[CVE-2026-64062][LOW] netfs: Fix potential deadlock in write-through mode [ Upstream

[CVE-2026-64062][LOW] netfs: Fix potential deadlock in write-through mode [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64062
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: netfs: Fix potential deadlock in write-through mode [ Upstream
Commit: 1468f39243ccb155b6d97f9a9932f610d1205d75
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1468f39243ccb155b6d97f9a9932f610d1205d75
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64062
Analysis date: Sun, 19 Jul 2026 21:28:35 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-64062 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64062

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-2026-64062	LOW	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-833;CWE-667;*CWE-664;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 potential deadlock exists in the netfs write-through path because a folio can be handled with the wrong lock and writeback ordering during partial writes. If the folio is marked for writeback before it is fully ready, mmap reads or mmap writes can wait against that state and the write-through operation can stall. For the CVSS the PR:L is used because a local user or process with write access to a file on an affected netfs mount can potentially exercise the write path, while administrative privileges are not necessarily required after the mount already exists. The issue is not directly network reachable because it is triggered through local filesystem write operations rather than by remote packet input. Impact is denial of service through blocked writeback or hung filesystem operations, with no evidence of memory corruption or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)  SKIP CVE-2026-64062 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 288ace2f57c9d06dd2e42bd80d03747d879a4068 YES  NO NO unknown 	MAYBE	REMOTE READ DEADLOCK DISK INIT 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

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

2. Signal breakdown
* Local unprivileged trigger: +1. A local user or process with write access to an affected netfs-backed mount may exercise the write-through path after the mount exists.
* Important filesystem/storage path: +1. The bug is in netfs folio write-through and writeback state handling.
* Availability impact realistic: +1. The described failure mode is a deadlock or hung filesystem operation involving premature writeback state and mmap reads or writes.
* Hard or configuration-dependent trigger: -1. Triggering depends on write-through mode, partial folio handling, and mmap/writeback interaction.
* No memory corruption signal: +0. The patch fixes lock, dirty, writeback, and folio reference ordering, but does not show UAF, OOB write, double free, type confusion, or page-cache ownership corruption.
* No privilege escalation signal: +0. There is no concrete primitive for LPE beyond denial of service.

3. Reachability analysis
A local workload with write access to files on an affected netfs mount is the realistic trigger. Administrative privileges may be needed to create the mount, but not necessarily to trigger the faulty write path once the mount is available. Namespaces or containers only matter if they can access such a mounted filesystem. The path is not directly network-triggerable by packets alone. Realistic exploitation conditions require a suitable netfs write-through workload and timing with mmap reads or writes.

4. Severity interpretation
This behaves like an ordinary Moderate or Low-like availability bug, not an Important-class vulnerability. Theoretical impact is a filesystem operation deadlock or stall. There is no evidence of memory corruption, confidentiality impact, integrity impact, or privilege escalation. Call-site confidence: high, because the relevant write-through and end-write-through call paths are present in the patch.

5. One-sentence report phrase
A netfs write-through folio state ordering bug can cause a local denial of service by deadlocking mmap reads or writes against premature writeback handling, but the patch does not indicate memory corruption or privilege escalation.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. The issue is a local availability-only deadlock with no demonstrated memory corruption, security-boundary bypass, or LPE primitive.

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

Patch: netfs: Fix potential deadlock in write-through mode [ Upstream
Commit: 1468f39243ccb155b6d97f9a9932f610d1205d75
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1468f39243ccb155b6d97f9a9932f610d1205d75

Changed files:
  fs/netfs/write_issue.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=1468f39243ccb155b6d97f9a9932f610d1205d75

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

The original Linux kernel CVE announcement for CVE-2026-64062 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64062

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).