[CVE-2026-97545][MODERATE REGULAR] xfs: don't leak new_bp if xfs_btree_bload_drop_buf fails

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-97545
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: xfs: don't leak new_bp if xfs_btree_bload_drop_buf fails
Commit: 355b8a5d7e9a38fca8dbf7a4721450252ac7868f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=355b8a5d7e9a38fca8dbf7a4721450252ac7868f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97545
Analysis date: Mon, 28 Sep 2026 18:24:07 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
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-2026-97545 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97545

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 REGULAR
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-2026-97545	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97545 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:H/UI:N/S:U/C:N/I:N/A:H';*CWE-772;CWE-404;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.1';DESCR 'An error path in xfs_btree_bload_prep_block can lose the reference to a locked new_bp buffer when xfs_btree_bload_drop_buf fails while writing the delayed write buffer list. The retained locked buffer can consume resources and may block later XFS operations, filesystem maintenance, or unmount processing. For the CVSS the PR:H value is used because reliable triggering normally requires administrative control over the relevant XFS btree operation or the storage failure conditions. AC:H applies because the vulnerable path also depends on an I/O failure at a specific stage of btree construction. The issue is not directly network reachable. The demonstrated impact is resource retention and reduced availability rather than UAF, out of bounds access, information disclosure, or privilege escalation. The worst defensible impact is a filesystem stall or denial of service if the lost locked buffer prevents further progress.';NO MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) 	MAYBE	DISK SIMPLEFIX LEAK LINUS  INCREASED_FROM_LOW_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN3 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Conservative signals:

* +1 Concrete persistent kernel resource/reference leak. On the error path, the acquired and locked `new_bp` is lost without `xfs_buf_relse()`.
* +1 Important filesystem/storage path. The defect affects XFS staged btree construction and metadata-buffer lifetime management.
* Total: 2.

Additional paranoid signal:

* +1 Strong DoS concern. Retaining a permanently locked XFS buffer can plausibly block later access to that buffer or interfere with filesystem maintenance and unmount processing.
* Total: 3.

Non-awarded signals:

* No UAF exists. The buffer is retained rather than freed and subsequently accessed.
* No repeated release or post-lifetime refcount mutation exists.
* No metadata overwrite, arbitrary write, controlled reclaim, disclosure, or authorization bypass is established.
* No filesystem integrity point was awarded because the patch establishes a leaked locked buffer, not persistent on-disk metadata corruption.
* No additional availability point was awarded beyond the paranoid lock-stall concern.
* No privilege penalty was applied because the supplied patch does not expose the complete call chain or positively establish host-admin-equivalent privilege.
* No remote or local-unprivileged reachability bonus was awarded.

3. Reachability analysis

The vulnerable path requires `xfs_btree_bload_drop_buf()` to encounter an I/O error while a staged XFS btree is being formatted. The supplied context does not show the callers that initiate this operation or the exact capability check governing them.

Staged btree construction is commonly associated with administrative metadata repair or rebuild operations, but that observation alone is insufficient to mark host administration as positively established under the scoring rules. The attacker must also be able to reach the relevant operation and cause or coincide with a write failure at this specific stage.

There is no evidence that an ordinary user can force the complete sequence, that a user-namespace capability is sufficient, or that the operation is namespace scoped. There is no direct network trigger, race condition, special hardware requirement, or demonstrated attacker-controlled I/O-failure mechanism.

4. Primitive and severity interpretation

The exact primitive is a concrete resource and lock leak. `new_bp` remains allocated and locked when `xfs_btree_bload_drop_buf()` fails, because the error path returns without releasing it.

This is not stale post-lifetime storage, UAF, double release, or memory corruption. The object remains alive, and the missing operation is the first required release. Therefore, the repeated-release exception and UAF floors do not apply.

The defect is classified as CLASS_C because its security-relevant consequence is constrained resource retention and potential filesystem stalling without an independently useful corruption primitive. The demonstrated result is a lost locked buffer. A broader XFS stall is a defensible paranoid consequence, while privilege escalation, confidentiality loss, and persistent metadata corruption are unsupported.

ImportantCandidate is NO because no Important-grade corruption, ownership, authorization, or lifetime-after-free primitive exists. AutoDowngradeAllowed is YES because the issue can be handled as a constrained availability defect after confirming product exposure.

5. One-sentence report phrase

An XFS staged btree error path can lose a locked buffer after a delayed write failure, causing a persistent resource leak and potentially blocking later filesystem operations.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm the reachable callers, required privilege, and whether the retained lock can cause lasting filesystem-wide unavailability beyond the underlying I/O failure.

7. Call-site confidence

Call-site confidence: medium

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

Patch: xfs: don't leak new_bp if xfs_btree_bload_drop_buf fails
Commit: 355b8a5d7e9a38fca8dbf7a4721450252ac7868f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=355b8a5d7e9a38fca8dbf7a4721450252ac7868f

Commit description:

LOLLM observes that in xfs_btree_bload_prep_block,
xfs_btree_bload_drop_buf can hit an IO error if writing the delwri
buffer list to disk fails.  In this case, we fail to release new_bp,
which means we lose a locked buffer.  Fix that.

Cc: stable@vger.kernel.org # v6.8
Fixes: e069d54 ("xfs: constrain dirty buffers while formatting a staged btree")
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_btree_staging.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=355b8a5d7e9a38fca8dbf7a4721450252ac7868f

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

The original Linux kernel CVE announcement for CVE-2026-97545 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97545

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: 2
  Paranoid ActionableScore: 3

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 REGULAR

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).