[CVE-2026-74542][MODERATE REGULAR] netfs: Fix folio_queue ENOMEM in writeback by adding a mempool [ Upstream

[CVE-2026-74542][MODERATE REGULAR] netfs: Fix folio_queue ENOMEM in writeback by adding a mempool [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74542
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfs: Fix folio_queue ENOMEM in writeback by adding a mempool [ Upstream
Commit: 3f6d7f8a5416d852648d15a05e895f1195ee8a85
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3f6d7f8a5416d852648d15a05e895f1195ee8a85
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74542
Analysis date: Sat, 15 Aug 2026 11:40:42 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
netfs writeback could fail folio_queue allocation under memory pressure, causing WARN or writeback stall behavior, but the patch indicates a DoS-only allocation robustness issue without supported memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-74542 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74542

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 REGULAR
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-2026-74542	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: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 'netfs writeback could hit folio_queue allocation failure under memory pressure because the rolling buffer allocation path did not reliably use a mempool for writeback requests. This can trigger a WARN in netfs_writepages and may cause writeback failure or stalled reclaim behavior on filesystems using netfs. For the CVSS the PR:L value is used because a local user or local process with write access to an affected mounted filesystem may be able to trigger the condition by causing writeback under memory pressure. The issue is not directly network reachable and is not caused by packet input. Impact is denial of service only. No concrete UAF, OOB access, information leak, or arbitrary write primitive is indicated by the code changes.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 3)  SKIP CVE-2026-74542 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: cd0277ed0c188dd40e7744e89299af7b78831ca4 YES  NO NO unknown 	MAYBE	REMOTE WRITE OOB DANGER DISK INIT NOMEMCHK HARDWARE LINUS SYZBOT  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  A local user or process with write access to a filesystem using netfs may be able to create writeback activity under memory pressure.

* Important filesystem/storage path: +1
  The bug is in netfs writeback and rolling buffer allocation, which is a filesystem writeback path.

Paranoid additional signal:

* Availability impact realistic: +1
  In a worse practical case, repeated ENOMEM in writeback during reclaim could stall writeback or reclaim behavior and cause broader availability degradation.

Negative or not awarded:

* No memory corruption signal. The patch does not show UAF, OOB write, double free, stale pointer reuse, arbitrary write, or page-cache ownership corruption.
* No privilege escalation signal. There is no supported LPE primitive.
* No confidentiality or integrity signal. The failure mode is ENOMEM, WARN, and writeback failure or stall.
* No remote reachability. This is not packet-triggered despite netfs being used by network filesystems.
* Hard or special condition: -1 could be argued for the conservative path because memory pressure and writeback timing are needed, but I did not subtract it in the lower score to avoid undercounting the writeback relevance. If applied strictly, the lower score would be 1.

## 3. Reachability analysis

A local user can plausibly trigger the affected path by writing data to a mounted filesystem backed by netfs and causing writeback under memory pressure. This does not require CAP_SYS_ADMIN if the filesystem is already mounted and writable by that user. Containers may matter only if the container can write to an affected netfs-backed mount and influence memory pressure, but the bug does not itself indicate a namespace escape.

The path is not directly network reachable. Remote storage servers may influence I/O timing, but the failing allocation is local writeback memory handling, not remote protocol parsing. The affected subsystem is not a universal default path, but netfs writeback is security-relevant enough not to treat as an obscure driver-only issue.

Call-site confidence: high, because the patch includes the relevant callers in buffered read, write issue, request allocation, subrequest allocation, and rolling buffer helpers.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like availability issue, not an Important-class vulnerability. The realistic impact is WARN, failed writeback, or possible reclaim/writeback stall under memory pressure. The patch is a robustness fix that introduces a folio_queue mempool and propagates GFP flags so writeback allocations do not fail in reclaim-sensitive contexts.

Theoretical memory corruption potential is not supported by the patch. There is no demonstrated stale pointer, attacker-controlled reclaim, overwrite, refcount misuse, or shared page ownership violation. The paranoid score is only raised for stronger availability impact, not for confidentiality, integrity, or privilege escalation.

## 5. One-sentence report phrase

netfs writeback could fail folio_queue allocation under memory pressure, causing WARN or writeback stall behavior, but the patch indicates a DoS-only allocation robustness issue without supported memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be handled as an auto-close or deferred low-priority Moderate unless product-specific evidence shows reliable system-wide stalls on common netfs deployments.

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

Patch: netfs: Fix folio_queue ENOMEM in writeback by adding a mempool [ Upstream
Commit: 3f6d7f8a5416d852648d15a05e895f1195ee8a85
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3f6d7f8a5416d852648d15a05e895f1195ee8a85

Changed files:
  fs/netfs/write_issue.c
  fs/netfs/buffered_read.c
  fs/netfs/internal.h
  fs/netfs/main.c
  fs/netfs/objects.c
  fs/netfs/read_pgpriv2.c
  fs/netfs/rolling_buffer.c
  include/linux/netfs.h
  include/linux/rolling_buffer.h

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=3f6d7f8a5416d852648d15a05e895f1195ee8a85

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

The original Linux kernel CVE announcement for CVE-2026-74542 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74542

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: 2
  Paranoid ActionableScore: 3

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 REGULAR

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).