[CVE-2026-98682][MODERATE 7.0] smb: client: drain and invalidate before server-side copy/clone

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

CVE: CVE-2026-98682
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: smb: client: drain and invalidate before server-side copy/clone
Commit: dc71660f11ef2fecc0695a41e49cd496a9d255ab
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dc71660f11ef2fecc0695a41e49cd496a9d255ab
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98682
Analysis date: Mon, 19 Oct 2026 00:41:38 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: NO

Summary:
A race between SMB server-side copy or clone operations and outstanding destination writeback can restore stale cached data after the server operation and persistently corrupt the destination file for an ordinary user with access to the affected SMB mount.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98682 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98682

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: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-98682	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98682 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=1 LEGACY=MODERATE_KPANIC RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE_KPANIC, Aegis: 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-362;CWE-662;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N';BEST CVSS score: '6.3';DESCR 'The SMB client does not fully serialize server-side copy or clone operations against asynchronous writeback and cached pages for the destination file. An in-flight destination write can complete after the server has copied or cloned the requested range and can restore stale cached data over the new server-side contents. This produces persistent destination file corruption and was observed during generic/363 testing against Windows Server. For the CVSS the PR:L because a local user or process with access to the SMB mount and permission to copy or clone into the destination can reach the affected paths without administrative capabilities. AC:H applies because successful triggering depends on a timing window between asynchronous destination I/O and the server-side operation. The issue is not directly reachable through unsolicited network traffic because the vulnerable operation is initiated on the SMB client, although the affected file and copy operation involve a remote SMB server. The confirmed impact is integrity loss through file corruption. There is no supported kernel memory corruption or information disclosure primitive. The worst still defensible availability impact is loss of access to corrupted application data rather than a kernel crash or privilege escalation. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 6.3 and the production ActionableScore returned 5 with recommendation Actionable Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 1 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5)	MAYBE	READ OOB LOCK DANGER DISK SERVERTOCLIENT LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap was applied.
* Final recommended bucket: **Actionable Moderate**::

2. Signal breakdown

Conservative positive signals:

* +1 Local unprivileged trigger. A user with ordinary access to an SMB mount and write permission for the destination can invoke copy or clone without host-administrator capabilities.
* +1 Active-state synchronization violation. Live destination page-cache and netfs write state remains operational while a server-side replacement is performed without holding `invalidate_lock` or draining outstanding I/O.
* +1 Concrete persistent data corruption. A late asynchronous write can restore stale data over the range already copied or cloned by the server. This was observed by `generic/363`.
* +1 Important filesystem and storage path. The defect affects SMB copy offload, page-cache invalidation, writeback ordering, and persistent file contents.

Paranoid additional signal:

* +1 Availability consequence. Persistent corruption can make the affected destination data unusable and can disrupt an application relying on that file. This is distinct from a kernel crash, which is not established.

Non-awarded signals:

* +0 Remote reachability. The SMB server is remote, but the vulnerable operation is initiated through a local client filesystem operation rather than unsolicited network traffic.
* +0 Hard-race penalty. The issue is timing-dependent, but it occurred under filesystem testing and the supplied evidence does not establish a narrow, one-shot, or externally uncontrollable race.
* +0 Cross-user or COW ownership violation. The patch establishes corruption of the selected destination file, not modification of an independently permissioned file.
* +0 Authorization bypass. No DENY-to-ALLOW security decision is changed.
* +0 Kernel memory corruption, UAF, OOB write, arbitrary write, disclosure, or privilege escalation. None is established.
* +0 B3-PENDING, B4-PENDING, B5-R, V32, V33, and V34. The required shared-backing authority violation, authorization bypass, heap OOB write, checksum metadata corruption, or privileged downstream trust-boundary chain is absent.

3. Reachability analysis

An ordinary local process can invoke `copy_file_range`, the SMB copychunk path, or `FICLONE` when it has suitable access to the source and destination files on an existing CIFS mount. The same process can generate destination writes or memory-mapped dirty data whose asynchronous completion races with the server-side operation.

No host UID 0, host capability, namespace capability, special hardware, boot option, or device-management privilege is required for these file operations. A previously mounted SMB share and a server supporting the relevant server-side copy or clone operation are prerequisites, but that deployment setup does not make every subsequent trigger host-admin-only.

