruption, lifetime corruption, privilege escalation, network reachability, or security-boundary bypass.

## 3. Reachability analysis

The vulnerable path is local and storage-stack dependent. Creating and configuring the dm-cache target normally requires administrative privileges, but once such a device exists, a less privileged local user may be able to trigger writes through a mounted filesystem or exposed block device. Containers or namespaces do not obviously lower the requirement unless the dm-cache-backed storage is deliberately exposed into the container. The issue is not network reachable by itself.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like availability issue. The patch shows a logic error where an overwrite bio is prepared but not submitted, causing hung writes. There is no evidence of UAF, OOB access, attacker-controlled overwrite, page-cache corruption, privilege escalation, or information disclosure. The realistic impact is DoS through stalled write I/O under specific dm-cache passthrough conditions.

## 5. One-sentence report phrase

A dm-cache passthrough mode logic error can drop a remapped write bio after cache invalidation, causing local write I/O hangs and storage availability degradation under specific configuration conditions.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a configuration-dependent DoS-only storage hang with no supported memory corruption or privilege escalation primitive.

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

Patch: dm cache: fix write hang in passthrough mode [ Upstream
Commit: 9fa18d0b981776b190ca4632942a7c2174052b78
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9fa18d0b981776b190ca4632942a7c2174052b78

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=9fa18d0b981776b190ca4632942a7c2174052b78

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

The original Linux kernel CVE announcement for CVE-2026-53063 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53063

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:N/A:L
  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: unknown
  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).