[CVE-2026-98444][LOW] xfs: drop dquot flush lock when we can't find a buffer to flush

[CVE-2026-98444][LOW] xfs: drop dquot flush lock when we can't find a buffer to flush

[AL-KERNEL]

CVE: CVE-2026-98444
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: xfs: drop dquot flush lock when we can't find a buffer to flush
Commit: 41bc624377f08125eae164c62ce043791ade93b7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=41bc624377f08125eae164c62ce043791ade93b7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98444
Analysis date: Mon, 19 Oct 2026 00:05:48 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A missing dquot flush unlock in the XFS quota error path can leave quota state permanently locked and stall later flush, synchronization, or unmount operations, resulting in a local availability failure without evidence of memory corruption or privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98444 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98444

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-98444	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98444 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=1 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both 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-667;CWE-755;*CWE-833;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'xfs_qm_flush_one can leave the dquot flush lock permanently held when xfs_dquot_use_attached_buf fails or no attached buffer is found. Since no buffer exists to complete the flush and release the lock, later quota flush, filesystem synchronization, or unmount operations may block and cause an availability failure. For the CVSS the PR:L value is used in the paranoid score because a local user subject to XFS quotas may be able to influence quota activity and indirectly reach the vulnerable flush path, although reliable control of the missing buffer condition is not demonstrated. AC:H reflects the need to reach a specific internal error state that is not directly controlled through a normal user interface. The issue is not network reachable. Impact is limited to denial of service because the code shows a retained lock rather than a UAF, OOB access, information disclosure, or arbitrary write primitive. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 1.7 and ActionableScore 1 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	LOCK DISK SIMPLEFIX LINUS 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Positive signals:

* +1 Reliable strong DoS. Failure to release the dquot flush lock can leave it permanently held, causing later quota flush, synchronization, or unmount operations to stall.
* +1 Important filesystem path. The defect affects XFS quota metadata flushing and can impair filesystem management operations.

Negative signals:

* No negative points were applied. The complete attacker privilege and trigger boundary are unresolved, so no speculative host-admin, rarity, or timing penalty is used.

Important non-awarded signals:

* No UAF, OOB access, repeated release, refcount corruption, arbitrary write, or controlled reclaim is established.
* No confidentiality, integrity, authorization-bypass, cross-file ownership, or privilege-escalation primitive is established.
* No additional availability point is awarded because persistent dqflock retention and the resulting stall are the same availability mechanism.
* B5-R does not apply because there is no heap OOB write or retry-accumulated offset.
* B3-PENDING does not apply because there is no shared-backing write.
* B4-PENDING does not apply because no DENY-to-ALLOW authorization decision changes.
* V32, V33, and V34 do not apply because no skb checksum metadata write or networking trust boundary exists.

3. Reachability analysis

The vulnerable path requires an XFS filesystem using quotas and an execution of `xfs_qm_flush_one()` where `xfs_dquot_use_attached_buf()` fails or returns no buffer. Mounting and configuring the filesystem normally involves prior administrator activity, but that does not prove that the actor indirectly provoking the later quota flush must itself have host-admin privileges.

An ordinary user subject to XFS quotas can generate quota activity, but the supplied evidence does not establish that such a user can reliably create the missing-buffer condition. Therefore `HostAdminRequired` remains `UNKNOWN` rather than being assumed `YES` or `NO`.

No user-namespace or namespace-scoped capability path is demonstrated. There is no network trigger, special hardware requirement, or race. The defect is a deterministic error-path cleanup omission once the internal failure state occurs.

4. Primitive and severity interpretation

The exact primitive is failure to release `dqflock` on two error exits. The affected dquot remains live, but its flush lock can remain permanently held because no buffer exists to complete the normal flush and unlock sequence.

This is invalid-state and lock-retention behavior, not stale storage or an active-object lifetime violation. There is no first operation ending object lifetime, no dangling reference, and no second lifetime or refcount mutation. It is therefore `CLASS_C`, not `CLASS_B` or `CLASS_A`.

The demonstrated consequence is a permanently locked dquot with plausible quota-processing or filesystem-operation stalls. A kernel panic, filesystem corruption, disclosure, unauthorized modification, and privilege escalation are not supported. `ImportantCandidate=NO` and `AutoDowngradeAllowed=YES` because no unresolved corruption or security-boundary primitive would be lost by ordinary Moderate handling.

5. One-sentence report phrase

A missing dquot flush unlock in the XFS quota error path can leave quota state permanently locked and stall later flush, synchronization, or unmount operations, resulting in a local availability failure without evidence of memory corruption or privilege escalation.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a lock-retention DoS condition only, with no memory-corruption, authorization, ownership, or cross-boundary primitive.

7. Call-site confidence

Call-site confidence: medium

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

Patch: xfs: drop dquot flush lock when we can't find a buffer to flush
Commit: 41bc624377f08125eae164c62ce043791ade93b7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=41bc624377f08125eae164c62ce043791ade93b7

Commit description:

LOLLM noticed that xfs_qm_flush_one fails to drop the dquot flush lock
if it can't grab the buffer associated with the dquot.  Since there's no
buffer, nobody else is going to drop the dqflock, so we need to do it
ourselves.

Cc: stable@vger.kernel.org # v6.13
Fixes: ca37818 ("xfs: convert quotacheck to attach dquot buffers")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/xfs/xfs_qm.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=41bc624377f08125eae164c62ce043791ade93b7

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

The original Linux kernel CVE announcement for CVE-2026-98444 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98444

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).