[CVE-2026-89972][IMPORTANT] nvme: add missing SRCU grace period in error path

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

CVE: CVE-2026-89972
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: nvme: add missing SRCU grace period in error path
Commit: d663944dbad81bb0e3635d7090db4713e6300858
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d663944dbad81bb0e3635d7090db4713e6300858
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89972
Analysis date: Wed, 16 Sep 2026 08:42:10 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89972 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89972

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
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CVE-2026-89972	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-89972 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-664;*CWE-416;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'A use-after-free can occur in the NVMe host namespace allocation error path because nvme_alloc_ns removes ns from the namespace siblings list with list_del_rcu but frees the namespace without waiting for SRCU readers. Concurrent NVMe multipath readers such as nvme_find_path or nvme_mpath_revalidate_paths can still traverse the namespace head list under srcu_read_lock and keep a stale ns pointer. For the CVSS the PR:N is used for the paranoid score because a malicious or compromised NVMe subsystem or storage endpoint may trigger the faulty error path without requiring a local user account on the victim host. The attack vector is treated as AV:A rather than AV:N because practical exposure is normally limited to an adjacent storage fabric or trusted data center storage network. Impact is at least denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel use-after-free, so this should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	YES	SIMPLEFIX NVME ERRORPATH  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5	NO	NO	checked

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

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 6
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

No floor or cap changed the score.

2. Signal breakdown

Conservative positive signals:

* +2 Real UAF / SRCU lifetime violation. `nvme_alloc_ns()` removes `ns` from the namespace siblings list with `list_del_rcu()` but the error path can free the namespace before SRCU readers finish.
* +1 Concrete SRCU referenced-object lifetime mismatch. Multipath readers traverse the namespace head list under `srcu_read_lock()` in paths such as `nvme_find_path()` and `nvme_mpath_revalidate_paths()`, while the writer failed to wait for the matching SRCU grace period.
* +1 Reliable kernel crash / strong DoS. A concurrent reader can retain and dereference a stale `struct nvme_ns *` after `kfree(ns)`, which realistically supports kernel fault or crash.
* +1 Important storage path. The bug is in NVMe namespace and multipath handling, an active block/storage path where stale namespace state can affect path selection and revalidation.

Paranoid additional signal:

* +1 Adjacent storage endpoint influence. A malicious or compromised NVMe subsystem, controller, or storage endpoint may plausibly influence namespace discovery or allocation failure behavior. This supports adjacent/device-mediated exposure, not Internet-style AV:N reachability.

Non-awarded signals:

* Controlled reclaim is not demonstrated.
* Arbitrary kernel read or write is not demonstrated.
* CLASS_A is not assigned because no controlled replacement, callback control, refcount takeover, or demonstrated privilege escalation is established.
* Concrete repeated release/refcount signal is not awarded. The bug is missing SRCU synchronization before freeing `ns`, not a proven second put/free on the exact same dangling `ns` reference.
* Structured stale-object leverage is not separately awarded because the stale reader behavior is established, but attacker-shaped replacement contents or security-sensitive field consumption after reuse is not shown.
* Confidentiality and integrity points are not separately awarded in ActionableScore because C/I impact remains a worst-case UAF concern, not a demonstrated disclosure or modification primitive.
* Extra Availability is not awarded because the crash/DoS is already counted once.
* Hard race penalty is not applied. The bug is concurrent, but the evidence does not establish a narrow one-shot or externally uncontrollable race sufficient for a negative point.
* Host-admin penalty is not applied because host-admin-equivalent triggering is not positively established.

Repeated-release/refcount checklist:

* First release can end lifetime: not the scored primitive for `ns`.
* Exact same reference survives to second lifetime mutation: not established.
* Second operation is a real lifetime/refcount mutation on the same dangling `ns`: not established.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no. Score reaches 5 by arithmetic.

3. Reachability analysis

The affected path is in NVMe host namespace allocation error handling. The trigger requires `nvme_alloc_ns()` to reach the `out_unlink_ns` style error path after publishing or linking a namespace in a way visible to multipath SRCU readers.

