[CVE-2026-46027][MODERATE REGULAR] net/smc: avoid early lgr access in smc_clc_wait_msg

[CVE-2026-46027][MODERATE REGULAR] net/smc: avoid early lgr access in smc_clc_wait_msg

[AL-KERNEL]

CVE: CVE-2026-46027
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/smc: avoid early lgr access in smc_clc_wait_msg
Commit: f0858e1d5624bb120b198f2a8528f97a9b0ae069
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f0858e1d5624bb120b198f2a8528f97a9b0ae069
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46027
Analysis date: Wed, 27 May 2026 16:15:44 -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-2026-46027 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46027

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: YES

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

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

CVE-2026-46027	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-476;*CWE-20;CWE-703;BEST CVSS score: '7.5';DESCR 'SMC CLC decline handling can access link group state before the connection is associated with a link group. A remote SMC peer can send an early first contact decline during handshake and make smc_clc_wait_msg() dereference a NULL lgr pointer, causing a kernel crash or connection handling DoS. For the CVSS the PR:N is used because no local privileges are required on the victim when an SMC endpoint is reachable. The issue is network reachable for systems using SMC, but exposure depends on SMC being enabled and reachable by the attacker. Impact is denial of service only, with no supported information disclosure or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4) 	MAYBE	SIMPLEFIX LINUS  INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=4

1. ActionableScore
* Conservative score: 4
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**::

2. Signal breakdown
* Remote reachable / network-triggerable: +2. A remote SMC peer can send an early CLC decline during handshake when the SMC endpoint is reachable.
* Reliable kernel crash / strong DoS: +1. The bug can dereference `smc->conn.lgr` before it exists, causing NULL pointer dereference and DoS.
* Availability impact realistic: +1. The realistic impact is connection handling failure or kernel crash.
* Rare/configuration-dependent exposure: -1. SMC must be enabled and reachable, and this is not a generic TCP/IP core path.
* Weak corruption only: +0. This is a NULL pointer dereference, not UAF, OOB write, arbitrary write, or a demonstrated memory corruption primitive.
* No C/I impact. No information disclosure, integrity corruption, or privilege escalation path is supported by the patch context.

3. Reachability analysis
The bug is reachable from a peer that can initiate or participate in an SMC handshake and send a first-contact CLC decline before link-group setup completes. No local privileges are needed on the victim once SMC is exposed. Namespaces do not materially change the remote attack model. Practical exposure depends on whether SMC is enabled, configured, and reachable in the deployment.

4. Severity interpretation
This behaves like a network-reachable DoS issue, not an Important-class memory-corruption vulnerability. The theoretical impact is limited because the primitive is a NULL pointer dereference of missing link-group state. Realistic exploitation is a crash or service disruption on SMC-enabled systems, with no evidence of LPE, info leak, or arbitrary write.

5. One-sentence report phrase
A remote SMC peer can send an early first-contact CLC decline before link-group setup and trigger a NULL `lgr` dereference in `smc_clc_wait_msg()`, causing network-reachable DoS on SMC-enabled systems.

6. Manual review recommendation
MANUAL CHECK RECOMMENDED. The bug is network reachable in SMC deployments, but it is a NULL pointer dereference only and does not show memory corruption or privilege escalation.

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

Patch: net/smc: avoid early lgr access in smc_clc_wait_msg
Commit: f0858e1d5624bb120b198f2a8528f97a9b0ae069
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f0858e1d5624bb120b198f2a8528f97a9b0ae069

Commit description:

A CLC decline can be received while the handshake is still in an early
stage, before the connection has been associated with a link group.

The decline handling in smc_clc_wait_msg() updates link-group level sync
state for first-contact declines, but that state only exists after link
group setup has completed. Guard the link-group update accordingly and
keep the per-socket peer diagnosis handling unchanged.

This preserves the existing sync_err handling for established link-group
contexts and avoids touching link-group state before it is available.

Fixes: 0cfdd8f ("smc: connection and link group creation")
Cc: stable@kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Signed-off-by: Ruijie Li <ruijieli51@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Link: https://patch.msgid.link/08c68a5c817acf198cce63d22517e232e8d60718.1776850759.git.ruijieli51@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/smc/smc_clc.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=f0858e1d5624bb120b198f2a8528f97a9b0ae069

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

The original Linux kernel CVE announcement for CVE-2026-46027 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46027

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: Not available
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 7.5

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: 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).