[CVE-2026-64058][MODERATE 7.0] netfs: Fix netfs_read_folio() to wait on writeback [ Upstream

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

CVE: CVE-2026-64058
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfs: Fix netfs_read_folio() to wait on writeback [ Upstream
Commit: f17b9121bb99f88188ec9be2db5da1d561f4c01b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f17b9121bb99f88188ec9be2db5da1d561f4c01b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64058
Analysis date: Sun, 19 Jul 2026 16:14:30 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in netfs_read_folio() can allow the read path to trust dirty state and folio private data before concurrent writeback cleanup has fully completed, creating a local filesystem page-cache integrity risk with possible I/O disruption.

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

The original Linux kernel CVE announcement for CVE-2026-64058 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64058

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-64058	MODERATE	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:L/I:H/A:L';CWE-362;CWE-667;CWE-404;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.8';DESCR 'netfs_read_folio() could inspect dirty state and folio private data while writeback was still in progress. The writeback collector may clean folio private before the writeback flag is cleared, so a concurrent read path can make decisions using inconsistent folio state. For the CVSS the PR:L is used because a local process with access to files on an affected netfs backed mount is needed to trigger the read/writeback race. The issue is not directly network reachable even though the backing filesystem may use network storage. Impact is primarily local data integrity loss or I/O disruption. For the paranoid score, choose the highest still defensible interpretation supported by the bug class and patch context, with preference for manual review sensitivity over autoclosed false negatives.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-64058 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: ee4cdf7ba857a894ad1650d6ab77669cbbfa329e YES  NO NO unknown 	MAYBE	REMOTE DISK SIMPLEFIX LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  A local process with access to files on an affected netfs backed mount can plausibly exercise reads while writeback is in progress.

* Real lifetime corruption: +1
  The commit explicitly says folio private data may be cleaned up by the collector before the writeback flag is cleared. This is a real lifetime ordering issue around folio private state.

* Integrity impact plausible: +1
  The read path may make decisions from inconsistent dirty state and folio private state, which can plausibly affect file/page-cache data correctness.

* Important filesystem/storage path: +1
  The bug is in netfs buffered read/writeback interaction, which is a filesystem page-cache path.

* Hard or unreliable race: -1
  Triggering requires a timing window between read_folio and concurrent writeback completion or collector cleanup.

Paranoid additional signals:

* Weak or indirect corruption candidate: +1
  The stale or prematurely cleaned folio private state is not a demonstrated UAF reclaim or write primitive, but it is a plausible indirect corruption sink in a filesystem folio state machine.

* Confidentiality impact plausible: +1
  In the paranoid interpretation, inconsistent page-cache or folio-private state could expose stale or unintended file data, but this is not proven by the patch.

Not awarded:

* No remote reachable score. The affected backing filesystem may be network based, but the vulnerable operation is local page-cache read/writeback behavior.
* No strong LPE score. The patch does not show attacker-controlled reclaim, object replacement, arbitrary write, callback control, or type confusion.
* No Dirty-Pipe-like bonus. There is no clear externally owned page or COW bypass write primitive shown.
* No strong memory corruption score. The primitive is a race in folio-private lifetime/state handling, not a demonstrated UAF exploitation primitive.

## 3. Reachability analysis

The likely trigger is a local process accessing files on a filesystem using netfs buffered reads while writeback is active on the same folio. No special network packet or remote protocol message directly reaches this path. Namespaces or containers may matter only if the affected netfs mount is exposed inside them, because an unprivileged container workload could still generate the local file I/O pattern. The path is not exotic kernel debugging code, but practical triggering depends on an affected netfs-backed filesystem and a read/writeback race, so exploitation is timing dependent.

Call-site confidence: medium. The changed function and immediate condition are visible, and the commit describes the folio-private lifetime issue, but broader caller behavior and concrete failure traces are not included.

## 4. Severity interpretation

This behaves more like an actionable Moderate than an ordinary low-risk cleanup. The realistic impact is local filesystem data integrity disruption or I/O correctness failure under a race. The paranoid concern is that stale folio-private state in a page-cache/writeback path can sometimes become more security relevant than a simple crash, but the patch does not demonstrate a practical privilege escalation primitive. Therefore the main result should not be treated as Important-class without further evidence, but it should also not be auto-closed as a routine low Moderate.

## 5. One-sentence report phrase

A race in netfs_read_folio() can allow the read path to trust dirty state and folio private data before concurrent writeback cleanup has fully completed, creating a local filesystem page-cache integrity risk with possible I/O disruption.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because this is a filesystem folio-private lifetime race in a page-cache/writeback path, with plausible integrity impact and a defensible paranoid ActionableScore of 5 even though a concrete LPE primitive is not shown.

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

Patch: netfs: Fix netfs_read_folio() to wait on writeback [ Upstream
Commit: f17b9121bb99f88188ec9be2db5da1d561f4c01b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f17b9121bb99f88188ec9be2db5da1d561f4c01b

Changed files:
  fs/netfs/buffered_read.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=f17b9121bb99f88188ec9be2db5da1d561f4c01b

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

The original Linux kernel CVE announcement for CVE-2026-64058 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64058

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:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:L
  The Best / paranoid CVSS score: 5.8

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: 3
  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).