[CVE-2026-72128][MODERATE 7.0] nvmet: fix refcount leak in nvmet_sq_create()

[CVE-2026-72128][MODERATE 7.0] nvmet: fix refcount leak in nvmet_sq_create()

[AL-KERNEL]

CVE: CVE-2026-72128
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: nvmet: fix refcount leak in nvmet_sq_create()
Commit: 26355295ce21cb046546085c3a81abe68160a784
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=26355295ce21cb046546085c3a81abe68160a784
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72128
Analysis date: Sat, 15 Aug 2026 14:52:37 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
A refcount leak in nvmet_sq_create() allows a host with access to the NVMe target to repeatedly trigger the invalid SQID path and pin controller references, potentially causing resource exhaustion and denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-72128 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72128

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.

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

CVE-2026-72128	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-911;**CWE-400;Other CVSS 'AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '6.5';DESCR 'A reference count leak in nvmet_sq_create can occur because the ctrl reference acquired before nvmet_check_sqid is not released when the sqid validation fails. A host that can reach the NVMe target and issue repeated invalid Create I/O Submission Queue requests may keep controller references pinned and gradually exhaust target resources. For the CVSS the PR:N is used in the paranoid score because an exposed or weakly restricted NVMe target may accept protocol traffic from a reachable host without a local account on the victim. The attack is adjacent network oriented in typical NVMe storage deployments and is not expected to be reachable from the public Internet. Impact is denial of service through resource exhaustion. The patch context does not support UAF, OOB access, information disclosure, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	SIMPLEFIX NVME LEAK ERRORPATH IMPROVEONLY LINUS  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	YES	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
  nvmet_sq_create() is in the NVMe target path. A connected NVMe host can plausibly trigger the invalid SQID error path through protocol requests.
* Real lifetime corruption: +1
  This is a reference lifetime bug. kref_get_unless_zero() takes a ctrl reference, but the failing nvmet_check_sqid() path returned without nvmet_ctrl_put().
* Availability impact realistic: +1
  Repeated triggering can pin controller references and prevent cleanup, causing resource leakage and DoS over time.
* Important filesystem/storage path: +1
  NVMe target is an important storage subsystem.
* Rare / non-default deployed exposure: -1
  nvmet is not exposed by default and generally requires an explicitly configured NVMe target.

Paranoid additional interpretation:

* Reliable / strong DoS concern: +1
  If the target is reachable from an untrusted storage network, repeated invalid queue creation attempts may cause sustained resource retention and operational DoS.

No memory corruption, UAF, OOB access, info leak, or privilege escalation primitive is supported by the patch.

## 3. Reachability analysis

The likely trigger is a host that can connect to an NVMe target and issue an invalid Create I/O Submission Queue request that fails nvmet_check_sqid(). No local account on the victim is required if the NVMe target accepts protocol traffic from that host. In typical deployments, NVMe targets are on isolated storage or data-center networks, not the public Internet.

Namespaces and containers do not materially lower the victim-side privilege requirement unless they provide access to the NVMe target endpoint. The affected path is not default Internet exposure, but it is a protocol-facing storage target path when nvmet is configured.

Call-site confidence: medium. The patch shows the exact error path and cleanup label, but not all transport-specific callers.

## 4. Severity interpretation

This behaves more like an actionable Moderate resource-lifetime issue than an Important memory-corruption vulnerability. The theoretical worst case is sustained DoS through controller reference leaks. The realistic evidence supports resource exhaustion, not confidentiality impact, integrity impact, LPE, arbitrary write, UAF, or object reuse.

Because the issue is protocol reachable in a storage target path, it should not be auto-closed solely as a low-risk leak.

## 5. One-sentence report phrase

A refcount leak in nvmet_sq_create() allows a host with access to the NVMe target to repeatedly trigger the invalid SQID path and pin controller references, potentially causing resource exhaustion and denial of service.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: network-adjacent NVMe target reachability and sustained resource exhaustion make this more actionable than an ordinary local leak, but the patch does not support memory corruption or privilege escalation.

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

Patch: nvmet: fix refcount leak in nvmet_sq_create()
Commit: 26355295ce21cb046546085c3a81abe68160a784
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=26355295ce21cb046546085c3a81abe68160a784

Commit description:

In nvmet_sq_create(), a reference on the ctrl is taken
via kref_get_unless_zero() before calling nvmet_check_sqid().
If nvmet_check_sqid() fails, the function returns the error
directly without releasing the reference, leading to a leak.

Fix this by jumping to the "ctrl_put" label, which already
performs the necessary nvmet_ctrl_put(ctrl). This ensures the
reference is properly released on this error path.

Cc: stable@vger.kernel.org
Fixes: 1eb380c ("nvmet: Introduce nvmet_sq_create() and nvmet_cq_create()")
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/core.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=26355295ce21cb046546085c3a81abe68160a784

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

The original Linux kernel CVE announcement for CVE-2026-72128 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72128

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:L/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: 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).