[CVE-2026-98815][MODERATE 7.0] nvme: fix cdev lifetime [ Upstream

[CVE-2026-98815][MODERATE 7.0] nvme: fix cdev lifetime [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98815
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: nvme: fix cdev lifetime [ Upstream
Commit: 98b09ad7934482e64db4b4477d91e3bbf43adf4c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=98b09ad7934482e64db4b4477d91e3bbf43adf4c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98815
Analysis date: Sat, 24 Oct 2026 06:40:32 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
An open NVMe character-device descriptor can outlive its freed namespace container, causing `cdev_put()` to access the embedded cdev after free during close.

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

The original Linux kernel CVE announcement for CVE-2026-98815 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98815

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
======================================================================

CVE-2026-98815	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98815 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=3 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'An NVMe character device can outlive the embedded nvme_ns or nvme_ns_head object after cdev_del because already open file descriptors remain callable. Closing such a descriptor after namespace teardown can free the containing object in release and then let cdev_put read the freed cdev memory. This is a demonstrated slab use after free with kernel crash potential. Reuse of the freed allocation before cdev_put may also affect operations involving the cdev owner or parent kobject, so memory corruption or privilege escalation requires manual investigation but is not proven. For the CVSS the PR:L value reflects that an attacker needs local access to the NVMe character device, while teardown normally requires an additional administrative action, device removal, or controller disconnect. AC:H reflects the required lifetime ordering between an open descriptor and concurrent teardown. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage IMPORTANT to MODERATE_KPANIC because the ActionableScore threshold rule was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN5. The independent weaker Aegis shadow evaluated CVSS 5.3 and ActionableScore 3 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	MAYBE	READ OOB DANGER NVME UAF KERNEL_PANIC_PLUS_UAF HARDWARE KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN5	-	-	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 3.
* Conservative score: 4. Real-UAF floor 4 applied because host-admin-only triggering is not established and an embedded active cdev is accessed after its container is freed.
* Raw paranoid score: 3.
* Paranoid score: 4. No additional exploit-leverage point is justified.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 — Demonstrated slab UAF: the close path drops the `nvme_ns_head` reference and frees the containing allocation before `cdev_put()` reads the embedded cdev.
* +1 — Plausible kernel crash/DoS, supported by the KASAN report and invalid post-free access.
* +0 — No hard-race penalty: the reproducer uses an ordered open, teardown, ioctl/close sequence rather than a proven narrow timing window.
* +0 — No privilege penalty: host-administrator control of the complete trigger is not established, although the demonstrated teardown uses an administrative sysfs operation.
* No controlled reclaim, attacker-shaped replacement, callback control, directed write, disclosure, or LPE is shown.
* This is not a repeated-release case: `nvme_put_ns_head()` can free the container, but the later `cdev_put()` is a stale embedded-object access, not a second lifetime mutation on the exact same head reference. FLOOR 5 therefore does not apply.
* No separate confidentiality or integrity point is awarded from theoretical slab reuse.

3. Reachability analysis

A local process must open the NVMe character device and retain the descriptor across namespace-head teardown. Device-node permissions are not supplied. The demonstrated teardown is performed through controller deletion by UID 0, but evidence does not show whether one below-host-admin actor can induce the complete sequence or whether teardown requires a separate administrator/device event. No namespace-scoped capability path is shown. No unusual physical hardware is required; the report reproduces under QEMU.

4. Primitive and severity reading

The primitive is a real cleanup-time UAF of an embedded active cdev after its `nvme_ns_head` container is freed. The shown stale operation is an eight-byte read in `cdev_put()` during close. It is CLASS_B, but presently constrained to teardown/close with crash behavior; useful post-reclaim consumption is not established. Thus it is not an Important candidate, while manual review remains appropriate for cdev owner/parent lifetime behavior.

5. One-sentence report phrase

An open NVMe character-device descriptor can outlive its freed namespace container, causing `cdev_put()` to access the embedded cdev after free during close.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm device-node permissions, attacker influence over teardown, and whether `cdev_put()` can consume reclaimed owner or parent state beyond the demonstrated fault.

7. Call-site confidence

Call-site confidence: high

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

Patch: nvme: fix cdev lifetime [ Upstream
Commit: 98b09ad7934482e64db4b4477d91e3bbf43adf4c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=98b09ad7934482e64db4b4477d91e3bbf43adf4c

Changed files:
  drivers/nvme/host/core.c
  drivers/nvme/host/multipath.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=98b09ad7934482e64db4b4477d91e3bbf43adf4c

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

The original Linux kernel CVE announcement for CVE-2026-98815 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98815

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:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: unknown
  Paranoid ActionableScore: 4

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).