[CVE-2026-72219][MODERATE 7.0] lockd: Plug nlm_file leak when nlm_do_fopen() fails

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

CVE: CVE-2026-72219
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: lockd: Plug nlm_file leak when nlm_do_fopen() fails
Commit: bca74fff138429f3d5802865f38fc883d53a4f1a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bca74fff138429f3d5802865f38fc883d53a4f1a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72219
Analysis date: Sat, 15 Aug 2026 22:29:52 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A remotely reachable lockd error path leaks one `nlm_file` object whenever `nlm_do_fopen()` fails for a rejected file handle, allowing a network client to cause sustained kernel memory exhaustion and DoS on exposed NFS/NLM servers.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72219 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72219

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-72219	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '7.5';DESCR 'A remotely reachable memory leak in lockd can occur when nlm_lookup_file allocates an nlm_file and nlm_do_fopen later fails for a file handle rejected by the underlying export. A client can repeat this failure path so each rejected request leaks one nlm_file before it is inserted into nlm_files. For the CVSS the PR:N is used because a remote NLM client only needs network reachability to the lockd service and does not need local code execution on the target. The issue is network reachable on systems exposing NFS lockd or NLM services. Impact is denial of service through kernel memory exhaustion after sustained abuse. No direct confidentiality or integrity impact is indicated because this is a resource leak without an observed memory corruption primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	DISK INIT SIMPLEFIX LEAK  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

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

## 2. Signal breakdown

Conservative signals:

* **Remote reachable / network-triggerable: +2**
  lockd/NLM is a network service path. The commit says a client can repeatedly drive `nlm_do_fopen()` failures using rejected file handles.

* **Reliable resource-exhaustion DoS path: +1**
  Each failure leaks one freshly allocated `nlm_file`. Repetition can consume kernel memory.

* **Broad/common deployed exposure: +1**
  NFS/lockd is not Internet-facing in typical secure deployments, but it is common in enterprise and storage environments.

Paranoid additional signal:

* **Availability impact realistic: +1**
  Sustained remote triggering can plausibly lead to system-wide memory pressure or OOM conditions. This is still DoS-only, not memory corruption.

Not awarded:

* **No generic memory corruption**
  The bug is a leak on an error path, not UAF, double-free, OOB write, type confusion, or arbitrary write.

* **No privilege escalation signal**
  There is no supported reclaim, overwrite, stale callback, refcount takeover, or object confusion primitive.

* **No confidentiality or integrity impact**
  The leaked object is not exposed back to userspace and does not imply unauthorized read or write access.

## 3. Reachability analysis

A remote NFS/NLM client can potentially trigger the bug if lockd is exposed and the server accepts requests that reach `nlm_lookup_file()` with file handles rejected by the underlying export. No local code execution on the target is required, so practical PR is **PR:N** in CVSS terms. Network namespaces do not materially reduce the server-side impact once the service is reachable. The path is not enabled on every Linux system by default, but it is realistic on NFS servers using lockd/NLM, especially NFSv3-style locking deployments.

## 4. Severity interpretation

This behaves like an **actionable Moderate** issue rather than ordinary Low, because it is remotely reachable and repeatable. It is not an Important-class memory corruption issue because the patch only fixes a missing `kfree()` on an error path and does not show UAF, arbitrary write, attacker-controlled reuse, or privilege escalation. The realistic impact is remote kernel memory exhaustion DoS after sustained abuse.

## 5. One-sentence report phrase

A remotely reachable lockd error path leaks one `nlm_file` object whenever `nlm_do_fopen()` fails for a rejected file handle, allowing a network client to cause sustained kernel memory exhaustion and DoS on exposed NFS/NLM servers.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: the issue is network reachable and repeatable against exposed lockd/NLM services, even though the primitive is resource exhaustion only and does not currently support confidentiality, integrity, or privilege escalation impact.

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

Patch: lockd: Plug nlm_file leak when nlm_do_fopen() fails
Commit: bca74fff138429f3d5802865f38fc883d53a4f1a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bca74fff138429f3d5802865f38fc883d53a4f1a

Commit description:

A client can repeatedly drive nlm_do_fopen() failures by presenting
file handles that the underlying export rejects. After kzalloc_obj()
succeeds in nlm_lookup_file(), the freshly allocated nlm_file is not
yet inserted into nlm_files[]. The nlm_do_fopen() failure path jumps
to out_unlock, which releases nlm_file_mutex and returns without
freeing the allocation, so each failure leaks one nlm_file.

Route the failure through out_free so kfree() runs before the
function returns.

Fixes: 7f024fc ("Keep read and write fds with each nlm_file")
Cc: stable@vger.kernel.org
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=bca74fff138429f3d5802865f38fc883d53a4f1a

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

The original Linux kernel CVE announcement for CVE-2026-72219 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72219

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