[CVE-2026-98504][MODERATE REGULAR] PCI: of_property: Omit bus properties without a subordinate bus

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

CVE: CVE-2026-98504
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: PCI: of_property: Omit bus properties without a subordinate bus
Commit: ccd32fa3489cbe86a0b281da4447b4c7eadb3518
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ccd32fa3489cbe86a0b281da4447b4c7eadb3518
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98504
Analysis date: Mon, 19 Oct 2026 00:59:16 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A missing subordinate bus check in the PCI dynamic OF property helpers can cause a NULL pointer dereference and early boot hang on a specific PCI topology, with no supported memory corruption, authorization bypass, or remote trigger.

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

The original Linux kernel CVE announcement for CVE-2026-98504 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98504

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 REGULAR
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-2026-98504	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98504 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=0 LEGACY=MODERATE RESULT=SAME V39_AEGIS_ONE_STEP_UP=LOW->MODERATE (final reconciliation agrees; DECISION: both MODERATE)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'The PCI dynamic OF property helpers can dereference a NULL subordinate bus when a bridge has no allocated secondary bus. This requires CONFIG_PCI_DYNAMIC_OF_NODES and a specific PCI topology in which the bridge exists but no subordinate bus was created. The resulting NULL pointer dereference can hang the system during early boot and therefore causes a denial of service. The issue is not network reachable and ordinary local applications cannot directly create the required PCI topology. For the CVSS the PR:L value in the paranoid score represents an environment where a reduced capability management account or virtual machine operator has delegated control over virtual PCI topology or device hotplug. There is no supported UAF, OOB access, information disclosure, arbitrary write, or privilege escalation primitive. Impact is limited to availability. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE to LOW because the CVSS score, vector or bug class threshold rule was applied. final reconciliation stage LOW to MODERATE because the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 4.2 and ActionableScore 0 with primitive class CLASS_C and manual review NO. Its independently reconciled impact was MODERATE. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	NULLPTR SIMPLEFIX HARDWARE LINUS TEST DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

## 1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

## 2. Signal breakdown

Positive signals:

* +1 Reliable strong DoS. The commit explicitly establishes a NULL pointer dereference and early boot hang when dynamic OF properties are generated for a PCI bridge without a subordinate bus.

Negative signals:

* No numerical penalty. `CONFIG_PCI_DYNAMIC_OF_NODES` and the required PCI topology restrict exposure, but a configuration option alone does not justify the rare-subsystem penalty.

Important non-awarded signals:

* No UAF, OOB read, OOB write, stale object, refcount error, or active-state corruption is established.
* No attacker-controlled payload or corruption target exists.
* No authorization decision changes from DENY to ALLOW.
* No confidentiality, integrity, privilege-escalation, or protected-resource impact is supported.
* Remote and namespace-based reachability are not established.
* B5-R does not apply because there is no retry-accumulated heap write.
* B3-PENDING does not apply because there is no shared-backing write.
* V32, V33, and V34 do not apply because no attacker-controlled SKB metadata or downstream networking consumer is involved.
* No extra Availability point is awarded because the early boot hang is the same consequence already counted as strong DoS.

## 3. Reachability analysis

The vulnerable path requires `CONFIG_PCI_DYNAMIC_OF_NODES`, creation of a dynamic OF node, and a Type 1 PCI bridge for which no subordinate bus was allocated. This can occur when bus numbers are exhausted or the bridge bus-number registers are not writable.

Ordinary local users cannot directly construct this boot-time PCI topology through the shown interface. A firmware, physical-device, hypervisor, or platform-management influence is conceivable, but the supplied evidence does not establish a complete attacker-controlled trigger or its required privilege. Therefore `HostAdminRequired=UNKNOWN` rather than assuming either host administration or below-admin reachability.

The operation is not namespace-scoped. There is no race, repeatable userspace retry sequence, network trigger, or demonstrated delegated-device interface. The configuration and topology prerequisites reduce practical exposure but do not change the demonstrated early boot failure.

## 4. Primitive and severity interpretation

The exact primitive is a NULL pointer dereference of `pdev->subordinate` while constructing `bus-range` or `interrupt-map` properties. This is an invalid-state dereference, not memory corruption or a lifetime violation.

The demonstrated consequence is an early boot hang and loss of availability. There is no write primitive, stale allocation, active structured-state corruption, security-boundary crossing, or useful behavior beyond the fault. The patch-supported classification is therefore `CLASS_C`.

`ImportantCandidate=NO` because no Important-preserving primitive or unresolved cross-boundary corruption chain exists. `AutoDowngradeAllowed=YES` because the issue is a configuration-dependent crash-only defect without UAF, authorization bypass, or attacker-controlled corruption.

Likely operational severity is Low to ordinary Moderate, depending on whether the affected platform can encounter bridges without subordinate buses during boot.

## 5. One-sentence report phrase

A missing subordinate bus check in the PCI dynamic OF property helpers can cause a NULL pointer dereference and early boot hang on a specific PCI topology, with no supported memory corruption, authorization bypass, or remote trigger.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes only a configuration-dependent NULL dereference and boot-time DoS, with no unresolved corruption or security-boundary primitive.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: PCI: of_property: Omit bus properties without a subordinate bus
Commit: ccd32fa3489cbe86a0b281da4447b4c7eadb3518
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ccd32fa3489cbe86a0b281da4447b4c7eadb3518

Commit description:

A bridge (a device with a Type 1 header) may not have a secondary bus
allocated (pdev->subordinate), e.g., if there are no available bus numbers
or the bridge secondary/subordinate bus numbers are not writable.

The dynamic OF helpers of_pci_prop_bus_range() and of_pci_prop_intr_map()
dereference pdev->subordinate without checking it.  When
CONFIG_PCI_DYNAMIC_OF_NODES is enabled, this can cause a NULL pointer
dereference and early boot hang.

Generate 'bus-range' and 'interrupt-map' properties only when a subordinate
bus exists.  Keep the node and its remaining properties for bridges without
one.

The problem was latent since 407d1a5 ("PCI: Create device tree node
for bridge"), but wasn't reachable until 1f34072 ("PCI: of: Create
device tree PCI host bridge node"), which appeared in v6.15.  Before
1f34072 , of_pci_make_dev_node() returned early because the parent OF
node was missing.

Fixes: 407d1a5 ("PCI: Create device tree node for bridge")
Signed-off-by: Angel J <iamanaws@httpd.dev>
[bhelgaas: move pdev->subordinate test to callees, commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org	# v6.6+
Link: https://patch.msgid.link/20260918195540.GA1187209@bhelgaas
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/pci/of_property.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=ccd32fa3489cbe86a0b281da4447b4c7eadb3518

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

The original Linux kernel CVE announcement for CVE-2026-98504 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98504

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:H/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:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 1

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 REGULAR

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).