* [CVE-2026-98963][MODERATE 7.0] btrfs: always return -EIOCBQUEUED after btrfs_uring_read_extent_endio [ Upstream
@ 2026-10-27 6:11 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-27 6:11 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98963
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: btrfs: always return -EIOCBQUEUED after btrfs_uring_read_extent_endio [ Upstream
Commit: 033dda5b321f01661de518a8d5c8607ae8675b14
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=033dda5b321f01661de518a8d5c8607ae8675b14
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98963
Analysis date: Tue, 27 Oct 2026 02:11:13 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
A failed synchronous Btrfs encoded read can cause immediate and deferred cleanup to unlock and free the same request state twice.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98963 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98963
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98963 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98963 CHECK WITH IMPACT FROM ORIG NN NONE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-415;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race dependent cleanup ownership bug in the Btrfs io_uring encoded read path can unlock and free the same request state twice. If all bios finish before btrfs_encoded_read_regular_fill_pages returns and the completed I/O status is negative, btrfs_uring_read_extent can perform error cleanup while btrfs_uring_read_finished performs deferred cleanup, creating a concrete double free or use-after-free candidate. Triggering is local and requires Btrfs encoded read support, io_uring access, an early bio completion window, and a failing I/O result, so AC:H is appropriate and there is no direct network reachability. For the CVSS the PR:L value in the paranoid score covers a constrained service or capability bearing process with delegated encoded read access, while the base uses PR:H for the normally privileged interface. Base C:L I:L A:H reflects kernel memory corruption lacking a demonstrated arbitrary write, while paranoid C:H I:H A:H is defensible because a double free may corrupt allocator state and potentially permit privilege escalation. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the manual review requirement was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK. The independent weaker Aegis shadow evaluated CVSS 2.6 and ActionableScore 4 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE DISK SIMPLEFIX SKIP IO_URING KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 3.
* Conservative score: 5. REAL UAF FLOOR 5 applies because the first cleanup may free the request state and a later deferred path cleans up the exact same state again.
* Raw paranoid score: 4.
* Paranoid score: 5. The same floor applies; no additional unsupported exploit effects are counted.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
* +2 Real UAF/lifetime violation: negative synchronous completion lets `btrfs_uring_read_extent()` unlock/free state already scheduled for cleanup by `btrfs_uring_read_finished()`.
* +1 Concrete repeated release/free: the first cleanup can end lifetime, the same request state survives into the deferred callback, and the second cleanup performs another unlock/free.
* +1 Plausible kernel crash/strong DoS from double free or stale cleanup.
* -1 Hard timing/state condition: all bios must finish before the fill function returns and produce a negative status.
* Paranoid +1: the second free is itself a write-like allocator/lifetime mutation through potentially freed storage. Controlled reclaim is not shown.
* FLOOR 5 applied; the repeated-lifetime exception prevents treating this as an ordinary cleanup fault.
Not awarded: local-unprivileged trigger, arbitrary write, controlled reclaim, confidentiality/integrity impact, LPE, extra availability, or authorization bypass.
3. Reachability analysis
The trigger is local through Btrfs encoded-read io_uring support and requires early failed-I/O completion. The supplied material characterizes the interface as normally privileged but does not show the exact capability check, UID requirement, namespace scope, or complete delegated-access path. Therefore host-admin and namespace-scoped reachability remain unknown. No remote path or special hardware requirement is shown.
4. Primitive and severity reading
This is an active request-state lifetime bug, not fixed stale storage. It is cleanup-path-specific, but it falls into concrete repeated lifetime corruption rather than a mere stale dereference: one path may free the state and the deferred path later frees the same state again. That establishes CLASS_B and plausible crash behavior. Allocator corruption beyond the second free is credible but uncontrolled; no Class A primitive or demonstrated LPE exists. ImportantCandidate is YES and auto-downgrade is disallowed because post-lifetime effects of the specific second free remain materially unresolved.
5. One-sentence report phrase
A failed synchronous Btrfs encoded read can cause immediate and deferred cleanup to unlock and free the same request state twice.
6. Manual review advice
MANUAL CHECK REQUIRED
Confirm interface privilege and whether repeatable triggering offers allocator-reuse leverage beyond denial of service.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: btrfs: always return -EIOCBQUEUED after btrfs_uring_read_extent_endio [ Upstream
Commit: 033dda5b321f01661de518a8d5c8607ae8675b14
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=033dda5b321f01661de518a8d5c8607ae8675b14
Changed files:
fs/btrfs/inode.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=033dda5b321f01661de518a8d5c8607ae8675b14
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98963 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98963
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:L/I:L/A:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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