[CVE-2026-64321][MODERATE 7.0] nvme: target: rdma: fix ndev refcount leak on queue connect

[CVE-2026-64321][MODERATE 7.0] nvme: target: rdma: fix ndev refcount leak on queue connect

[AL-KERNEL]

CVE: CVE-2026-64321
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: nvme: target: rdma: fix ndev refcount leak on queue connect
Commit: d65fe42820b890a6a4644de0a95a812471f79ad3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d65fe42820b890a6a4644de0a95a812471f79ad3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64321
Analysis date: Sat, 25 Jul 2026 06:00:51 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: NO

Summary:
An NVMe/RDMA target can leak an ndev reference when the queue connect backlog is exceeded, allowing a fabric-reachable host to repeatedly trigger resource retention and potential denial of service without requiring local privileges on the target.

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

The original Linux kernel CVE announcement for CVE-2026-64321 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64321

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: NO

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-2026-64321	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-772;*CWE-401;CWE-404;**CWE-400;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '6.5';DESCR 'An ndev reference leak in the NVMe/RDMA target connect path can occur when nvmet_rdma_queue_connect gets an ndev reference and then returns NVME_SC_CONNECT_CTRL_BUSY because the host queue backlog is exceeded. A remote RDMA host that can reach the NVMe/RDMA target may repeatedly drive this failure path and keep leaking references, which can prevent normal device teardown or resource reclamation and may lead to denial of service. For the CVSS the PR:N is used in the paranoid score because the trigger is a remote fabric connect attempt and does not require a local user account on the target. The issue is adjacent network reachable rather than Internet reachable in typical deployments because NVMe/RDMA is usually limited to trusted storage or data center fabrics. Impact is availability only unless further evidence shows memory corruption or a stale pointer traversal primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	LOCK SIMPLEFIX NVME LEAK LOG LINUS  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	YES	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Remote reachable / network-triggerable: +2
  The vulnerable path is in NVMe/RDMA target queue connection handling and can be reached by an RDMA host that can connect to the target fabric.

* Real lifetime corruption: +1
  The bug leaks an ndev kref acquired by nvmet_rdma_find_get_device(), so this is a real reference lifetime bug, but it is a leak rather than UAF or double-free.

* Reliable availability impact: +1
  Repeated connect attempts that hit the backlog-exceeded path can accumulate leaked references and may prevent device teardown or resource reclamation.

* Important filesystem/storage path: +1
  The affected code is in the NVMe target RDMA storage transport path.

* Rare / non-default deployment: -1
  NVMe/RDMA targets require RDMA-capable infrastructure and are typically deployed in storage fabrics or data-center networks, not broadly exposed by default.

No memory corruption, LPE, confidentiality, integrity, Dirty-Pipe-like, page-cache, or arbitrary-write signal is supported by the patch.

## 3. Reachability analysis

A remote RDMA initiator that can reach the NVMe/RDMA target can trigger the affected connect path. No local account on the target is required, so PR:N is reasonable for CVSS-style modeling when the RDMA fabric is reachable. In practice, exposure is usually limited to trusted storage networks, and the bug requires the queue backlog failure path to be hit repeatedly. Namespaces and containers are not the main factor here because the trigger is a fabric-level target connection attempt, not a local syscall-only interface.

Call-site confidence: high, because the patch and commit message explicitly identify nvmet_rdma_queue_connect(), nvmet_rdma_find_get_device(), kref_get(), the backlog branch, and the missing put_device path.

## 4. Severity interpretation

This behaves like an actionable Moderate resource-lifetime issue, not a classic Important memory-corruption vulnerability. The realistic impact is availability loss through reference leaks and possible blocked teardown or resource exhaustion. There is no evidence of UAF reuse, stale pointer traversal, attacker-controlled reclaim, arbitrary write, confidentiality impact, or privilege escalation. The paranoid score reaches 5 because the issue is fabric-network reachable and can be repeatedly triggered against a storage target.

## 5. One-sentence report phrase

An NVMe/RDMA target can leak an ndev reference when the queue connect backlog is exceeded, allowing a fabric-reachable host to repeatedly trigger resource retention and potential denial of service without requiring local privileges on the target.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because the issue is reachable over an RDMA storage fabric and deployment exposure determines practical severity, but the patch supports resource leak and DoS only, not memory corruption or privilege escalation.

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

Patch: nvme: target: rdma: fix ndev refcount leak on queue connect
Commit: d65fe42820b890a6a4644de0a95a812471f79ad3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d65fe42820b890a6a4644de0a95a812471f79ad3

Commit description:

nvmet_rdma_queue_connect() calls nvmet_rdma_find_get_device() which
acquires a reference on the returned ndev via kref_get(). On the path
where the host queue backlog is exceeded and the function returns
NVME_SC_CONNECT_CTRL_BUSY, reference of ndev is not released, leaking
the kref.

Fix this by adding a goto to the existing put_device label before the
early return.

Fixes: 31deaeb ("nvmet-rdma: avoid circular locking dependency on install_queue()")
Cc: stable@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/nvme/target/rdma.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=d65fe42820b890a6a4644de0a95a812471f79ad3

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

The original Linux kernel CVE announcement for CVE-2026-64321 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64321

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:L/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 6.5

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).