[CVE-2026-64157][MODERATE 7.0] netfs: Fix partial invalidation of streaming-write folio [ Upstream

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

CVE: CVE-2026-64157
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfs: Fix partial invalidation of streaming-write folio [ Upstream
Commit: f6b2569ae29b666fd15ff2848684c445ba442a39
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f6b2569ae29b666fd15ff2848684c445ba442a39
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64157
Analysis date: Sun, 19 Jul 2026 12:45:33 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
A netfs dirty-range accounting bug in `netfs_invalidate_folio()` can mis-track the remaining dirty bytes after partial folio invalidation, potentially causing incorrect writeback and file data corruption on netfs-backed filesystems.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64157 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64157

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: 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
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CVE-2026-64157	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:N/I:H/A:L';CWE-682;CWE-754;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '5.3';DESCR 'netfs_invalidate_folio() can incorrectly track the dirty range of a streaming write folio when a partial invalidation overlaps the front of the dirty data. The function trims dirty_len but used the start of the invalidation range as dirty_offset instead of the end of that range, so later writeback may operate on stale or incorrectly described file data. For the CVSS the PR:L is used because a local user or local process with access to files on a netfs backed mount is needed to create the affected folio and invalidation pattern. The issue is not directly network reachable as an attack interface, although the corrupted data may be stored on a remote network filesystem backend. Impact is primarily integrity loss through possible file data corruption, with limited availability impact in the paranoid case if corruption affects important shared storage state.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-64157 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: cce6bfa6ca0e30af9927b0074c97fe6a92f28092 YES  NO NO unknown 	MAYBE	REMOTE DISK SIMPLEFIX LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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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 user or local process with access to a netfs-backed mount may be able to create writes and invalidation patterns affecting streaming-write folios.
* Memory layout invariant restoration: +1. The patch restores consistency between `dirty_len`, `dirty_offset`, `offset`, and `iend` in filesystem folio dirty-range tracking.
* Integrity impact plausible: +1. Incorrect dirty-range tracking can cause later writeback to operate on stale or incorrectly described file data.
* Important filesystem/storage path: +1. This is in netfs folio invalidation and writeback-related state, affecting filesystem data integrity.
* Hard or special trigger conditions: -1. The bug requires a partial invalidation overlapping the front of a dirty but not uptodate streaming-write folio with `netfs_folio` dirty-range metadata.

Paranoid additional interpretation:

* Page-cache or file-backed data corruption concern: +2. The affected object is a folio with dirty cached file data, and the bug can misdescribe what range should be written back. This is not Dirty-Pipe-equivalent, but it is still page-cache/writeback-adjacent data corruption.
* No memory-corruption or LPE bonus. The patch does not show UAF, OOB write, refcount misuse, type confusion, arbitrary write, callback control, or attacker-controlled reclaim.

## 3. Reachability analysis

The likely trigger is local file activity on a netfs-backed filesystem, not a direct network packet path. A remote server may store the corrupted data, but the attacker interface is local filesystem access rather than network reachability.

Namespaces and containers may matter if an untrusted workload has access to a mounted netfs filesystem. This does not require full host root in the abstract, but it does require the relevant mount and file access pattern. The path is configuration-dependent because it requires netfs streaming-write behavior and a specific partial invalidation case.

Call-site confidence: medium. The patch provides the affected function and dirty-range logic, but not all writeback and invalidation call sites.

## 4. Severity interpretation

This behaves more like an actionable Moderate filesystem data-integrity issue than an Important memory-corruption vulnerability. The realistic impact is file data corruption or incorrect writeback state. The theoretical risk is elevated because page-cache and writeback bugs can affect shared storage integrity, but the patch does not support privilege escalation or kernel memory corruption.

## 5. One-sentence report phrase

A netfs dirty-range accounting bug in `netfs_invalidate_folio()` can mis-track the remaining dirty bytes after partial folio invalidation, potentially causing incorrect writeback and file data corruption on netfs-backed filesystems.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is filesystem/page-cache-adjacent data corruption with a defensible paranoid score of 5, even though there is no demonstrated memory-corruption or privilege-escalation primitive.

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

Patch: netfs: Fix partial invalidation of streaming-write folio [ Upstream
Commit: f6b2569ae29b666fd15ff2848684c445ba442a39
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f6b2569ae29b666fd15ff2848684c445ba442a39

Changed files:
  fs/netfs/misc.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=f6b2569ae29b666fd15ff2848684c445ba442a39

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

The original Linux kernel CVE announcement for CVE-2026-64157 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64157

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:N
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L
  The Best / paranoid CVSS score: 5.3

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).