* [CVE-2026-97547][MODERATE 7.0] xfs: fix exchange-range reflink flag clearing issue with INO1_WRITTEN
@ 2026-09-28 22:42 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-28 22:42 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-97547
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: xfs: fix exchange-range reflink flag clearing issue with INO1_WRITTEN
Commit: 56f87ac2b9543be2be529b831666682e6df4bc40
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=56f87ac2b9543be2be529b831666682e6df4bc40
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97547
Analysis date: Mon, 28 Sep 2026 18:42:38 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97547 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97547
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-2026-97547 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-97547 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:L/UI:N/S:U/C:N/I:H/A:H';CWE-682;CWE-693;CWE-284;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L';BEST CVSS score: '6.3';DESCR 'An XFS exchange range operation with XFS_EXCHMAPS_INO1_WRITTEN can incorrectly clear the reflink inode flag even though the inode still owns shared written extents. A later write can then use the normal non reflink path instead of CoW and modify physical blocks that remain shared with another reflink related file, causing persistent cross file data corruption. For the CVSS the PR:L value is used because a local user or process must be able to invoke the exchange operation on suitable XFS files, while full administrative privileges are not necessarily required. AC:H reflects the need for a specific mapping layout, the INO1_WRITTEN optimization, an incorrect reflink flag transition, and a later write to the affected extent. The issue is not directly network reachable. The demonstrated impact is integrity loss and possible loss of availability for affected data. There is no demonstrated kernel memory corruption or direct privilege escalation primitive, but the CoW protection bypass and possible impact across files require manual security review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7) MAYBE DANGER DISK LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=7
ActionableScoreLower=6
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 6
* Conservative score: 6
* Raw paranoid score: 7
* Paranoid score: 7
* No floor or cap was applied.
* Final recommended bucket: **Strong Important candidate**::
2. Signal breakdown
Conservative positive signals:
* +1 Local unprivileged trigger. A local process with suitable file access can invoke the exchange-range operation without host-admin-equivalent privilege.
* +1 Practical exploit chain. Exchange with `XFS_EXCHMAPS_INO1_WRITTEN` can clear the wrong reflink state, after which a write uses the non-reflink path and modifies still-shared blocks.
* +1 Dirty-Pipe-like shared-storage corruption. An authorized write to one file can alter storage still referenced by another reflink-related file. The stronger +2 ownership-bypass form is not awarded because lack of write permission to the second file is not established.
* +1 Integrity impact. Persistent cross-file data corruption is explicitly established.
* +1 Filesystem/storage metadata corruption reachable locally. Incorrect inode reflink state changes subsequent extent-write semantics.
* +1 Important filesystem path. XFS extent ownership, reflink state, and CoW correctness are core persistent-storage integrity mechanisms.
Paranoid-only signal:
* +1 Availability impact. Persistent corruption of important file data can make the affected data or dependent service unavailable. This is distinct from a transient crash, but system-wide filesystem shutdown is not established.
Non-awarded signals:
* No UAF, stale post-lifetime object, OOB access, or kernel-memory corruption is established.
* No arbitrary kernel write, controlled reclaim, callback influence, or privilege escalation is demonstrated.
* The stronger Dirty-Pipe-like ownership/COW violation +2 is withheld because the evidence does not establish that the attacker lacks permission to the second file.
* Confidentiality is not awarded because no protected-data disclosure path exists.
* Reliable kernel crash is not awarded.
* Remote reachability is not established.
* No race penalty is applied. This is a deterministic state sequence, not a narrow timing race.
* No complexity penalty is applied merely because a specific mapping layout and later write are required.
3. Reachability analysis
The evaluated attacker is an ordinary local process with access to suitable files on an XFS filesystem using reflink. The process must submit an exchange-range request with `XFS_EXCHMAPS_INO1_WRITTEN`, create the relevant mixture of shared written extents and skipped hole or unwritten mappings, and later write to the inode whose reflink flag was incorrectly cleared.
The supplied evidence and normal file-ioctl semantics support below-host-admin reachability when the caller has the required file access, so `HostAdminRequired=NO`. No namespace-scoped capability is part of the demonstrated trigger, so `NamespaceScopedPrivilege=NO`.
