[CVE-2026-89684][MODERATE 7.0] nfsd: fix cpntf publish race in nfs4_init_cp_state

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

CVE: CVE-2026-89684
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: nfsd: fix cpntf publish race in nfs4_init_cp_state
Commit: 21d6c5957f5ca97d7352e60f55ea412beb9419f5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=21d6c5957f5ca97d7352e60f55ea412beb9419f5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89684
Analysis date: Sat, 12 Sep 2026 02:44:18 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A network reachable NFSD COPY_NOTIFY publication race can expose a partially initialized cpntf state to OFFLOAD_CANCEL, causing a kernel oops and leaving an unresolved active object lifetime violation that requires manual review.

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

The original Linux kernel CVE announcement for CVE-2026-89684 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89684

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-2026-89684	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89684 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:L/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;**CWE-476;Other CVSS 'AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A server side race in NFSD COPY_NOTIFY state publication can make a new cpntf state reachable through the s2s_cp_stateids IDR before its cp_list entry is fully linked. A racing NFSv4.2 client can use the echoed cnr_stateid in OFFLOAD_CANCEL to reach manage_cpntf_state and free the partially published object, which can cause list_del on an uninitialized list_head, a kernel oops, and a server DoS. The same publish before link pattern is a use-after-free candidate because the allocation path may continue after the racing cancel has dropped the last reference and freed the cpntf object. For the CVSS the PR:L is used for the paranoid score because the attacker generally needs access as an NFSv4.2 client able to drive COPY_NOTIFY and OFFLOAD_CANCEL, but does not need local privileges on the server. The issue is network reachable through the NFS server control path and is most relevant on internal storage or data center networks where NFSv4.2 server side copy features are exposed. Impact is at least remote denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to a race based use-after-free candidate.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	YES	LOCK DANGER DISK INIT RACE NETWORK LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	YES	NO	checked

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

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

## 1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 6
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

No floor or cap changed the score.

## 2. Signal breakdown

Conservative signals:

* +2 Remote reachable / directly network-triggerable: the commit states that `so_id` is echoed to the client as `cnr_stateid`, and a racing NFSv4.2 client can drive `OFFLOAD_CANCEL`.
* +2 Real UAF / active lifetime violation: the cpntf object is published in `s2s_cp_stateids` before it is fully linked into `sc_cp_list`; a racing cancel path can reach `_free_cpntf_state_locked()` while the creator still holds and continues using the object.
* +1 Reliable kernel crash / strong DoS: `list_del()` on a zeroed `{NULL,NULL}` `list_head` is explicitly described as oopsing the server.
* +1 Attacker-influenced repeatable lifetime manipulation: the NFSv4.2 client can drive the creation and cancellation sequence repeatedly through protocol operations.
* -1 Hard timing race: the vulnerable condition depends on hitting the narrow window between IDR publication and list insertion.

Paranoid difference:

* The paranoid score withholds the -1 timing penalty because the same remote client can repeatedly drive the COPY_NOTIFY / OFFLOAD_CANCEL lifecycle, making the race operationally testable rather than a one-shot teardown race.

Important non-awarded signals:

* Controlled reclaim not demonstrated.
* Arbitrary kernel read/write not demonstrated.
* Strong LPE leverage +2 not awarded.
* Structured stale-object leverage +1 not separately awarded because the main unresolved issue is already captured as active lifetime violation plus repeatable lifetime manipulation.
* Extra availability point not awarded because the same oops/crash is already counted once.
* Confidentiality and integrity points are not awarded as established consequences. They remain unresolved paranoid concerns, not demonstrated impact.

Repeated-release/refcount checklist:

* First release can end lifetime: yes, `_free_cpntf_state_locked()` uses `refcount_dec_and_test()` and then proceeds toward unlink, IDR removal, and `kfree(cps)`.
* Exact same reference survives: yes, the allocation path still has `cps` / `stid` after publication and before old-code `list_add()`.
* Second lifetime/refcount mutation: not clearly established as a second refcount decrement on the exact same dangling reference.
* +1 Concrete repeated release/refcount: not awarded.
* Paranoid repeated-refcount leverage +1: not awarded.
* FLOOR 5: not needed because raw conservative score is already 5.

