[CVE-2026-89715][LOW] NFS/localio: fix ref leak on nfs_uuid_add_file failure

[CVE-2026-89715][LOW] NFS/localio: fix ref leak on nfs_uuid_add_file failure

[AL-KERNEL]

CVE: CVE-2026-89715
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: NFS/localio: fix ref leak on nfs_uuid_add_file failure
Commit: 5215e734bf7cba18237155f8cb2a0accb60ca339
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5215e734bf7cba18237155f8cb2a0accb60ca339
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89715
Analysis date: Fri, 11 Sep 2026 21:11:58 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89715 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89715

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: LOW
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-2026-89715	LOW	https://www.kernelcve.org/list/?q=CVE-2026-89715 CHECK WITH IMPACT FROM ORIG NN LOW	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-362;*CWE-401;*CWE-772;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A reference leak in the NFS localio path can occur when nfs_uuid_add_file races with nfs_uuid_put during uuid net teardown and returns ENXIO before nfl nfs_uuid is published. In that failure path nfs_close_local_fh will later early return and cannot release the resources that were never attached to the slot. The leaked references can pin an nfsd_file and its underlying file, dentry, inode, and an nfsd_net reference, which may block nfsd_net or netns teardown and cause denial of service through resource retention. For the CVSS the PR:L is used for the paranoid score because a less privileged local actor may trigger NFS operations in environments where localio and namespace teardown are delegated, but reliable triggering still requires a local execution context. The issue is not directly network reachable because it is tied to localio and local teardown behavior rather than ordinary remote NFS traffic. Impact is denial of service only, with no supported confidentiality or integrity impact from the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)  SKIP CVE-2026-89715 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	DISK RACE LEAK NETWORK  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap changed the score.

2. Signal breakdown

Positive signals:

* +1 Concrete persistent kernel resource/reference leak. The patch establishes missing release of a caller-owned nfsd_file reference and an associated nfsd_net reference when nfs_uuid_add_file fails before publishing nfl->nfs_uuid.
* +1 Availability/resource-retention impact. The leaked nfsd_file, underlying file, dentry, inode, and nfsd_net reference can block nfsd_net or netns teardown.

Negative signals:

* No negative privilege penalty applied. Host-admin-equivalent triggering is plausible but not positively established by the supplied evidence.
* No race penalty applied. A race is present, but the supplied evidence does not prove a materially narrow or unreliably triggerable timing window sufficient for a scoring subtraction.

Important non-awarded signals:

* RealUAF not awarded. The described bug is a missing put/reference leak, not post-free use of an object.
* Concrete repeated release/refcount not awarded. The patch adds missing puts for leaked references, but the vulnerable behavior is not a second put on the same potentially dangling reference.
* First release can end lifetime: not applicable for repeated-release scoring.
* Exact same reference survives to a second lifetime mutation: no.
* Second operation is a real lifetime/refcount mutation on a dangling reference: no.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity impact not awarded.
* Remote reachability not established.
* Extra availability not awarded beyond the resource-retention effect.

3. Reachability analysis

The vulnerable path is in NFS localio cleanup/error handling when nfs_uuid_add_file races with nfs_uuid_put during uuid net teardown. Triggering requires NFS localio activity plus teardown of the relevant uuid or network context. The supplied evidence does not establish that an ordinary unprivileged local user can complete the full trigger chain.

Host-admin-equivalent setup is plausible because NFS localio, nfsd state, and network namespace teardown are typically managed by privileged components, but the evidence does not positively prove host-admin is required for every relevant deployment. Therefore HostAdminRequired is UNKNOWN.

NamespaceScopedPrivilege is UNKNOWN. The issue mentions netns teardown, but the supplied context does not prove that all required operations are namespace-scoped and attacker-obtainable below host admin.

Prior privileged setup may exist in practical deployments because NFS localio and nfsd configuration are not ordinary user operations, but this is not scored as a concrete negative without full evidence.

No special hardware prerequisite is indicated. The race appears tied to teardown and reference publication, but no hard one-shot timing penalty is proven.

