* [CVE-2026-89484][LOW] lockd: fix NULL dereference on lockowner allocation failure
@ 2026-09-11 23:58 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-11 23:58 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89484
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: lockd: fix NULL dereference on lockowner allocation failure
Commit: 07adfbb3de7529f58ca708a97ead7fa4fdb71056
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=07adfbb3de7529f58ca708a97ead7fa4fdb71056
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89484
Analysis date: Fri, 11 Sep 2026 19:58:22 -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-2026-89484 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89484
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-2026-89484 LOW https://www.kernelcve.org/list/?q=CVE-2026-89484 CHECK WITH IMPACT FROM ORIG NN MODERATE 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-476;CWE-703;CWE-754;BEST CVSS score: '4.7';DESCR 'A NULL pointer dereference in the lockd NLM client path can occur when nlmclnt_find_lockowner fails to allocate a lockowner but the file lock still has NLM lock operations installed. The VFS then tears down the partially initialized file_lock and calls the NLM release callback, which dereferences a missing lock owner and can crash the kernel. For the CVSS the PR:L value is used because a local user or process with access to an NFS file that uses NLM locking can reach the affected path without full administrator privileges. AC:H is used because reliable triggering depends on an allocation failure or strong memory pressure during lock initialization. The issue is not directly network reachable and is triggered through local file locking behavior on an existing NFS mount. Impact is denial of service via kernel crash only.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) SKIP CVE-2026-89484 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE DANGER NULLPTR DISK SIMPLEFIX LINUS 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=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 2. No floor or cap applied.
* Raw paranoid score: 2
* Paranoid score: 2. No floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
Positive signals:
* +1 Reliable kernel crash / strong DoS. The commit directly describes a NULL pointer dereference in `nlmclnt_locks_release_private()` during VFS teardown of a partially initialized `file_lock`.
* +1 Local below-host-admin trigger. A local process with access to an already mounted NFS filesystem using NLM locking can reach the affected lock path without host administrator privileges.
Negative or limiting signals:
* No UAF signal awarded. The owner pointer was never allocated or installed, so this is a NULL dereference, not stale post-lifetime object use.
* No concrete repeated release/refcount signal awarded. There is no established first lifetime-ending release followed by a second lifetime mutation on the same dangling reference.
* No structured stale-object leverage awarded. The demonstrated operation is a release callback dereferencing a missing owner and faulting.
* No C/I impact awarded. The patch supports crash/DoS only, with no disclosure, arbitrary write, controlled reclaim, or privilege boundary bypass.
* No remote reachability awarded. The trigger is through local file locking behavior on an existing NFS/NLM client mount.
* No extra availability point awarded. The same kernel crash is already counted once.
Repeated release/refcount checklist:
* First release can end lifetime: not applicable.
* Exact same reference survives first release: not established.
* Second operation is a real lifetime/refcount mutation: not established.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no.
3. Reachability analysis
The vulnerable path is reached when NLM lock private state initialization fails because `nlmclnt_find_lockowner()` cannot allocate a lockowner. `nlmclnt_proc()` returns `-ENOMEM`, but VFS still tears down the partially initialized `file_lock` and calls `locks_release_private()`.
A local user or process with access to files on an already mounted NFS filesystem using NLM locking can plausibly exercise the affected file locking path. Reliable triggering additionally depends on allocation failure or strong memory pressure at the relevant point, which reduces practical exploitability but does not create a host-admin requirement.
This is not directly network-triggerable by packet input alone. Prior NFS mount setup is commonly administrator-provisioned, but the vulnerable operation itself can be reached by below-host-admin local users once such a mount exists. No namespace-scoped capability path is involved or required.
4. Primitive and severity interpretation
The exact primitive is a NULL pointer dereference caused by installing `nlmclnt_lock_ops` before the lockowner allocation is known to have succeeded. When the allocation fails, teardown later invokes the NLM release callback, and that callback dereferences `fl->fl_u.nfs_fl.owner` even though it is NULL.
This is Class C behavior: demonstrated crash/DoS from invalid state, without an independently useful corruption or lifetime primitive. It is not a real UAF, not a double free, and not a concrete repeated refcount mutation. The demonstrated consequence is kernel crash. Privilege escalation is not supported by the supplied patch or context.
ImportantCandidate=NO because the established primitive is NULL dereference DoS only and there is no meaningful unresolved memory corruption leverage. AutoDowngradeAllowed=YES because automatic downgrade would not discard a concrete UAF, boundary bypass, COW violation, controlled corruption, or repeated lifetime/refcount mutation.
5. One-sentence report phrase
A NULL pointer dereference in the lockd NLM client path can crash the kernel when lockowner allocation fails but NLM file lock operations remain installed during file_lock teardown.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
Reason: the patch-supported primitive is a local NULL pointer dereference with DoS impact only, and no UAF, repeated release/refcount mutation, controlled corruption, disclosure, or privilege escalation path is established.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: lockd: fix NULL dereference on lockowner allocation failure
Commit: 07adfbb3de7529f58ca708a97ead7fa4fdb71056
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=07adfbb3de7529f58ca708a97ead7fa4fdb71056
Commit description:
nlmclnt_locks_init_private() installs NLM file lock operations even when
nlmclnt_find_lockowner() fails to allocate a lockowner. nlmclnt_proc()
then returns -ENOMEM, but the VFS still tears down the partially
initialized file_lock and calls locks_release_private().
That invokes nlmclnt_locks_release_private(), which dereferences
fl->fl_u.nfs_fl.owner and crashes because the owner was never installed.
Clear fl_ops before attempting to initialize the NLM private state, and
install the NLM lock operations only after a lockowner has been allocated
successfully.
Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: [email protected]
Signed-off-by: Shuangpeng Bai <[email protected]>
Signed-off-by: Trond Myklebust <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/lockd/clntproc.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=07adfbb3de7529f58ca708a97ead7fa4fdb71056
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89484 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89484
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: Not available
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
^ permalink raw reply [relevance 21%]
Results 1-1 of 1 | reverse | sort options + mbox downloads above
-- links below jump to the message on this page --
2026-09-11 23:58 21% [CVE-2026-89484][LOW] lockd: fix NULL dereference on lockowner allocation failure AL-KERNEL
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox