[CVE-2026-72472][MODERATE 7.0] nfs: use nfsi->rwsem to protect traversal of the file lock list [ Upstream

[CVE-2026-72472][MODERATE 7.0] nfs: use nfsi->rwsem to protect traversal of the file lock list [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72472
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: nfs: use nfsi->rwsem to protect traversal of the file lock list [ Upstream
Commit: 1cda95bf2e9c0e6b63545b7565fe4a1e474322f4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1cda95bf2e9c0e6b63545b7565fe4a1e474322f4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72472
Analysis date: Sun, 16 Aug 2026 01:51:08 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in NFSv4 file lock traversal can leave a stale file_lock object reachable during delegation recall or lock recovery, creating a local UAF and kernel crash risk with possible but unproven privilege escalation potential.

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

The original Linux kernel CVE announcement for CVE-2026-72472 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72472

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-72472	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:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in NFSv4 file lock handling can occur because file lock list traversal was not consistently protected while operations such as lock recovery or delegation recall may sleep or take a long time. If another path removes or updates a file lock while the traversal is in progress, the client can continue using a stale file_lock object and hit a use-after-free condition. For the CVSS the PR:L is used because a local user process can interact with files and byte range locks on an existing NFS mount, while reliable triggering still depends on NFSv4 recovery or delegation recall timing. The issue is not directly network reachable as an unauthenticated remote packet attack against the kernel. Impact is at least a local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	DEADLOCK DANGER DISK UAF NETWORK  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local user with access to an existing NFSv4 mount can exercise byte range locks and unlocks.
* Memory corruption, weak or indirect corruption candidate: +1. The commit explicitly discusses avoiding UAF while traversing the file lock list, but does not show controlled reclaim, object replacement, callback control, or arbitrary write.
* Real lifetime corruption: +1. The bug is a lifetime race around file_lock objects and lock list traversal.
* Reliable kernel crash or strong DoS concern: +1. A stale file_lock object can plausibly crash the kernel during lock reclaim or delegation recall paths.
* Important filesystem/storage path: +1. NFSv4 locking, delegation recall, and recovery are important filesystem client paths.
* Hard or unreliable race / special timing required: -1. Triggering depends on timing between lock list traversal, lock or unlock operations, reclaim, and delegation recall.

Paranoid additional signal:

* Broad enterprise exposure: +1. NFSv4 is commonly deployed in enterprise and storage environments, even though the vulnerable path requires specific lock recovery or delegation conditions.

## 3. Reachability analysis

The bug is locally triggerable from an NFS client by a user process that can access files on an already mounted NFSv4 filesystem and manipulate file locks. Mounting NFS itself is normally privileged, but exploiting behavior on an existing shared mount may not require admin privileges, so PR:L is the practical assumption. Containers or restricted service accounts may matter if they can access the mounted NFS tree and create byte range locks, but this is not a direct remote packet parsing issue against the kernel. Realistic exploitation requires NFSv4 lock recovery or delegation recall timing, so the race is not a simple always-on local primitive.

## 4. Severity interpretation

This is stronger than an ordinary Moderate correctness bug because the patch and commit text explicitly identify a UAF risk in kernel file lock list traversal. It is not enough to classify as Important with high confidence because the patch does not demonstrate attacker-controlled reclaim, stale object replacement, function pointer control, write-after-free, or a concrete LPE primitive. The conservative interpretation is borderline manual-review territory. The paranoid interpretation is Actionable Moderate because local user influence over NFS locks plus a real kernel lifetime bug can historically be underestimated.

## 5. One-sentence report phrase

A race in NFSv4 file lock traversal can leave a stale file_lock object reachable during delegation recall or lock recovery, creating a local UAF and kernel crash risk with possible but unproven privilege escalation potential.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the commit explicitly references UAF avoidance in a kernel filesystem locking path, and local users may be able to shape file_lock objects on existing NFS mounts. The lack of a demonstrated reclaim or overwrite primitive keeps the main score below Strong Important, but the lifetime-corruption class should not be auto-closed.

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

Patch: nfs: use nfsi->rwsem to protect traversal of the file lock list [ Upstream
Commit: 1cda95bf2e9c0e6b63545b7565fe4a1e474322f4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1cda95bf2e9c0e6b63545b7565fe4a1e474322f4

Changed files:
  fs/nfs/delegation.c
  fs/nfs/nfs4proc.c
  include/linux/nfs_xdr.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=1cda95bf2e9c0e6b63545b7565fe4a1e474322f4

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

The original Linux kernel CVE announcement for CVE-2026-72472 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72472

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 4
  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).