## 3. Reachability analysis

The evaluated attacker is a remote NFSv4.2 client with access to the NFSD service and the relevant COPY_NOTIFY / OFFLOAD_CANCEL functionality. The supplied text explicitly says any NFSv4.2 client can drive the racing `OFFLOAD_CANCEL` using the echoed `cnr_stateid`.

Host administrator privileges are not required on the server side. This is not a namespace-scoped local capability issue; it is a network service protocol path. Prior server setup is required in the ordinary sense that NFSD and NFSv4.2 server-side copy functionality must be enabled and reachable, but that is deployment exposure rather than attacker privilege.

The race is real because the object is visible in the IDR before list linkage is complete. The timing window is narrow in the conservative interpretation, but repeated protocol attempts make it credible enough for manual security review.

## 4. Primitive and severity interpretation

The exact primitive is a server-side publication race for `struct nfs4_cpntf_state`. The object becomes reachable through `s2s_cp_stateids` before its `cp_list` is initialized and linked. A racing cancel path can treat the partially initialized object as a valid COPY_NOTIFY state and enter the free path.

This is an active structured object lifetime violation, not fixed stale storage. The demonstrated consequence is a kernel oops from `list_del()` on an uninitialized list head, causing NFSD/server DoS. The stronger unresolved concern is that the same race is a UAF candidate: the cancel/free path can drop the final reference while the construction path still has a raw pointer and would proceed to operate on the object.

PrimitiveClass is CLASS_B. It is stronger than CLASS_C because the bug is not merely an invalid value or passive NULL dereference; it is a remotely reachable active-object lifetime/publication race. It is not CLASS_A because controlled reclaim, object replacement, arbitrary write, callback control, or demonstrated LPE is not established.

ImportantCandidate=YES because this is a network-reachable kernel lifetime race in NFSD with plausible post-lifetime object use beyond a simple validation failure. AutoDowngradeAllowed=NO because automatic closure as ordinary DoS would discard unresolved lifetime-corruption leverage.

Likely operational severity is actionable Moderate at minimum, with Strong Important review warranted if further analysis confirms usable UAF behavior beyond the immediate list corruption/oops.

## 5. One-sentence report phrase

A network reachable NFSD COPY_NOTIFY publication race can expose a partially initialized cpntf state to OFFLOAD_CANCEL, causing a kernel oops and leaving an unresolved active object lifetime violation that requires manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a remotely reachable NFSD race with an active structured object lifetime violation and UAF candidate behavior, not a pure resource leak or local admin-only cleanup bug.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: nfsd: fix cpntf publish race in nfs4_init_cp_state
Commit: 21d6c5957f5ca97d7352e60f55ea412beb9419f5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=21d6c5957f5ca97d7352e60f55ea412beb9419f5

Commit description:

nfs4_alloc_init_cpntf_state() published the new cpntf entry into the
s2s_cp_stateids IDR (with cs_type set) in one s2s_cp_lock section, then
took the lock again to list_add() it onto p_stid->sc_cp_list. In the gap
the entry is reachable by so_id but cp_list is still {NULL,NULL} from
kzalloc. A racing OFFLOAD_CANCEL (so_id is echoed to the client as
cnr_stateid, so any NFSv4.2 client can drive it) reaches
manage_cpntf_state() -> _free_cpntf_state_locked() and does list_del() on
the zeroed list_head, oopsing the server.

Fold the cs_type assignment and the list_add() into the same critical
section as idr_alloc_cyclic(), so a concurrent lookup either misses the
entry or sees a fully linked cp_list. INIT_LIST_HEAD() the entry after
allocation and switch _free_cpntf_state_locked() to list_del_init() so a
stale unlink is a no-op. nfs4_init_copy_state() passes NULL p_stid and
skips the list_add, preserving NFS4_COPY_STID semantics.

Fixes: 624322f ("NFSD add COPY_NOTIFY operation")
Cc: stable@vger.kernel.org
Assisted-by: kres:claude-opus-4-7
Signed-off-by: Chris Mason <clm@meta.com>
Link: https://patch.msgid.link/20260710-nfsd-testing-v3-1-a0ff7db6aa3e@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/nfsd/nfs4state.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=21d6c5957f5ca97d7352e60f55ea412beb9419f5

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

The original Linux kernel CVE announcement for CVE-2026-89684 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89684

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 6

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).