4. Primitive and severity interpretation

The exact primitive is a persistent reference leak in an NFS localio error path. When nfs_uuid_add_file returns ENXIO before nfl->nfs_uuid is published, nfs_close_local_fh later cannot clean up because it observes a NULL nfs_uuid and returns early. The missing cleanup leaks a caller-owned nfsd_file reference and an embedded nfsd_net reference.

This is not active structured stale-object use and not fixed stale storage UAF. It is a resource/lifetime accounting defect whose demonstrated consequence is resource retention and blocked teardown.

There is no concrete repeated release/refcount operation. This is not category B second lifetime/refcount mutation through a dangling object. It is a missing release that prevents lifetime teardown.

PrimitiveClass is CLASS_C because the demonstrated behavior is DoS/resource-retention without an independently useful corruption primitive. ImportantCandidate is NO because no UAF, arbitrary write, controlled reclaim, authorization bypass, COW violation, or privilege-escalation path is supported. AutoDowngradeAllowed is YES because the issue is a constrained reference leak with DoS-only impact and no unresolved corruption primitive requiring Important-vs-Moderate review.

Likely operational severity is ordinary Moderate or Low-like depending on deployment exposure and ability to repeatedly trigger the teardown race.

5. One-sentence report phrase

An NFS localio error path can leak nfsd_file and nfsd_net references when nfs_uuid_add_file races with nfs_uuid_put before nfl nfs_uuid is published, potentially blocking nfsd_net or netns teardown and causing a local denial of service.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the patch supports a concrete reference leak and teardown DoS only, with no Real UAF, repeated lifetime mutation, memory corruption, authorization bypass, or plausible privilege-escalation primitive.

7. Call-site confidence

Call-site confidence: medium

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

Patch: NFS/localio: fix ref leak on nfs_uuid_add_file failure
Commit: 5215e734bf7cba18237155f8cb2a0accb60ca339
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5215e734bf7cba18237155f8cb2a0accb60ca339

Commit description:

When nfs_uuid_add_file() races with nfs_uuid_put() tearing down
uuid->net, it returns -ENXIO without publishing nfl->nfs_uuid via
rcu_assign_pointer().  nfs_open_local_fh() then enters its error
branch and only releases the slot's file ref and its paired net
ref plus its own entry-time net ref, while the close path is a
no-op:

    nfs_close_local_fh()
      nfs_uuid = rcu_dereference(nfl->nfs_uuid);
      if (!nfs_uuid) { rcu_read_unlock(); return; }  /* always */

nfsd_open_local_fh() returns localio holding a caller-owned +1
nfsd_file reference (from nfsd_file_get() after
nfsd_file_acquire_local()) and an entry-time nfsd_net reference
(from its first nfsd_net_try_get()) embedded as nf->nf_net.  Both
are leaked on the failure path, pinning one nfsd_file (and the
underlying struct file, dentry, inode) and one nfsd_net_ref per
occurrence, which blocks nfsd_net and netns teardown.

Fix by releasing the caller-owned file ref and its net ref through
the existing helper, using a stack-local RCU pointer so the helper
can xchg it out, then returning -ENXIO so callers do not
dereference a localio whose slot has been cleared:

    struct nfsd_file __rcu *tmp = RCU_INITIALIZER(localio);

    nfs_to_nfsd_file_put_local(pnf);
    nfs_to_nfsd_file_put_local(&tmp);
    localio = ERR_PTR(-ENXIO);

The trailing nfs_to_nfsd_net_put(net) continues to release the
outer net ref, so all three nfsd_net_try_get() increments are
balanced on the error branch.

Fixes: fdd015d ("NFS/localio: nfs_uuid_put() fix races with nfs_open/close_local_fh()")
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/20260602-nfsd-testing-v2-3-e4ea62e3cd5c@kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/nfs_common/nfslocalio.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=5215e734bf7cba18237155f8cb2a0accb60ca339

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

The original Linux kernel CVE announcement for CVE-2026-89715 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89715

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:H/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: unknown
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).