[CVE-2026-64541][MODERATE 7.0] net/smc: fix UAF in smc_cdc_rx_handler() by pinning the socket [ Upstream

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

CVE: CVE-2026-64541
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/smc: fix UAF in smc_cdc_rx_handler() by pinning the socket [ Upstream
Commit: 8de4f665d0febfb92803dece377791a563fc7041
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8de4f665d0febfb92803dece377791a563fc7041
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64541
Analysis date: Mon, 27 Jul 2026 22:18:55 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in the SMC-R CDC receive handler can leave `smc_cdc_rx_handler()` using an `smc_sock` after concurrent connection teardown frees it, causing a network-adjacent UAF that can panic the kernel and requires manual review for possible memory-corruption impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64541 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64541

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-64541	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A race in the SMC-R CDC receive path can cause a use after free because smc_cdc_rx_handler looks up a connection under conns_lock, drops the lock, and then uses the derived smc_sock without holding a socket reference. A concurrent close path can unregister the connection and drop the last socket reference before the handler later calls sock_hold, so the handler may operate on freed memory. For the CVSS the PR:N because a peer on the SMC-R capable RDMA fabric can send CDC traffic without local privileges on the victim, but reliable triggering still depends on racing receive processing with connection teardown. The issue is network adjacent rather than generally Internet reachable because SMC-R depends on RDMA capable deployments. Impact is at least denial of service via warning or kernel panic and in the paranoid case may allow confidentiality or integrity impact because the primitive is a real UAF on a socket related object.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)	YES	LOCK UAF  INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote or network-adjacent trigger: +2. SMC-R CDC traffic is received from a peer over an RDMA-capable fabric, so this is not purely local, but it is not generally Internet-reachable.
* Memory corruption, weak primitive: +1. The patch and commit describe a real UAF, but it is race-dependent and no controlled reclaim, stale callback, type confusion, or write-after-free primitive is shown.
* Real lifetime corruption: +1. The bug is specifically a missing socket reference across `conns_lock` release.
* Reliable kernel crash / strong DoS: +1. The report shows refcount warning and kernel panic with `panic_on_warn`.
* Hard or unreliable race: -1. Triggering requires racing CDC receive handling with concurrent connection teardown.
* Rare / configuration-dependent exposure: -1. Only SMC-R is affected, requiring SMC over RDMA deployment.

Conservative total: 3.

Paranoid adjustment:

* Keep the same bug class as race-dependent UAF.
* Do not upgrade to strong LPE primitive because no attacker-controlled reclaim or overwrite is shown.
* Raise to 5 for manual-review sensitivity because this is a network-adjacent lifetime UAF in a socket/network receive path with a demonstrated panic and plausible but unproven memory-corruption consequences.

## 3. Reachability analysis

The bug can be triggered by an SMC-R peer that can send CDC messages while the local endpoint is concurrently closing and unregistering the connection. No local privileges on the victim are required for the peer side, but practical triggering requires access to an SMC-R capable RDMA fabric and a timing window during connection teardown.

Namespaces and containers do not appear to be the main reachability factor. The important boundary is RDMA or SMC-R network adjacency. SMC-R is not a default Internet-exposed protocol in typical deployments and is more common in controlled data-center or specialized environments.

Call-site confidence: high. The patch directly shows the lookup, lock release, socket reference acquisition, and new `sock_hold()` / `sock_put()` lifetime fix in the affected receive handler.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it is a real UAF in a network receive path and has demonstrated kernel panic potential. It is not automatically a full Important-class LPE because the patch does not show controlled object reuse, attacker-controlled reclaim, type confusion, callback control, or an arbitrary write primitive.

Realistically, the demonstrated impact is DoS. Theoretical memory-corruption impact is plausible enough to require manual review, but not strong enough to score as a confirmed privilege escalation.

## 5. One-sentence report phrase

A race in the SMC-R CDC receive handler can leave `smc_cdc_rx_handler()` using an `smc_sock` after concurrent connection teardown frees it, causing a network-adjacent UAF that can panic the kernel and requires manual review for possible memory-corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a race-based UAF in a network-adjacent receive path with demonstrated crash behavior. Even though the conservative evidence supports DoS more than LPE, the lifetime primitive is serious enough that it should not be auto-closed.

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

Patch: net/smc: fix UAF in smc_cdc_rx_handler() by pinning the socket [ Upstream
Commit: 8de4f665d0febfb92803dece377791a563fc7041
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8de4f665d0febfb92803dece377791a563fc7041

Changed files:
  lib/refcount.c
  net/smc/smc_cdc.c
  net/smc/smc_wr.c
  kernel/softirq.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=8de4f665d0febfb92803dece377791a563fc7041

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

The original Linux kernel CVE announcement for CVE-2026-64541 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64541

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:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/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: 3
  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: NO
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).