[CVE-2026-98174][MODERATE 7.0] smb: client: fix rlist race and missing initialization

[CVE-2026-98174][MODERATE 7.0] smb: client: fix rlist race and missing initialization

[AL-KERNEL]

CVE: CVE-2026-98174
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: smb: client: fix rlist race and missing initialization
Commit: b5f924ffbfa976e4b97f17e8132c595b97482c2d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b5f924ffbfa976e4b97f17e8132c595b97482c2d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98174
Analysis date: Thu, 08 Oct 2026 06:02:22 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
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-2026-98174 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98174

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-2026-98174	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98174 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-362;CWE-665;*CWE-787;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in the SMB client reconnect path can add the same TCP_Server_Info.rlist node to a reconnect list more than once. The rlist node is also not initialized when a TCP session is allocated. Duplicate list insertion can corrupt Linux list metadata and may cause invalid pointer dereferences or a kernel crash during reconnect processing. A remote SMB server or an attacker able to disrupt SMB transport can potentially induce reconnect activity. Reliable triggering requires a timing window between concurrent cifsd threads. For the CVSS the PR:N because no local account or privileges on the client are required when the victim has an SMB client mount connected to an attacker controlled or reachable SMB server. Impact is at least network reachable denial of service via kernel crash. The paranoid assessment includes limited confidentiality and integrity impact because corrupted list metadata is a memory corruption condition. SMB client mounts are commonly used in internal enterprise networks. Practical exploitation normally requires access to the SMB server path or the ability to interfere with the SMB connection.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	MAYBE	LOCK DEADLOCK DISK INIT SIMPLEFIX RACE SERVERTOCLIENT LINUS KPANIC 	-	-	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 4
* Paranoid score: 4
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +1 Constrained kernel list corruption. The same TCP_Server_Info.rlist node can be inserted into a reconnect list more than once, violating list_head membership invariants and corrupting list metadata.
* +2 Remote reachable / directly network-triggerable. A malicious or attacker-controlled SMB server can disrupt the SMB transport and induce client reconnect processing after a victim has mounted the remote share.
* +1 Reliable kernel crash / strong DoS. Corrupted reconnect-list links can cause invalid list traversal or pointer dereference in the SMB client reconnect path.

Important non-awarded signals:

* +0 Real UAF. No object free followed by dereference or second lifetime mutation is established by the patch.
* +0 Controlled reclaim or object replacement. The patch does not show attacker control over reclaimed kernel memory or list pointer values.
* +0 Arbitrary or directed kernel write. List corruption is established, but no attacker-directed write target or payload is demonstrated.
* +0 Structured stale-object leverage. The defect concerns duplicate list membership and list initialization, not stale structured-object processing after replacement.
* +0 Weak LPE concern. Generic theoretical exploitability of corrupted list metadata is insufficient without attacker influence over corrupted links, active replacement, or a useful post-corruption sink.
* +0 Additional Availability impact. The single established effect is a kernel fault or crash and is counted once.
* +0 Confidentiality or Integrity impact. No disclosure, unauthorized modification, controlled overwrite, or privilege-escalation path is established.
* -0 Hard race penalty. The commit establishes concurrent cifsd calls but does not establish a narrow, one-shot, externally uncontrollable timing condition. An attacker controlling SMB transport may repeatedly induce reconnect activity.
* -0 Host-admin privilege penalty. The attacker can act as the remote SMB server and does not require local host administrative privileges after the victim has an SMB client mount.

3. Reachability analysis

The evaluated attacker is a remote SMB server operator, or an attacker able to interfere with the SMB transport to an already mounted SMB share. The attacker can cause connection failures or reconnect-related traffic conditions that reach cifs_signal_cifsd_for_reconnect.

A victim-side SMB client mount is required before the vulnerable reconnect path exists. That mount is a deployment prerequisite, but it is not a privilege requirement for the remote attacker. The supplied patch does not show that the attacker must execute local code, hold CAP_NET_ADMIN, possess host root, or control a network namespace on the victim.

No namespace-scoped capability analysis is relevant to the complete remote trigger. The patch does not require special hardware, a boot parameter, a sysctl, or a nonstandard kernel configuration beyond SMB client use. The concurrency condition is relevant, but repeated transport interruptions can provide repeated opportunities to reach reconnect processing.

4. Primitive and severity interpretation

The exact primitive is duplicate insertion of the same active TCP_Server_Info.rlist list_head into reconnect-list processing, combined with missing list-head initialization for newly allocated TCP sessions. This is kernel list metadata corruption and is classified as CLASS_B because invalid list links can affect later kernel traversal and mutation.

This is not a real UAF based on the supplied patch. The patch does not establish that TCP_Server_Info is freed while a stale reference is dereferenced. It also does not establish a concrete repeated put, release, free, or refcount operation on a potentially freed object.

The demonstrated practical consequence is kernel instability or denial of service during SMB reconnect processing. A more serious consequence would require an additional mechanism not established here, such as attacker control of corrupted list pointers, controlled object replacement, a useful write sink, or a post-corruption callback or type-confusion path.

ImportantCandidate is NO because the supplied evidence supports list corruption and DoS but does not show meaningful attacker control over the resulting corrupted links beyond inducing reconnect races. AutoDowngradeAllowed is YES because the currently established primitive is constrained and crash-oriented, without a demonstrated lifetime violation, controlled corruption, authorization bypass, or reusable exploitation primitive. Manual review remains recommended because the issue is remotely reachable in SMB client deployments and involves corruption of kernel list metadata.

5. One-sentence report phrase

A malicious SMB server can induce concurrent reconnect processing that inserts the same TCP_Server_Info.rlist node more than once, corrupting kernel list metadata and potentially causing a client kernel crash or denial of service.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

The issue is network reachable for systems using SMB client mounts and establishes kernel list corruption, but the supplied patch does not demonstrate controlled pointer corruption, a UAF, information disclosure, integrity impact, or privilege escalation.

7. Call-site confidence

Call-site confidence: medium

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

Patch: smb: client: fix rlist race and missing initialization
Commit: b5f924ffbfa976e4b97f17e8132c595b97482c2d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b5f924ffbfa976e4b97f17e8132c595b97482c2d

Commit description:

TCP_Server_Info.rlist is allocated via kzalloc which zeros both ->next
and ->prev to NULL instead of pointing to itself, making list_empty()
always return false and list_add() dereference a NULL ->prev pointer.

Also, cifs_signal_cifsd_for_reconnect() can be called concurrently
from multiple cifsd threads, allowing the same server's rlist node to
be added twice into the local list, corrupting it.

Closes: https://sashiko.dev/#/patchset/20260911204446.1719356-1-pc%40manguebit.org
Fixes: df0e03a4fb94 ("smb: client: fix potential deadlock when reconnecting channels")
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/smb/client/connect.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=b5f924ffbfa976e4b97f17e8132c595b97482c2d

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

The original Linux kernel CVE announcement for CVE-2026-98174 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98174

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:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 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: 4

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).