An XFS filesystem with reflink support is a prerequisite, but no special hardware, boot-only mode, narrow race, or firmware involvement is required. Creating or mounting that filesystem may involve prior administration, but exploitation of an already available affected filesystem does not itself require host administration.
4. Primitive and severity interpretation
The exact primitive is a persistent XFS extent-ownership and CoW-state inconsistency. The inode reflink flag can be removed while the inode still references shared written extents. A subsequent write is therefore semantically misclassified as a private non-reflink write and reaches physical storage that should remain protected by CoW.
This is not stale storage or an object-lifetime UAF. It is broader active use of incorrect persistent metadata by the normal write path. There is no repeated release or refcount operation.
The primitive is `CLASS_B` because a concrete active ownership and mapping invariant is violated and attacker-controlled file writes can cause cross-file corruption, but the stronger permission-bypass requirement for `CLASS_A` protected-file corruption is not proven.
The demonstrated consequence is persistent data corruption between reflink-related files. A cross-user protected-file overwrite, filesystem-wide failure, or privilege escalation remains speculative. Nevertheless, meaningful leverage exists beyond a crash because write data can propagate through incorrectly shared storage.
`ImportantCandidate=YES` because the security significance depends on whether the second file can become independently permissioned or security-sensitive while sharing the affected extent. `AutoDowngradeAllowed=NO` because automatically treating this as ordinary metadata corruption would discard a concrete shared-storage and CoW invariant violation with persistent consequences.
Likely operational severity is Actionable Moderate at minimum, with Strong Important treatment justified pending review of permission checks, ownership transitions, snapshots, backup workflows, and cross-principal reflink use.
5. One-sentence report phrase
An XFS exchange-range operation using XFS_EXCHMAPS_INO1_WRITTEN can incorrectly remove reflink state from an inode that still owns shared extents, allowing later writes to bypass CoW and persistently corrupt another reflink-related file.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Review whether exchange participants or resulting reflink files can have independent ownership or permissions, because that determines whether the demonstrated cross-file corruption becomes a protected-file overwrite and full security-boundary violation.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: xfs: fix exchange-range reflink flag clearing issue with INO1_WRITTEN
Commit: 56f87ac2b9543be2be529b831666682e6df4bc40
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=56f87ac2b9543be2be529b831666682e6df4bc40
Commit description:
When exchanging two full-file ranges, xmi_can_exchange_reflink_flags()
can move the reflink inode flag from the file that currently has it to
the other file, as long as exactly one side is marked. This assumes
that the file contents, and therefore all shared extents, are exchanged.
That assumption is not true when XFS_EXCHMAPS_INO1_WRITTEN is set.
xfs_exchmaps_can_skip_mapping() can skip hole and unwritten mappings
from file1, so an exchange can complete without moving every mapping
that the earlier flag-swap decision accounted for. In that case the
post-operation cleanup can clear the reflink flag from an inode that
still owns shared written extents. Later writes then take the
non-reflink write path and may update blocks that should still have
been protected by CoW, which shows up as data corruption between
reflink-related files.
Fix this by disabling the reflink flag exchange whenever
XFS_EXCHMAPS_INO1_WRITTEN is requested. The contents exchange can still
proceed; the conservative outcome is that both inodes keep the reflink
flag. The regular reflink flag cleanup path can drop the extra flag
later once the inode no longer has shared extents.
Reported-by: Lin Jiapeng (TencentOS Red Team) <[email protected]>
Fixes: 966ceaf ("xfs: create deferred log items for file mapping exchanges")
Cc: [email protected] # v6.10
Reviewed-by: Darrick J. Wong <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Lin Jiapeng <[email protected]>
Signed-off-by: Carlos Maiolino <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/xfs/libxfs/xfs_exchmaps.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=56f87ac2b9543be2be529b831666682e6df4bc40
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97547 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97547
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:L/UI:N/S:U/C:N/I:H/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H
The Best / paranoid CVSS score: 6.3
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: 6
Paranoid ActionableScore: 7
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: YES
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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