The race is local to the SMB client page-cache and writeback ordering. A malicious SMB server is not required by the demonstrated scenario. The issue was observed against Windows Server, but unsolicited server traffic alone is not shown to trigger it.

4. Primitive and severity interpretation

The exact primitive is a synchronization failure between active destination writeback and a server-side copy or clone. The destination page cache is invalidated without retaining the invalidation lock across the server ioctl, and outstanding netfs writes are not drained. A stale in-flight write can therefore complete after the server operation and persistently overwrite the newly copied range.

This is active filesystem state rather than fixed stale storage, but it is not a post-lifetime object use. There is no concrete repeated release, refcount mutation, UAF, kernel heap overwrite, or active-object replacement.

`CLASS_B` is appropriate because a concrete active-state consistency violation produces persistent file-data corruption beyond a warning or crash-only condition. The demonstrated consequence is corruption of the destination selected by the caller. A broader protected-file overwrite, cross-user authorization bypass, kernel compromise, or privilege escalation remains unsupported.

`ImportantCandidate=NO` because no protected victim, cross-authority ownership violation, or kernel corruption primitive is established. `AutoDowngradeAllowed=YES` because the confirmed primitive is constrained to operation-ordering corruption of an authorized destination and no unresolved Important-preserving boundary primitive is present. The operational severity is Actionable Moderate because persistent storage corruption is concrete and should not be treated as a harmless warning.

5. One-sentence report phrase

A race between SMB server-side copy or clone operations and outstanding destination writeback can restore stale cached data after the server operation and persistently corrupt the destination file for an ordinary user with access to the affected SMB mount.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether any call path can copy into a destination outside the callers normal write authority or can convert clone or shared-backing behavior into cross-file corruption. The supplied evidence establishes same-destination corruption but not an Important-grade ownership or authorization bypass.

7. Call-site confidence

Call-site confidence: high

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

Patch: smb: client: drain and invalidate before server-side copy/clone
Commit: dc71660f11ef2fecc0695a41e49cd496a9d255ab
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dc71660f11ef2fecc0695a41e49cd496a9d255ab

Commit description:

cifs_file_copychunk_range() and the clone (FICLONE) path of
cifs_remap_file_range() do not serialise the destination page cache
against the server-side copy the way the other server-side range
operations (smb3_zero_range(), smb3_punch_hole(), smb3_collapse_range()
and smb3_insert_range()) do.

cifs_file_copychunk_range() invalidates the destination range with
filemap_invalidate_inode(), which takes and drops the mapping's
invalidate_lock internally, so the lock is no longer held when the
copychunk ioctl is issued.  It also never drains in-flight netfs I/O on
the target.  The clone path never takes the invalidate_lock at all (only
i_rwsem), uses a bare truncate_inode_pages_range() and likewise does not
drain outstanding I/O.

As a result an asynchronous destination writeback can complete after the
server-side copy/clone has run and reinstate stale data over the region
just written by the server, corrupting the file.  This is the same class
of corruption as commit d7d2adc ("smb/client: flush dirty data
before punching a hole") and has been seen randomly in generic/363
against Windows Server.

Fix both paths to follow the established ordering: hold the target
mapping's invalidate_lock across the flush and invalidation of the
destination and the server ioctl, and call netfs_wait_for_outstanding_io()
on the target to drain in-flight writes before the ioctl is issued.  Only
the target inode's invalidate_lock is required, as the source is merely
flushed and not invalidated; i_rwsem (already held via
lock_two_nondirectories()) is acquired before the invalidate_lock,
matching the VFS lock ordering.  Since filemap_invalidate_inode() takes
that same lock internally, replace it with its own unmap/flush/invalidate
steps instead of calling it, and return early on a zero-length copy to
avoid a range underflow.

Fixes: 8101d6e ("cifs: Fix copy offload to flush destination region")
Fixes: c54fc3a ("cifs: Fix flushing, invalidation and file size with FICLONE")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/smb/client/cifsfs.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=dc71660f11ef2fecc0695a41e49cd496a9d255ab

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

The original Linux kernel CVE announcement for CVE-2026-98682 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98682

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:N
  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: 4
  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: 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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).