* [CVE-2026-97542][LOW] xfs: bail out on bitmap errors in xrep_agfl_fill
@ 2026-09-26 19:46 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-26 19:46 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-97542
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: xfs: bail out on bitmap errors in xrep_agfl_fill
Commit: e49977bc568c2649cf1a37992e538df8e3779ee4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e49977bc568c2649cf1a37992e538df8e3779ee4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97542
Analysis date: Sat, 26 Sep 2026 15:46:54 -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-2026-97542 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97542
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-2026-97542 LOW https://www.kernelcve.org/list/?q=CVE-2026-97542 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:L/A:H';CWE-252;CWE-703;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '4.7';DESCR 'An XFS online repair error handling flaw can continue AGFL repair after xagb_bitmap_walk fails, leaving the used extent bitmap incomplete. Subsequent repair logic can operate on inconsistent allocation group metadata state and may incorrectly treat live AGFL blocks as unused, which can cause filesystem metadata inconsistency or corruption. For the CVSS the PR:H because triggering the online XFS repair path normally requires filesystem administrative privileges. The issue is local and is not directly network reachable. The base impact is limited integrity and availability impact on the affected filesystem. The paranoid score considers a plausible severe availability impact if an incorrect repair operation makes the affected XFS filesystem unavailable. No memory corruption or privilege escalation primitive is indicated by the patch.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) YES DISK SIMPLEFIX IMPROVEONLY LINUS 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
* Applied score minimum: -1 -> 0. No evidence-supported paranoid signal changes the result.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Important filesystem/storage path. The code is in XFS allocation-group free-list repair, where inconsistent bitmap state can affect filesystem metadata repair decisions.
* -2 Host-admin-equivalent privilege requirement. The affected online XFS scrub and repair operation is an administrative filesystem-management interface and requires CAP_SYS_ADMIN.
* No UAF, stale pointer, OOB access, refcount misuse, double release, or memory-corruption primitive is established.
* No reliable kernel crash, filesystem shutdown, persistent resource exhaustion, or host-wide DoS is demonstrated by the patch.
* No Integrity plausible point is awarded. The patch shows that repair can proceed with incomplete in-memory bitmap data, but does not establish attacker-controlled unauthorized modification of another principals data or a protected filesystem object.
* No Availability point is awarded. Severe filesystem unavailability is a possible downstream operational outcome, but is not demonstrated by the patch context.
* No remote reachability is established.
* No local unprivileged trigger is established.
* No namespace-scoped privilege path is established.
* No controlled reclaim, arbitrary write, information disclosure, privilege escalation, authorization bypass, or ownership/COW violation is demonstrated.
* No manual-review preservation signal applies because this is an unchecked-error logic flaw rather than a concrete kernel corruption primitive.
3. Reachability analysis
The vulnerable path is reached while performing XFS online metadata repair for AGFL state. The supplied patch does not show an ordinary-user syscall path that can independently invoke this repair operation.
The relevant repair interface is administrative and normally requires host CAP_SYS_ADMIN. This is a host-level filesystem-management privilege, not a capability that can be assumed to be usable through an attacker-created namespace for the complete operation.
No prior special hardware, boot option, network exposure, race condition, or attacker-controlled device input is indicated. The triggering condition additionally requires xagb_bitmap_walk to encounter an error from xrep_agfl_fill or xagb_bitmap_set, such as allocation-related bitmap processing failure, while repair is running.
4. Primitive and severity interpretation
The exact defect is unchecked error propagation. xagb_bitmap_walk can fail while building the bitmap of AGFL blocks in use, but the old code ignored that error and continued with incomplete in-memory used_extents state.
This is not an active structured-object UAF and not fixed stale storage. There is no object lifetime violation, no dereference after free, no repeated release or refcount mutation, and no attacker-controlled memory corruption primitive.
The potential consequence is incorrect filesystem metadata repair behavior. In particular, incomplete used_extents tracking could cause later repair logic to reason incorrectly about AGFL blocks. The patch-supported consequence is inconsistent repair state, not a demonstrated arbitrary metadata write, cross-file permission bypass, kernel crash, or privilege escalation.
PrimitiveClass is NONE. ImportantCandidate is NO because the patch does not establish meaningful unresolved exploitation leverage beyond an administrative repair failure. AutoDowngradeAllowed is YES because there is no concrete kernel corruption, authorization bypass, ownership violation, or below-admin attacker path requiring preservation for manual exploitation analysis.
Likely operational severity is low. Systems using XFS online repair should apply the fix in normal maintenance, but the evidence supports deferred handling rather than urgent security remediation.
5. One-sentence report phrase
An XFS online repair error-handling flaw ignored bitmap-walk failures and could continue AGFL repair with incomplete in-memory extent tracking, potentially causing inconsistent filesystem metadata repair state.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The patch establishes an administrative error-handling flaw without a memory-corruption primitive, security-boundary bypass, unprivileged trigger, or demonstrated severe availability consequence.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: xfs: bail out on bitmap errors in xrep_agfl_fill
Commit: e49977bc568c2649cf1a37992e538df8e3779ee4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e49977bc568c2649cf1a37992e538df8e3779ee4
Commit description:
LOLLM also points out that the xagb_bitmap_set call in xrep_agfl_fill
can fail, but we don't check the result of xagb_bitmap_walk, so we
silently drop the error and proceed with inconsistent incore data.
That shouldn't be allowed.
Cc: [email protected] # v6.6
Fixes: 014ad53 ("xfs: use per-AG bitmaps to reap unused AG metadata blocks during repair")
Signed-off-by: Darrick J. Wong <[email protected]>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Carlos Maiolino <[email protected]>
Signed-off-by: Carlos Maiolino <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/xfs/scrub/agheader_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=e49977bc568c2649cf1a37992e538df8e3779ee4
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97542 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97542
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:L/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:H
The Best / paranoid CVSS score: 4.7
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: 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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