[CVE-2026-97548][MODERATE 7.0] xfs: fix the rtrmap and rtrefcount _maxlevels_ondisk functions

[CVE-2026-97548][MODERATE 7.0] xfs: fix the rtrmap and rtrefcount _maxlevels_ondisk functions

[AL-KERNEL]

CVE: CVE-2026-97548
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: xfs: fix the rtrmap and rtrefcount _maxlevels_ondisk functions
Commit: 108114437915e61e8f88d1cbcc442c3f886a347e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=108114437915e61e8f88d1cbcc442c3f886a347e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97548
Analysis date: Sat, 26 Sep 2026 14:25:59 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-97548 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97548

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-2026-97548	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97548 CHECK WITH IMPACT FROM ORIG NN 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:H/I:H/A:H';CWE-131;*CWE-787;CWE-125;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'The XFS realtime rmap and refcount maximum level calculations omit the inode root level when sizing in memory btree cursors. A sufficiently large on disk btree can therefore have one more level than the allocated cursor supports, allowing XFS to access memory beyond the end of the cursor. This is a potential kernel memory corruption condition that can cause a kernel crash, filesystem metadata corruption, or other integrity and confidentiality impact. In the worst defensible case the out of bounds access may support local privilege escalation, although a controllable write primitive is not established by the available code change. For the CVSS the PR:L value is used for the paranoid score because a local user with write access to an already mounted and suitably configured XFS filesystem may be able to exercise btree operations without having mount privileges. The attack complexity is high because XFS realtime rmap or refcount support and a btree large enough to reach the underestimated maximum depth are required. The issue is not directly network reachable.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 4)  SKIP CVE-2026-97548 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	DISK SIMPLEFIX HARDWARE LINUS  INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
ActionableScoreLower=3
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap was applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Conservative signals:

* +1 Weak or indirect corruption candidate. Omitting the inode-root level underallocates the variable-depth XFS btree cursor and permits access beyond its allocated per-level state.
* +1 Reliable kernel crash or strong DoS. Reaching a nonexistent cursor level can access unrelated kernel memory and realistically cause an Oops, panic, assertion, or XFS shutdown.
* +1 Important filesystem and storage path. The affected cursors operate on XFS realtime reverse-mapping and reference-count metadata.
* Raw conservative total: 1 + 1 + 1 = 3.

Additional paranoid signals:

* +1 Weak LPE concern. Normal btree cursor processing updates active per-level state, so an undersized cursor plausibly permits a write-like access into adjacent kernel memory. The available patch does not establish payload or target control.
* +1 Integrity plausible. Corruption of cursor state during rtrmap or rtrefcount processing can plausibly misdirect later metadata processing and damage filesystem metadata outside the file data the triggering user is authorized to modify.
* Raw paranoid total: 3 + 1 + 1 = 5.

Important non-awarded signals:

* No strong corruption +2 was awarded because an attacker-influenced OOB write with meaningful payload or target control is not directly established.
* No local-unprivileged bonus was awarded. A user with write access may exercise btree operations on an already mounted filesystem, but the complete path to the required maximum depth is not shown.
* No host-admin penalty was applied because host administration is required to provision and mount the filesystem, but it is unresolved whether administration is required for the final triggering operation.
* No rare-configuration penalty was applied. The realtime rmap and refcount configuration is specialized, but rarity alone does not prove that an attacker cannot reach an existing deployment.
* No remote-reachability, arbitrary-write, controlled-reclaim, disclosure, COW-boundary, or demonstrated privilege-escalation signal was awarded.
* The crash was counted once. No duplicate Availability point was added.
* This is not a UAF and no repeated release or refcount signal applies.

3. Reachability analysis

A suitable XFS filesystem must use the affected realtime rmap or realtime refcount btree format and must contain a sufficiently large btree to reach the omitted inode-root level. Creating and mounting that filesystem is prior privileged setup.

After mounting, ordinary filesystem operations can invoke XFS btree cursors. A local user with write access might therefore reach the vulnerable processing without mount privileges, but the supplied patch does not establish that such a user can independently grow or shape the affected btree to the required depth. HostAdminRequired is consequently UNKNOWN rather than YES or NO.

No user-namespace or namespace-scoped capability path is supplied. NamespaceScopedPrivilege is UNKNOWN. There is no race requirement, special hardware requirement, or direct network trigger. Access through NFS or another remote filesystem frontend would be indirect and does not establish reliable remote control over the required realtime metadata shape.

4. Primitive and severity interpretation

The exact primitive is an undersized in-memory XFS btree cursor followed by an access beyond its allocated per-level storage. This is active structured state used during btree traversal and modification, not fixed stale storage and not a cleanup-only invalid pointer.

The evidence directly establishes an OOB access but does not identify every affected cursor operation or prove whether the first invalid operation is a read, write, or both. Normal cursor semantics make a write-like OOB access technically plausible, but controlled destination, controlled payload, arbitrary kernel write, and privilege escalation are not established.

This is CLASS_B because a concrete active kernel object can be accessed outside its allocation and exploitation-leverage analysis remains necessary. The demonstrated practical consequences are kernel failure and possible XFS shutdown. Filesystem metadata corruption and local privilege escalation are plausible worst cases, but only metadata integrity receives a paranoid point and LPE itself is not scored as demonstrated.

ImportantCandidate is YES because the unresolved access direction and the active cursor fields can distinguish an ordinary crash from exploitable adjacent-object corruption. AutoDowngradeAllowed is NO because automatically closing the issue as crash-only would discard that unresolved kernel-corruption primitive. The likely operational severity is Actionable Moderate unless call-site analysis confirms meaningful control over an OOB write, in which case Important classification may be warranted.

5. One-sentence report phrase

An underestimated XFS realtime btree cursor size can cause out-of-bounds access to active kernel cursor state on sufficiently deep trees, resulting in kernel failure or filesystem metadata corruption and requiring manual review for possible write-side exploitation leverage.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Review the allocation layout and all accesses to the highest rtrmap and rtrefcount cursor level to determine whether the overflow is a read, a write, or both, what adjacent allocation fields are reached, and whether an unprivileged filesystem writer can create the required btree depth.

7. Call-site confidence

Call-site confidence: medium

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

Patch: xfs: fix the rtrmap and rtrefcount _maxlevels_ondisk functions
Commit: 108114437915e61e8f88d1cbcc442c3f886a347e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=108114437915e61e8f88d1cbcc442c3f886a347e

Commit description:

The _maxlevels_ondisk functions are used to compute the size of
in-memory btree cursors for each btree type.  Unfortunately, LOLLM
noticed that the rtrmap and rtrefcount versions of these functions
forget to account for the inode root, which means that we could access
beyond the end of the cursor given a sufficiently large btree.  Fix
this.

Cc: stable@vger.kernel.org # v6.14
Fixes: 9abe03a ("xfs: introduce realtime refcount btree ondisk definitions")
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/libxfs/xfs_rtrefcount_btree.c
  fs/xfs/libxfs/xfs_rtrmap_btree.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=108114437915e61e8f88d1cbcc442c3f886a347e

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

The original Linux kernel CVE announcement for CVE-2026-97548 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97548

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: 3
  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: NO
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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).