[CVE-2026-98081][LOW] btrfs: zoned: finish active block group cleanup if call_zone_finish() fails [ Upstream

[CVE-2026-98081][LOW] btrfs: zoned: finish active block group cleanup if call_zone_finish() fails [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98081
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: btrfs: zoned: finish active block group cleanup if call_zone_finish() fails [ Upstream
Commit: 36b9cdab44848f25879ca625275c92b007f84653
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=36b9cdab44848f25879ca625275c92b007f84653
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98081
Analysis date: Fri, 25 Sep 2026 13:16:11 -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-2026-98081 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98081

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-2026-98081	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98081 CHECK WITH IMPACT FROM ORIG NN NONE	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-772;**CWE-400;CWE-703;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A failed zone finish operation in zoned Btrfs can leave an inactive block group linked on fs_info zone_active_bgs while retaining an extra reference. Waiters for BTRFS_FS_NEED_ZONE_FINISH may never be awakened, and btrfs_zone_finish_one_bg can repeatedly select the same block group because its alloc_offset has reached the zone capacity. This can make btrfs_zoned_activate_one_bg spin, consume CPU, and stall filesystem operations. For the CVSS the PR:L value reflects that a local user or process with write access may generate filesystem activity that reaches this path, although reliably forcing the underlying zone finish failure normally requires additional device conditions. The issue is not network reachable by itself and requires a mounted zoned Btrfs filesystem. Impact is denial of service through CPU spinning, blocked waiters, and degraded filesystem availability. No memory corruption primitive is visible, so confidentiality and integrity remain unaffected.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) 	MAYBE	DISK SIMPLEFIX LEAK SKIP 	-	-	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
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Concrete persistent kernel resource/reference leak. A failed `call_zone_finish()` leaves the block group on `zone_active_bgs` and retains its reference because normal cleanup is skipped.
* +1 Reliable strong DoS. The stale active-list entry is repeatedly selected, causing `btrfs_zoned_activate_one_bg()` to spin while zone-finish waiters remain blocked.
* +1 Important filesystem/storage path. The defect affects Btrfs zoned block-group allocation and zone-finish processing.
* -1 Rare and difficult-to-reach configuration. The vulnerable path specifically requires a mounted zoned Btrfs filesystem and a zone-finish failure on its backing storage.

Not awarded:

* No UAF, dangling dereference, repeated release, OOB access, or memory overwrite is established.
* No controlled reclaim, arbitrary write, information disclosure, or privilege escalation is demonstrated.
* No additional Availability point was awarded because the CPU spinning, blocked waiters, and filesystem stall are parts of the same DoS condition.
* No C/I impact was awarded. The inconsistent zone state is kept read-only after failure, and no unauthorized data modification is established.
* No remote-reachability or local-unprivileged bonus was awarded because an ordinary user may generate filesystem activity but is not shown to control the required zone-finish failure.

3. Reachability analysis

The path requires a previously configured and mounted zoned Btrfs filesystem. Such setup normally involves an administrator, but the evidence does not establish whether the attacker must possess host-administrator privileges at trigger time. A user with write access may generate allocation pressure that reaches zone finishing, while the decisive `call_zone_finish()` failure depends on the backing device or storage stack and is not shown to be reliably attacker-controlled.

The complete trigger is not established as namespace-scoped. No direct network trigger exists. Zoned storage or an equivalent emulated setup is required. This is a deterministic error-path cleanup defect rather than a race, so no timing penalty applies.

4. Primitive and severity interpretation

The exact primitive is a persistent block-group reference leak combined with invalid active-list membership and failure to wake waiters. The block group remains allocated rather than being freed and subsequently reused, so this is not a UAF or repeated lifetime mutation through a dangling reference.

The bug is CLASS_C because its demonstrated behavior is resource leakage, CPU spinning, blocked waiters, and filesystem unavailability without an independently useful corruption primitive. The practical consequence is DoS affecting the zoned Btrfs filesystem and potentially system responsiveness. Stronger confidentiality, integrity, or privilege-escalation consequences are unsupported.

ImportantCandidate is NO because there is no memory-corruption, ownership-bypass, or authorization primitive requiring Important-grade preservation. AutoDowngradeAllowed is YES because the issue is a specialized error-path DoS and reference leak with no unresolved exploitation leverage beyond availability impact.

5. One-sentence report phrase

A failed zone-finish operation can leave a referenced Btrfs block group on the active list, causing repeated selection, CPU spinning, blocked waiters, and denial of service without an established memory-corruption primitive.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a constrained resource/reference leak and availability failure in zoned Btrfs, with no UAF, memory corruption, security-boundary bypass, or plausible confidentiality or integrity primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: btrfs: zoned: finish active block group cleanup if call_zone_finish() fails [ Upstream
Commit: 36b9cdab44848f25879ca625275c92b007f84653
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=36b9cdab44848f25879ca625275c92b007f84653

Changed files:
  fs/btrfs/zoned.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=36b9cdab44848f25879ca625275c92b007f84653

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

The original Linux kernel CVE announcement for CVE-2026-98081 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98081

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:L/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).