[CVE-2026-89709][MODERATE 7.0] lockd, nfsd: RCU-protect nlmsvc_ops dispatch

[CVE-2026-89709][MODERATE 7.0] lockd, nfsd: RCU-protect nlmsvc_ops dispatch

[AL-KERNEL]

CVE: CVE-2026-89709
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: lockd, nfsd: RCU-protect nlmsvc_ops dispatch
Commit: 3c461a1820088fb5889d73a6522369bde45527a9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3c461a1820088fb5889d73a6522369bde45527a9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89709
Analysis date: Fri, 11 Sep 2026 20:37:36 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89709 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89709

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-2026-89709	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89709 CHECK WITH IMPACT FROM ORIG NN LOW	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:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.1';DESCR 'A race in lockd and nfsd callback dispatch can leave nlmsvc_ops pointing to nfsd data and callback functions after the nfsd module is unloaded. A remote NLM client may exercise the affected dispatch paths while a local administrator unloads nfsd, resulting in a NULL pointer dereference or a use after free of unloaded module data or module text. For the CVSS the PR:N is used for the paranoid score because the remote client does not need local code execution or an account on the target. Reliable triggering still requires the high complexity race with concurrent nfsd module unload. The base impact is denial of service. The stale callback and module text use after free provide a plausible worst case path to confidentiality integrity and availability impact and require manual review. Exposure requires lockd and NLM RPC to be reachable and nfsd to be unloadable as a module. These services are commonly limited to trusted storage networks but may be reachable by internal network clients.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)  SKIP CVE-2026-89709 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	LOCK DISK INIT LEAK UAF LINUS  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4	-	-	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 4
* Paranoid score: 4
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 Real UAF or lifetime violation. `nlmsvc_ops` can remain stale while referencing `nfsd_nlm_ops` in nfsd module rodata and callback addresses in nfsd module text after module removal.
* +1 Reliable kernel crash or strong DoS. A stale NULL callback table access can fault. A stale callback into unloaded module text can also fault when the function is invoked.
* +2 Remote reachable dispatch surface. NLM RPC requests can reach the lockd dispatch paths that use `nlmsvc_ops` when lockd is network reachable.
* -1 Narrow concurrent lifetime race. The vulnerable access must overlap with `nfsd` module shutdown and unloading. The remote actor can exercise dispatch, but the supplied evidence does not show that the remote actor can independently trigger the unload operation.

Non-awarded signals:

* Controlled reclaim or replacement of unloaded module rodata or module text is not demonstrated.
* Arbitrary kernel write, directed write, information disclosure, and credential manipulation are not demonstrated.
* Structured stale object exploitation leverage is not awarded. The callback table contains function pointers, but the patch does not show attacker control of the stale table contents, module-memory reuse, or callback target replacement.
* Weak LPE concern is not separately awarded. A module-text UAF alone does not establish a usable privilege-escalation primitive.
* No concrete repeated release, `put`, or refcount mutation through the same dangling reference is shown.
* No additional Availability point is awarded because the same stale callback fault is already counted as the crash or DoS consequence.
* No host-admin penalty is applied. Module unloading requires privileged control, but the supplied evidence does not establish that the attacker must themselves possess that privilege rather than race with an independent administrator action.

3. Reachability analysis

A remote NLM client can reach lockd RPC dispatch paths if lockd is enabled and exposed over the network. The vulnerable stale pointer is used in `nlm_do_fopen` and file-release handling, where lockd invokes callbacks supplied by nfsd.

The complete trigger is compound. An external client can generate NLM requests, while a separate local privileged actor or lifecycle event must unload the modular `nfsd` implementation concurrently. `rmmod nfsd` normally requires host-level module-management privilege, but the supplied patch does not prove that the attacker must control that operation. Therefore `HostAdminRequired=UNKNOWN`.

There is no evidence that a user namespace or network namespace alone can create the complete condition. Namespace-scoped reachability is unresolved because the relevant module unload operation is host-global rather than namespace-local.

The timing condition is meaningful. A stale reader must obtain or retain `nlmsvc_ops` before `nfsd_lockd_shutdown` clears it and waits for readers, while the old module code and callback table are being unloaded.

4. Primitive and severity interpretation

The exact primitive is a real RCU and module-lifetime UAF. `nlmsvc_ops` points to a callback table stored in nfsd module rodata, and its `fopen` and `fclose` members point into nfsd module text. Before the fix, lockd could dereference the pointer and call those callbacks without RCU lifetime protection or a module reference.

This is an active structured callback-table UAF, not fixed stale DMA storage. However, the demonstrated stale use is an immutable callback-table dereference followed by an indirect call into unloaded module code. The supplied evidence establishes a NULL dereference or execution attempt through stale unloaded module text, which supports kernel crash or DoS.

The patch does not establish attacker-controlled replacement of the callback table, controlled reuse of unloaded module memory, callback-target corruption, arbitrary read or write, or a practical LPE chain. Therefore this remains `CLASS_B`, not `CLASS_A`.

`ImportantCandidate=NO` is appropriate on the supplied evidence because the demonstrated outcome is crash-oriented and meaningful post-free reuse leverage is not established. `AutoDowngradeAllowed=YES` is appropriate for automated deprioritization only after confirming that nfsd is modular and unloadable in the affected deployment, lockd is exposed to untrusted NLM clients, and no downstream evidence demonstrates controlled module-memory reuse.

5. One-sentence report phrase

A race between lockd NLM callback dispatch and nfsd module unload can dereference stale nfsd callback data or invoke unloaded module text, causing a kernel crash when a concurrent NLM request reaches the affected path.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether nfsd is built as an unloadable module, whether lockd and NLM RPC are reachable by untrusted clients, and whether the deployment permits nfsd unload while active lockd requests are processed.

7. Call-site confidence

Call-site confidence: high

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

Patch: lockd, nfsd: RCU-protect nlmsvc_ops dispatch
Commit: 3c461a1820088fb5889d73a6522369bde45527a9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3c461a1820088fb5889d73a6522369bde45527a9

Commit description:

nlmsvc_ops is published by nfsd_lockd_init() and cleared by
nfsd_lockd_shutdown() with plain stores, while lockd dereferences
it unguarded from dispatch sites in fs/lockd/svcsubs.c. The pointer
targets nfsd's .rodata and the fopen/fclose callbacks live in nfsd's
.text, so a stale load after rmmod nfsd results in either a NULL
deref or a module-text use-after-free.

Declare nlmsvc_ops as __rcu, publish via rcu_assign_pointer(), clear
via RCU_INIT_POINTER() + synchronize_rcu(). Add a struct module
*owner field to nlmsvc_binding and pin the module across indirect
calls with try_module_get/module_put. When the binding is torn down,
fall back to fput() to avoid leaking struct file references.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260611-nfsd-testing-v2-16-5b90e276f2d9@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/lockd/svcsubs.c
  fs/lockd/svc.c
  fs/lockd/svc4proc.c
  fs/lockd/svcproc.c
  fs/nfsd/lockd.c
  include/linux/lockd/bind.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=3c461a1820088fb5889d73a6522369bde45527a9

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

The original Linux kernel CVE announcement for CVE-2026-89709 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89709

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:N/UI:N/S:U/C:N/I:N/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: unknown
  Paranoid ActionableScore: 4

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).