[CVE-2026-89485][MODERATE 7.0] lockd: pin next file across nlm_inspect_file lock-drop

[CVE-2026-89485][MODERATE 7.0] lockd: pin next file across nlm_inspect_file lock-drop

[AL-KERNEL]

CVE: CVE-2026-89485
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: lockd: pin next file across nlm_inspect_file lock-drop
Commit: c24bdb7df2f34bdc38ca8a73796f5acb40f1830c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c24bdb7df2f34bdc38ca8a73796f5acb40f1830c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89485
Analysis date: Sat, 12 Sep 2026 05:08:22 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89485 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89485

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-2026-89485	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89485 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'A race in lockd nlm_traverse_files can dereference a freed nlm_file object because the iterator pins the current file but not the saved next file while dropping nlm_file_mutex around nlm_inspect_file. A concurrent nlm_release_file can unlink and kfree that next object during the unlock window, leaving the iterator to access freed slab memory on the next loop step. For the CVSS the PR:N is used in the paranoid score because an exposed NFS lockd service may be reachable by a remote client without a local account on the target, although reliable triggering still requires NFS/NLM access and a race window. The issue is network reachable when lockd is exposed to untrusted or semi trusted NFS clients. Impact is at least denial of service via kernel crash, and in the worst case may allow confidentiality or integrity impact due to UAF based memory corruption. NFS and lockd are usually deployed inside trusted storage or data center networks rather than the public Internet, but exposure to untrusted clients should be treated as high risk.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 6)	YES	LOCK DEADLOCK DISK UAF KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	NO	NO	checked

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

ActionableScore=7
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5. No floor or cap applied.
* Raw paranoid score: 7
* Paranoid score: 7. No floor or cap applied.
* Final recommended bucket: **Strong Important candidate**::

2. Signal breakdown

Conservative signals:

* +2 Real UAF / lifetime violation: `nlm_traverse_files()` saves `next` without pinning it, drops `nlm_file_mutex`, and a concurrent `nlm_release_file()` can unlink and `kfree()` that next `struct nlm_file`.
* +2 Remote reachable / network-facing service: lockd/NLM is an NFS network service, and remote NFS/NLM clients can influence lock/file lifetime when the service is exposed.
* +1 Reliable kernel crash / strong DoS: the commit explicitly describes dereferencing freed slab memory on the next iterator step.

Paranoid additional signals:

* +1 Attacker-influenced active-object lifetime manipulation: an NFS/NLM client can plausibly create and release lockd file state repeatedly, making the lifetime transition more attacker-influenced than a one-shot teardown.
* +1 Structured stale-object exploitation leverage: the stale object is an active `struct nlm_file` in a hash/list traversal, and later iteration can consume list/refcount state rather than only touching fixed stale storage.

Non-awarded signals:

* +0 Strong LPE leverage: controlled reclaim, object replacement, arbitrary write, callback control, or credential manipulation is not demonstrated.
* +0 Confidentiality and Integrity: not awarded merely because UAF exists.
* +0 Extra Availability: not awarded because the same crash is already counted.
* +0 Hard race penalty: not applied because the patch establishes a race window, but not a rare one-shot or externally uncontrollable timing condition.
* +0 Concrete repeated release/refcount signal: withheld. A concurrent release can free `next`, and the stale iterator may later touch structured fields, but the patch does not clearly establish a deterministic second put/release on the exact same reference after an earlier release by the same control flow.
* FLOOR 5: not needed for conservative score, which already reaches 5.

3. Reachability analysis

The vulnerable code is in lockd/NLM file traversal. A remote NFS/NLM client can plausibly create and remove lock state and cause `nlm_release_file()` activity if the lockd service is reachable. The traversal side may depend on server-side lockd operations, failover, or cleanup paths, so the exact complete trigger chain is not fully visible from the supplied diff. However, host administrator privilege is not positively required for the attacker role when the service is exposed to remote NFS/NLM clients. No namespace-scoped privilege conclusion is established. Prior server configuration such as exporting NFS and running lockd is a deployment prerequisite, but not a privilege requirement for a remote client already able to interact with the service. Race repeatability appears plausible under concurrent lock creation/release and traversal activity, but exact exploit reliability needs manual review.

4. Primitive and severity interpretation

The exact primitive is a race-based use-after-free of `struct nlm_file`. This is an active structured object, not fixed stale storage. The demonstrated stale use is an iterator dereference of a freed object during hash/list traversal, with possible subsequent use of list and refcount-related state if execution continues. This is CLASS_B because a concrete kernel lifetime violation is established, but controlled reclaim or a directed corruption primitive is not demonstrated.

This is not merely an ordinary stale cleanup dereference. The stale object participates in active lockd table traversal. However, the supplied patch does not conclusively establish a concrete repeated release/refcount mutation on the exact same dangling reference, so the dedicated repeated-release rule is not awarded.

Demonstrated consequence is kernel crash or host DoS. Speculative consequence is broader memory corruption if stale `nlm_file` storage is reused and later interpreted as valid structured lockd state. ImportantCandidate is YES because this is a network-facing active-object UAF with unresolved exploitation leverage. AutoDowngradeAllowed is NO because automatically closing it as ordinary Moderate would discard a concrete kernel UAF in a remotely reachable subsystem.

5. One-sentence report phrase

A race in lockd `nlm_traverse_files()` can leave an unpinned `nlm_file` next pointer dangling across a mutex drop, allowing a remote NFS/NLM client in exposed deployments to trigger a use-after-free and kernel crash, with broader memory-corruption impact requiring manual review.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a concrete network-facing active-object UAF in lockd/NFS, with at least DoS demonstrated and unresolved post-free structured-object leverage.

7. Call-site confidence

Call-site confidence: medium

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

Patch: lockd: pin next file across nlm_inspect_file lock-drop
Commit: c24bdb7df2f34bdc38ca8a73796f5acb40f1830c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c24bdb7df2f34bdc38ca8a73796f5acb40f1830c

Commit description:

nlm_traverse_files() pins the current file with f_count++ across
a mutex_unlock for nlm_inspect_file(), but nothing pins the saved
next pointer.  A concurrent nlm_release_file() can kfree the next
file during the unlock window, and the iterator dereferences freed
memory on the next loop step.

Pin both current and next before the lock-drop.  Advance by
swapping the pinned cursors at the end of each iteration so next
is always held alive across the unlock.

Always call nlm_file_release() after dropping the iteration pin,
regardless of whether the file matched the predicate.  Use
nlm_file_inuse(), which does a live walk of the inode lock list,
rather than the cached f_locks field, so skipped files that never
ran nlm_inspect_file() are evaluated correctly.

Because every file in a hash bucket is now pinned and released,
files skipped by the is_failover_file predicate that have no
locks, blocks, shares, or external references are deleted during
traversal.  The old code never evaluated skipped files for
cleanup.  The new behavior is intentional: such files are stale
and should not persist in the table.

Fixes: 01df9c5 ("LOCKD: Fix a deadlock in nlm_traverse_files()")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Link: https://patch.msgid.link/20260524115527.1734251-1-michael.bommarito@gmail.com
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/lockd/svcsubs.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=c24bdb7df2f34bdc38ca8a73796f5acb40f1830c

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

The original Linux kernel CVE announcement for CVE-2026-89485 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89485

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:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.1

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: 5
  Paranoid ActionableScore: 7

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: YES
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).