[CVE-2026-97546][LOW] xfs: don't spin forever on zero-length dirents when salvaging them

[CVE-2026-97546][LOW] xfs: don't spin forever on zero-length dirents when salvaging them

[AL-KERNEL]

CVE: CVE-2026-97546
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: xfs: don't spin forever on zero-length dirents when salvaging them
Commit: 5442f0c56445618544a801fb4dae35aed87a1aaa
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5442f0c56445618544a801fb4dae35aed87a1aaa
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97546
Analysis date: Fri, 25 Sep 2026 13:08:53 -0400
ActionableScore: 0
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-2026-97546 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97546

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-2026-97546	LOW	https://www.kernelcve.org/list/?q=CVE-2026-97546 CHECK WITH IMPACT FROM ORIG NN 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:L';*CWE-835;*CWE-20;**CWE-400;BEST CVSS score: '1.9';DESCR 'An infinite loop in XFS directory online repair can occur when xrep_dir_recover_data processes corrupted directory metadata containing an unused dirent or normal entry with zero length. The recovery loop does not advance its offset and can consume CPU until the repair operation is terminated. For the CVSS the PR:H reflects that reliably reaching this path normally requires administrative control of XFS online repair and an XFS filesystem with crafted or corrupted on disk metadata. The issue is not network reachable. Impact is limited to local denial of service through a stuck repair task and CPU consumption. No memory corruption or privilege escalation primitive is indicated.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	YES	DISK SIMPLEFIX LINUS  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS	YES	NO	checked

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

ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: -1
* Conservative score: 0
* Raw paranoid score: -1
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate**::

The score is clamped to zero because the raw arithmetic is negative. No floor or cap was applied.

2. Signal breakdown

* +1 Reliable local CPU consumption. A zero length unused dirent or a normal entry with a zero computed size prevents `offset` from advancing, causing the online directory repair loop to revisit the same metadata indefinitely.
* -2 Host-admin-equivalent requirement. XFS online repair is an administrative filesystem operation, and reliably supplying crafted on-disk XFS directory metadata requires control of the filesystem image, backing block device, or equivalent privileged mount and repair environment.

Important non-awarded signals:

* No UAF, stale reference, double release, refcount mutation, OOB access, or other memory-corruption primitive is established.
* No controlled reclaim, arbitrary write, structured object replacement, disclosure, integrity violation, or privilege-escalation path is demonstrated.
* No remote reachability is established. The vulnerable loop is reached through local XFS online repair processing.
* No additional availability point is awarded. The CPU loop is the same DoS condition already counted above, and `xchk_should_terminate()` is checked in every iteration, allowing the repair operation to be interrupted.
* No filesystem ownership or COW security-boundary violation is established. The malformed directory metadata affects repair traversal progress only.

3. Reachability analysis

The triggering condition is a corrupted XFS directory block containing a zero length unused dirent or an entry whose computed size is zero. The affected function is in the XFS online directory repair path, not ordinary directory lookup or normal packet or file data processing.

A complete reliable trigger normally requires an actor able to run XFS online repair and provide or alter malformed filesystem metadata. This is host-admin-equivalent in the normal XFS deployment model because online repair and control of the mounted filesystem or its backing storage are administrative operations.

The complete operation is not namespace-scoped. A user namespace or network namespace does not provide sufficient control over a host XFS mount, its repair interface, and the malformed backing metadata. No special hardware, boot parameter, race condition, or network exposure is involved.

4. Primitive and severity interpretation

The exact primitive is a non-advancing loop over malformed directory metadata. When `dup->length` is zero, the old code executes `offset += 0` and continues. When `xfs_dir2_data_entsize()` returns zero, the old code similarly leaves `offset` unchanged. The result is CPU consumption in the XFS repair operation.

This is neither active structured-object lifetime corruption nor fixed stale storage. There is no release, free, put, refcount decrement, stale dereference, or second lifetime mutation. It is a validation and loop-progress defect.

PrimitiveClass is NONE because the patch establishes no meaningful corruption, ownership, authorization, lifetime, or security-boundary primitive. The demonstrated consequence is a stuck repair task consuming CPU until terminated. A broader host-wide DoS, confidentiality impact, integrity impact, or privilege escalation is speculative and unsupported.

ImportantCandidate is NO because this is a constrained administrative repair-path loop with no demonstrated exploitation leverage beyond CPU consumption. AutoDowngradeAllowed is YES because automatic low-priority handling would not discard a concrete unresolved kernel-corruption or boundary-bypass primitive.

5. One-sentence report phrase

A malformed zero length XFS directory entry can cause XFS online directory repair to loop without advancing its offset and consume CPU until the repair task is terminated.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch fixes a bounded-class validation failure in an administrative XFS online repair path. No memory-corruption, authorization, ownership, or privilege-escalation primitive is established.

7. Call-site confidence

Call-site confidence: high

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

Patch: xfs: don't spin forever on zero-length dirents when salvaging them
Commit: 5442f0c56445618544a801fb4dae35aed87a1aaa
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5442f0c56445618544a801fb4dae35aed87a1aaa

Commit description:

LOLLM noticed that xrep_dir_recover_data can spin forever if it
encounters an unused dirent that claims to have length zero.  Fix that,
and prevent the same thing from happening with a zero-length entry.

Cc: stable@vger.kernel.org # v6.10
Fixes: b1991ee ("xfs: online repair of directories")
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/scrub/dir_repair.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=5442f0c56445618544a801fb4dae35aed87a1aaa

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

The original Linux kernel CVE announcement for CVE-2026-97546 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97546

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 1.9

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).