* [CVE-2026-98907][LOW] btrfs: protect sb_write_pointer() with invalidate lock [ Upstream
@ 2026-10-27 4:45 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-27 4:45 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98907
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: btrfs: protect sb_write_pointer() with invalidate lock [ Upstream
Commit: c9b38f2eab5a9bd74087390318d93ccdd8d2deff
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c9b38f2eab5a9bd74087390318d93ccdd8d2deff
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98907
Analysis date: Tue, 27 Oct 2026 00:45:07 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A host-privileged BLKBSZSET race can disrupt Btrfs zoned superblock reads, but no memory-corruption or authorization primitive is demonstrated.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98907 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98907
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-2026-98907 LOW https://www.kernelcve.org/list/?q=CVE-2026-98907 CHECK WITH IMPACT FROM ORIG NN NONE | AEGIS IMPACT MODERATE AEGIS_AS=0 LEGACY=LOW RESULT=DIFF (final Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.1';DESCR 'A race in Btrfs zoned superblock handling allows sb_write_pointer to call read_cache_page_gfp while BLKBSZSET changes the block size and invalidates the block device page cache. The demonstrated primitive is an unsynchronized page cache read rather than UAF, OOB access, or an arbitrary write. For the CVSS the PR:H reflects that BLKBSZSET normally requires CAP_SYS_ADMIN and block device access, while AC:H reflects the need to hit a concurrent timing window. The supported impact is an erroneous superblock read or filesystem operation failure, with host wide denial of service retained only as the grounded worst case. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.1 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage LOW to LOW because the cross model evidence reconciliation rule was applied. 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. Exact triggered rule markers were V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 0 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) MAYBE DISK RACE SKIP HARDWARE V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 0.
* Conservative score: 0; no floor or cap applied.
* Raw paranoid score: 0.
* Paranoid score: 0; no technically supported stronger primitive.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Important filesystem/storage path: the race affects reading a Btrfs zoned-device superblock.
* +1 Availability plausible: an inconsistent page-cache read can cause an erroneous superblock result or filesystem-operation failure.
* -2 Proven host-administrator-equivalent prerequisite: changing a block device's logical block size through BLKBSZSET requires CAP_SYS_ADMIN and access to the affected block device.
* No race penalty: concurrency is required, but the evidence does not establish a sufficiently narrow or unrepeatable timing window beyond merely being a race.
* No reliable-crash point: panic or host-wide fatal failure is not demonstrated.
* No corruption point: the patch shows serialization of `read_cache_page_gfp()`, not a UAF, OOB access, write, or consumed corrupted structured state.
* B5-R does not apply: there is no retry-accumulated index or confirmed heap OOB write.
* B3-PENDING and B4-PENDING do not apply: no shared-backing write or authorization decision is involved.
3. Reachability analysis
The complete trigger requires concurrent superblock processing and BLKBSZSET against the same block device. BLKBSZSET is a privileged block-device management operation, establishing effective host-administrator-level access. Numeric UID 0 is not intrinsically required because the capability is the operative requirement. The supplied evidence does not establish a complete nested-namespace trigger, so namespace-scoped privilege remains unknown. No special hardware beyond a zoned Btrfs block device is shown.
4. Primitive and severity reading
The primitive is a synchronization defect permitting a page-cache read while block-size change invalidation is occurring. The supported result is an inconsistent read or operation failure, classified as CLASS_C invalid-state/availability behavior. No later dangerous consumer, memory corruption, protected-state change, or cross-boundary effect is shown. ImportantCandidate is therefore NO, and ordinary downgrade is safe.
5. One-sentence report phrase
A host-privileged BLKBSZSET race can disrupt Btrfs zoned superblock reads, but no memory-corruption or authorization primitive is demonstrated.
6. Manual review advice
NO MANUAL CHECK NEEDED
The patch and supplied context support only privileged race-induced invalid-read or availability behavior.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: btrfs: protect sb_write_pointer() with invalidate lock [ Upstream
Commit: c9b38f2eab5a9bd74087390318d93ccdd8d2deff
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c9b38f2eab5a9bd74087390318d93ccdd8d2deff
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=c9b38f2eab5a9bd74087390318d93ccdd8d2deff
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98907 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98907
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:H/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.1
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: 0
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).
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