[CVE-2026-46135][IMPORTANT] nvmet-tcp: fix race between ICReq handling and queue teardown

[CVE-2026-46135][IMPORTANT] nvmet-tcp: fix race between ICReq handling and queue teardown

[AL-KERNEL]

CVE: CVE-2026-46135
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: nvmet-tcp: fix race between ICReq handling and queue teardown
Commit: 49891c8fe0cb43fbbe480da1cdccfbbaeb820cb3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=49891c8fe0cb43fbbe480da1cdccfbbaeb820cb3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46135
Analysis date: Thu, 28 May 2026 13:16:48 -0400
ActionableScore: 8
ActionableScore lower bound: 7
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in the NVMe/TCP target ICReq path can let a remote host close the connection during queue teardown and cause a second `kref_put()` on an already released queue, leading to DoS and possible lifetime corruption.

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

The original Linux kernel CVE announcement for CVE-2026-46135 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46135

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: IMPORTANT
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
======================================================================

CVE-2026-46135	IMPORTANT	CHECK	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-362;*CWE-416;CWE-415;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 NVMe TCP target can occur when a host sends ICReq and immediately closes the connection while target side queue teardown is already moving the queue to DISCONNECTING. Later io_work can process the buffered ICReq and overwrite the queue state back to LIVE or FAILED, which can bypass the teardown guard and allow a second kref_put() on an already released queue. For the CVSS the PR:N is used because a remote NVMe TCP host can trigger the ICReq close race when the target listener is reachable, without a local account on the target. AC:H is kept because reliable triggering depends on a teardown timing window. Impact is at least denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact due to queue lifetime corruption. NVMe TCP targets are usually deployed on isolated storage or data center networks, so AV:A is used instead of broad Internet AV:N.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) 	MAYBE	REMOTE LOCK DANGER INIT NVME RACE NETWORK LINUS KPANIC  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=7

## 1. ActionableScore

* Conservative score: **7**
* Paranoid score: **8**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Remote reachable / network-triggerable: **+2**. A remote NVMe/TCP host can send `ICReq` and close the connection when the target listener is reachable.
* Strong memory corruption primitive: **+2**. The commit explicitly describes a second `kref_put()` on an already released queue, which is a lifetime corruption / double-release candidate.
* Real lifetime corruption: **+1**. This is a queue lifetime bug involving teardown, state rollback, and reference dropping after release.
* Weak to moderate LPE concern: **+1**. A double `kref_put()` / released queue path can become UAF-like, but the patch does not show a controlled reclaim or overwrite primitive.
* Reliable kernel crash / strong DoS: **+1**. The realistic immediate impact is target kernel crash or service disruption.
* Availability impact realistic: **+1**. NVMe/TCP target failure can affect storage availability.
* Important filesystem/storage path: **+1**. NVMe/TCP target is a storage transport path.
* Hard race / timing required: **-1**. Reliable triggering depends on timing between ICReq processing, connection close, softirq teardown, and later `io_work`.
* Configuration-dependent exposure: **-1 conservative only**. NVMe/TCP target must be enabled and reachable. This is not a default Internet-facing service in most deployments.

## 3. Reachability analysis

The bug is reachable by a remote NVMe/TCP host that can connect to the target and race ICReq handling with immediate connection teardown. No local account on the target is required if the NVMe/TCP listener is reachable. The practical exposure is usually adjacent or internal storage networks rather than the public Internet. Containers and namespaces are less relevant on the target side, but any workload or host with network access to the NVMe/TCP target could potentially trigger the race. Exploitation reliability is timing-dependent, but the described sequence is realistic for a network client.

## 4. Severity interpretation

This behaves like a **Strong Important candidate**. The conservative interpretation is remote-adjacent DoS through a queue teardown race. The paranoid interpretation is stronger because the commit explicitly describes a second `kref_put()` on an already released queue, which is a lifetime corruption primitive and may become UAF-like. There is no demonstrated privilege escalation or controlled object reuse in the patch, so it should not be treated as proven code execution, but it is too strong to auto-close as ordinary Moderate.

## 5. One-sentence report phrase

A race in the NVMe/TCP target ICReq path can let a remote host close the connection during queue teardown and cause a second `kref_put()` on an already released queue, leading to DoS and possible lifetime corruption.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Manual review is required because this is a network-reachable storage target race with explicit released-queue reference misuse, making UAF or double-free style impact plausible even though exploitation beyond DoS is not demonstrated.

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

Patch: nvmet-tcp: fix race between ICReq handling and queue teardown
Commit: 49891c8fe0cb43fbbe480da1cdccfbbaeb820cb3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=49891c8fe0cb43fbbe480da1cdccfbbaeb820cb3

Commit description:

nvmet_tcp_handle_icreq() updates queue->state after sending an
Initialization Connection Response (ICResp), but it does so without
serializing against target-side queue teardown.

If an NVMe/TCP host sends an Initialization Connection Request
(ICReq) and immediately closes the connection, target-side teardown
may start in softirq context before io_work drains the already
buffered ICReq. In that case, nvmet_tcp_schedule_release_queue()
sets queue->state to NVMET_TCP_Q_DISCONNECTING and drops the queue
reference under state_lock.

If io_work later processes that ICReq, nvmet_tcp_handle_icreq() can
still overwrite the state back to NVMET_TCP_Q_LIVE. That defeats the
DISCONNECTING-state guard in nvmet_tcp_schedule_release_queue() and
allows a later socket state change to re-enter teardown and issue a
second kref_put() on an already released queue.

The ICResp send failure path has the same problem. If teardown has
already moved the queue to DISCONNECTING, a send error can still
overwrite the state with NVMET_TCP_Q_FAILED, again reopening the
window for a second teardown path to drop the queue reference.

Fix this by serializing both post-send state transitions with
state_lock and bailing out if teardown has already started.

Use -ESHUTDOWN as an internal sentinel for that bail-out path rather
than propagating it as a transport error like -ECONNRESET. Keep
nvmet_tcp_socket_error() setting rcv_state to NVMET_TCP_RECV_ERR before
honoring that sentinel so receive-side parsing stays quiesced until the
existing release path completes.

Fixes: c46a6465bac2 ("nvmet-tcp: add NVMe over TCP target driver")
Cc: stable@vger.kernel.org
Reported-by: Shivam Kumar <skumar47@syr.edu>
Tested-by: Shivam Kumar <kumar.shivam43666@gmail.com>
Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/nvme/target/tcp.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=49891c8fe0cb43fbbe480da1cdccfbbaeb820cb3

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

The original Linux kernel CVE announcement for CVE-2026-46135 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46135

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: 7
  Paranoid ActionableScore: 8

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).