A local ordinary user trigger is not established from the supplied patch. Host-admin-equivalent privilege is also not positively established as a complete requirement, because namespace discovery and controller behavior may be influenced by an external NVMe subsystem or storage endpoint. Therefore `HostAdminRequired=UNKNOWN`.

The most plausible non-local attacker model is a malicious, compromised, or attacker-controlled NVMe storage endpoint already reachable by the host. This is adjacent or device/storage-fabric mediated exposure, not general network reachability. Prior host configuration to use that NVMe subsystem may exist, but the supplied evidence does not fully resolve whether the attacker can cause the complete trigger without such prior setup.

Namespace-scoped privilege is not applicable. There is no evidence that a user or network namespace capability permits the full vulnerable operation.

Race repeatability is unresolved. There is a real SRCU reader/writer lifetime race, but the patch does not show that the race is one-shot, extremely narrow, or impossible to retry. No race penalty is applied.

4. Primitive and severity interpretation

The exact primitive is a real SRCU use-after-free of `struct nvme_ns`. The writer removes the namespace from an RCU/SRCU-protected list and can free it before all SRCU readers that may have observed it are gone.

This is an active structured object, not fixed stale storage. The stale object participates in NVMe multipath lookup and path revalidation. The demonstrated consequence is at least host kernel crash or DoS from stale namespace dereference.

This is not merely ordinary stale cleanup metadata. The missing `synchronize_srcu(&ns->head->srcu)` violates the core lifetime rule for readers traversing `head->list`.

However, the patch does not establish CLASS_A exploitation. There is no demonstrated controlled reclaim, arbitrary write, callback hijack, credential manipulation, or proven privilege escalation. The unresolved concern is that this is a real active-object kernel UAF in an important storage path, with possible adjacent storage-endpoint influence.

PrimitiveClass is CLASS_B. ImportantCandidate is YES because meaningful Important-vs-Moderate review remains unresolved for an active structured SRCU UAF. AutoDowngradeAllowed is NO because automatically closing it as ordinary Moderate would lose a concrete kernel lifetime primitive with unresolved exploitation leverage.

Likely operational severity is Actionable Moderate at minimum, with Strong Important review warranted depending on actual reachability from a malicious NVMe subsystem and the depth of stale `ns` field consumption.

5. One-sentence report phrase

A missing SRCU grace period in the NVMe namespace allocation error path can let multipath readers retain a stale namespace pointer after list_del_rcu and kfree, causing a kernel use-after-free and at least host DoS, with adjacent storage endpoint influence plausible enough to require manual security review.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a real active-object SRCU UAF in NVMe multipath namespace handling, with unresolved adjacent storage-endpoint reachability and unresolved post-lifetime exploitation leverage beyond a simple crash.

7. Call-site confidence

Call-site confidence: high

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

Patch: nvme: add missing SRCU grace period in error path
Commit: d663944dbad81bb0e3635d7090db4713e6300858
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d663944dbad81bb0e3635d7090db4713e6300858

Commit description:

nvme_alloc_ns() error path at out_unlink_ns removes ns from the
namespace head siblings list with list_del_rcu(&ns->siblings) but
does not wait for SRCU readers before freeing the namespace struct.
Multipath code iterates the head->list under srcu_read_lock() in
nvme_find_path() and nvme_mpath_revalidate_paths(), so a concurrent
reader can still hold a reference to ns when kfree(ns) runs.

The normal removal path in nvme_ns_remove() correctly calls
synchronize_srcu(&ns->head->srcu) after list_del_rcu() to wait for
in-progress readers. Add the same grace period in the error path.

Fixes: ed754e5 ("nvme: track shared namespaces")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/nvme/host/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=d663944dbad81bb0e3635d7090db4713e6300858

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

The original Linux kernel CVE announcement for CVE-2026-89972 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89972

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:L/I:L/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: 5
  Paranoid ActionableScore: 6

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).