[CVE-2026-98897][MODERATE REGULAR] ksmbd: don't hold ci->m_lock while waiting for a lease break ack

[CVE-2026-98897][MODERATE REGULAR] ksmbd: don't hold ci->m_lock while waiting for a lease break ack

[AL-KERNEL]

CVE: CVE-2026-98897
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ksmbd: don't hold ci->m_lock while waiting for a lease break ack
Commit: 868c9038ffd4af39766d087f68c8f543a3f66635
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=868c9038ffd4af39766d087f68c8f543a3f66635
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98897
Analysis date: Mon, 26 Oct 2026 23:17:18 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A permitted remote SMB client can induce repeated lease-break lock stalls of up to 35 seconds, degrading ksmbd service without demonstrated memory corruption or host crash.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98897 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98897

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: NO

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

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-98897	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98897 CHECK WITH IMPACT FROM ORIG NN NONE | AEGIS IMPACT MODERATE AEGIS_AS=2 LEGACY=MODERATE RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-667;*CWE-833;**CWE-400;Other CVSS 'AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'ksmbd can wait up to 35 seconds for a lease break acknowledgment while holding ci m_lock for read. A cifs client may respond by closing its deferred handle, but the close path needs ci m_lock for write and cannot perform the operation that wakes the waiter until the timeout releases the lock. For the CVSS the PR:L value reflects that reliable triggering normally requires an authenticated SMB identity with permission to open files and request leases on a configured share. The issue is remotely reachable through SMB but requires a specific cached lease and conflicting open sequence. The demonstrated primitive is an operation stall rather than memory corruption, information disclosure, or privilege escalation. Repetition may degrade SMB availability, but host wide resource exhaustion or a kernel crash is not established. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.3 and the production ActionableScore returned 3 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4. The independent weaker Aegis shadow evaluated CVSS 3.1 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 3)	MAYBE	REMOTE DEADLOCK DANGER DISK NOMEMCHK UAF SKIP  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 3.
* Conservative score: 3; no floor or cap applied.
* Raw paranoid score: 3.
* Paranoid score: 3; no additional technically supported primitive.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +2 Remote reachable: an authenticated SMB client can establish the cached lease and issue the conflicting open that reaches the vulnerable break path.
* +1 Availability impact: `oplock_break()` waits up to 35 seconds while holding `ci->m_lock` read-locked, blocking the close path needing the write lock and materially delaying SMB operations.
* No timing penalty: the lease/deferred-close sequence is specific, but no narrow or unreliable race is shown.
* No corruption points: the patch changes lock scope and pins `oplock_info` references; it shows no OOB access, UAF, stale refcount mutation, or active-state corruption.
* No strong-DoS/crash point: host crash, unbounded resource exhaustion, and host-wide failure are not established.
* No authorization signal: no DENY-to-ALLOW decision or omitted security guard exists.
* NEW52/B5-R and NEW53/B3-PENDING do not apply: there is neither an OOB write nor a shared-backing write.

3. Reachability analysis

The supported attacker is a remote authenticated SMB identity permitted to open files and request leases on an already configured share. This is below host administrator and requires neither host UID 0 nor a namespace capability. Normal server/share provisioning is prior administrative configuration, but not host-admin privilege for each trigger. The sequence requires a cached read-handle lease and conflicting open; it is more involved than ordinary traffic, but repeatability is plausible and no difficult race is proven.

4. Primitive and severity reading

The primitive is a bounded lock-dependency stall: the waiter holds the inode read lock while awaiting an action whose close path requires the corresponding write lock. The timeout eventually resolves the condition. This is CLASS_C availability behavior, not memory or lifetime corruption. Repeated SMB degradation is plausible; kernel panic, persistent exhaustion, confidentiality loss, integrity loss, and privilege escalation are unproven. ImportantCandidate is NO and automatic downgrade is allowed because no material unknown corruption or trust-boundary primitive remains.

5. One-sentence report phrase

A permitted remote SMB client can induce repeated lease-break lock stalls of up to 35 seconds, degrading ksmbd service without demonstrated memory corruption or host crash.

6. Manual review advice

NO MANUAL CHECK NEEDED

The patch and call path establish a bounded synchronization/availability defect with no Important-preserving primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: ksmbd: don't hold ci->m_lock while waiting for a lease break ack
Commit: 868c9038ffd4af39766d087f68c8f543a3f66635
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=868c9038ffd4af39766d087f68c8f543a3f66635

Commit description:

When a cifs.ko client caches a read-handle (RH) lease via deferred close
and a conflicting open arrives, ksmbd breaks the lease and waits for the
acknowledgment in wait_for_break_ack() for up to OPLOCK_WAIT_TIME (35s).
__smb_break_all_levII_oplock() runs that wait while holding ci->m_lock
for read.

cifs.ko reacts to a handle-lease break by closing the deferred handle
rather than sending a lease break acknowledgment. That close path
(close_id_del_oplock() -> opinfo_del()) takes ci->m_lock for write and
is exactly what would wake the waiter, but it blocks on the read lock
held by the waiting thread. The break is then resolved only by the 35s
timeout, so xfstests generic/001 takes ~78s with leases enabled versus
~4s with oplocks only.

Collect the target opinfos (each pinned with a reference) while holding
ci->m_lock, then break them after releasing it, matching how
smb_grant_oplock() already breaks a conflicting lease using only a
reference.  The reference keeps the opinfo (and its conn and lease)
alive across the unlocked window, and a close racing the break is
handled by the existing OPLOCK_CLOSING state check. Apply the same fix
to the parent lease break paths.

Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

[ This tree predates the deferred break machinery.  The 6.18.y
backport of the oplock break UAF fix (applied here as c8279ae )
calls oplock_break() directly while holding ci->m_lock, and its
smb2_oplock_break_conn_get() takes down_read(ci->m_lock) internally,
so the three walks self-nest the read lock and deadlock for up to
OPLOCK_WAIT_TIME (35s) once a writer queues on the inode.  Port the
machinery above so the walks collect the breaks and drain them after
releasing ci->m_lock, matching the 7.2.y shape of the fix. ]

Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Abdifatah Suruur <suruurism@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Changed files:
  fs/smb/server/oplock.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=868c9038ffd4af39766d087f68c8f543a3f66635

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

The original Linux kernel CVE announcement for CVE-2026-98897 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98897

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:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: unknown
  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).