[CVE-2026-64048][MODERATE 7.0] net/smc: reject CHID-0 ACCEPT that matches an empty ism_dev slot [ Upstream

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

CVE: CVE-2026-64048
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net/smc: reject CHID-0 ACCEPT that matches an empty ism_dev slot [ Upstream
Commit: 6927cacf2b10d4fa80c1a2d407512ef9397c59c6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6927cacf2b10d4fa80c1a2d407512ef9397c59c6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64048
Analysis date: Sun, 19 Jul 2026 20:09:36 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious SMC-Dv2 peer can reply with CHID 0 and cause the client to select an empty ISM device slot, leading to a NULL pointer dereference in `smc_conn_create()` and a network-triggerable kernel crash.

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

The original Linux kernel CVE announcement for CVE-2026-64048 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64048

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-2026-64048	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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-754;BEST CVSS score: '7.5';DESCR 'A NULL pointer dereference in the SMC-D client CHID selection path can occur because CHID 0 from a peer can match the empty reserved slot 0 when no SMC-Dv1 device is selected. A malicious SMC peer can reply to an SMC-Dv2 only proposal with CHID 0, causing the client to select a NULL ISM device and later dereference lgr_lock during connection setup. For the CVSS the PR:N is used because the attacker only needs to control the peer endpoint or traffic seen by the SMC client, not a local account on the victim. The issue is network reachable in deployments where SMC-D or SMC-Dv2 negotiation is enabled and a client connects to an attacker controlled peer. Impact is denial of service only because the primitive shown by the code is a NULL pointer dereference, not UAF or controllable memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	KASAN NULLPTR HARDWARE  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. A malicious SMC peer can send an ACCEPT with CHID 0 during SMC-Dv2 negotiation.
* Reliable kernel crash / strong DoS: +1. The described path reaches `ism_dev[0]->lgr_lock` with `ism_dev[0] == NULL`, causing a NULL pointer dereference.
* Availability impact realistic: +1. The effect is a host kernel crash during connection setup, not merely a warning.
* Practical exploit chain demonstrated or strongly implied: +1. The commit describes the exact malicious peer response and call path to the fault.
* Rare AND difficult-to-reach subsystem/configuration: -1. Practical exposure depends on SMC-D/SMC-Dv2 support and relevant deployment conditions.

Paranoid difference:

* In environments where SMC-Dv2 is enabled and used, the rare-configuration penalty may be removed, giving score 5.

Not counted:

* Generic memory corruption: +0. The demonstrated primitive is NULL pointer dereference, not UAF, OOB write, type confusion, or controllable overwrite.
* Privilege escalation plausible: +0. No reclaim, write primitive, callback control, or object replacement is shown.
* Confidentiality / integrity impact: +0. The patch supports DoS only.

## 3. Reachability analysis

The bug can be triggered by a malicious peer participating in SMC-Dv2 negotiation with an affected client. The attacker does not need a local account on the victim if they can act as the peer endpoint or otherwise influence the negotiation traffic. Namespaces and containers are not the main factor here because the vulnerable action is on the client connection path. Realistic exploitation requires that SMC-D/SMC-Dv2 is available and negotiated, so exposure is narrower than common TCP/IP packet processing but still network-reachable in affected deployments.

Call-site confidence: high. The commit provides the direct caller chain from `smc_v2_determine_accepted_chid()` to `smc_conn_create()` and the concrete NULL dereference site.

## 4. Severity interpretation

This behaves like an actionable Moderate network-reachable DoS, not an Important-class memory corruption issue. The theoretical impact is limited by the primitive: selecting an empty slot causes a NULL pointer dereference at a fixed low offset. There is no evidence of attacker-controlled memory corruption, UAF reuse, information disclosure, or privilege escalation. However, because the crash is remotely triggerable by a malicious peer in affected SMC-Dv2 deployments, it should not be auto-closed as an ordinary low-priority correctness fix.

## 5. One-sentence report phrase

A malicious SMC-Dv2 peer can reply with CHID 0 and cause the client to select an empty ISM device slot, leading to a NULL pointer dereference in `smc_conn_create()` and a network-triggerable kernel crash.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: network-reachable kernel crash with a clear malicious peer trigger, even though the demonstrated primitive is DoS-only and does not support LPE or memory corruption escalation.

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

Patch: net/smc: reject CHID-0 ACCEPT that matches an empty ism_dev slot [ Upstream
Commit: 6927cacf2b10d4fa80c1a2d407512ef9397c59c6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6927cacf2b10d4fa80c1a2d407512ef9397c59c6

Changed files:
  net/smc/smc_core.c
  net/smc/af_smc.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=6927cacf2b10d4fa80c1a2d407512ef9397c59c6

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

The original Linux kernel CVE announcement for CVE-2026-64048 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64048

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: 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).