[CVE-2026-64220][MODERATE 7.0] device property: set fwnode->secondary to NULL in fwnode_init()

[CVE-2026-64220][MODERATE 7.0] device property: set fwnode->secondary to NULL in fwnode_init()

[AL-KERNEL]

CVE: CVE-2026-64220
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: device property: set fwnode->secondary to NULL in fwnode_init()
Commit: f0e211d6539fae800217c10797993b7592d6ab01
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f0e211d6539fae800217c10797993b7592d6ab01
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64220
Analysis date: Fri, 24 Jul 2026 12:03:40 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
An uninitialized `fwnode->secondary` pointer in `fwnode_init()` can cause later firmware-node users to dereference stale stack or heap data, leading primarily to local kernel crash risk with weak but caller-dependent memory-safety concern.

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

The original Linux kernel CVE announcement for CVE-2026-64220 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64220

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.

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

CVE-2026-64220	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';*CWE-457;CWE-824;**CWE-476;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'fwnode_init did not clear the fwnode secondary pointer, so a firmware node allocated on the stack or by a non zeroing heap allocation could keep stale uninitialized data in this field. Later fwnode users may treat this value as a valid secondary node and dereference it, for example in dev_to_swnode, causing an invalid pointer dereference or a kernel crash. For the CVSS the PR:L is used in the paranoid score because a local user may be able to trigger an existing driver or device property path without full administrative control, although reliable triggering is driver dependent and has high complexity. The issue is not network reachable and requires a local code path that creates or exposes such fwnode objects. Impact is at least denial of service via kernel crash and in the worst case may allow limited confidentiality or integrity impact due to kernel memory safety behavior, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-64220 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	SIMPLEFIX HARDWARE  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Weak/indirect corruption candidate: +1
  `fwnode->secondary` may contain uninitialized stack or heap data and later be interpreted as a valid pointer.
* Reliable kernel crash / strong DoS: +1
  The commit explicitly states the bogus pointer may be dereferenced, for example in `dev_to_swnode()`, which can plausibly cause an Oops or kernel crash.
* Broad/default/common subsystem exposure: +1
  Device property and firmware node helpers are core driver infrastructure and are used across many subsystems.

Paranoid additional signals:

* Weak LPE concern: +1
  The primitive is a bogus kernel object pointer / invalid object interpretation. No controlled reclaim or arbitrary write is shown, so this is only weak concern.
* Privileged kernel/device-management memory corruption path: +1
  The bug occurs in trusted device-property infrastructure where corrupted object relationships can affect later kernel object traversal.

Not counted:

* No remote/network trigger: +0
* No strong generic memory corruption: +0
  This is not a demonstrated UAF, OOB write, double-free, refcount takeover, or controlled overwrite.
* No strong privilege escalation plausibility: +0
  No attacker-controlled replacement object, callback control, or write primitive is shown.
* No firmware-mediated external influence: +0
  Firmware nodes are involved, but the corrupted value is uninitialized memory, not attacker-controlled firmware input.
* No full admin penalty applied in the paranoid score because reachability depends on caller paths and may include existing driver interfaces rather than only module loading or full root control.

Call-site confidence: medium-low. The patch shows the helper and the commit names `dev_to_swnode()`, but the full set of caller paths is not provided.

## 3. Reachability analysis

There is no direct syscall or network protocol entry point to `fwnode_init()`. Triggering requires some kernel path to allocate a firmware node on the stack or through a non-zeroing heap allocation, call `fwnode_init()`, and later access `fwnode->secondary`.

In typical deployments this may be reachable only through driver-specific initialization, device-management, platform, ACPI, software-node, or firmware-node paths. Some of those paths may require root or device-management privileges, but others could potentially be reached indirectly through existing devices or subsystem-specific user interfaces. Namespaces do not obviously make this broadly unprivileged, but container or reduced-capability service contexts should be checked if they can trigger affected device-property paths.

The path is not network reachable. Exploitation conditions are caller-dependent and likely high complexity.

## 4. Severity interpretation

This behaves more like an Actionable Moderate than an ordinary low-priority cleanup because it is a kernel memory-safety issue involving an uninitialized pointer in a common core helper. The realistic impact is kernel crash or Oops from invalid pointer dereference.

Theoretical privilege escalation is not impossible because a stale-looking pointer may be interpreted as a kernel object, but the patch does not show attacker-controlled object reuse, arbitrary write, callback dispatch, refcount abuse, or a reliable corruption primitive. Therefore this should not be treated as a Strong Important candidate based on the patch alone, but it should not be auto-closed without checking real call sites.

## 5. One-sentence report phrase

An uninitialized `fwnode->secondary` pointer in `fwnode_init()` can cause later firmware-node users to dereference stale stack or heap data, leading primarily to local kernel crash risk with weak but caller-dependent memory-safety concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is not just a validation-only fix. It is an uninitialized kernel pointer bug in a common helper, and the real severity depends on which callers allocate `struct fwnode_handle`, whether local users can reach those paths, and whether any caller creates a more useful object-confusion or stale-pointer primitive.

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

Patch: device property: set fwnode->secondary to NULL in fwnode_init()
Commit: f0e211d6539fae800217c10797993b7592d6ab01
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f0e211d6539fae800217c10797993b7592d6ab01

Commit description:

If a firmware node is allocated on the stack (for instance: temporary
software node whose life-time we control) or on the heap - but using a
non-zeroing allocation function - and initialized using fwnode_init(),
its secondary pointer will contain uninitalized memory which likely will
be neither NULL nor IS_ERR() and so may end up being dereferenced (for
example: in dev_to_swnode()). Set fwnode->secondary to NULL on
initialization.

Cc: stable <stable@kernel.org>
Fixes: 01bb86b ("driver core: Add fwnode_init()")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Reviewed-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Link: https://patch.msgid.link/20260506115701.23035-1-bartosz.golaszewski@oss.qualcomm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  include/linux/fwnode.h

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=f0e211d6539fae800217c10797993b7592d6ab01

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

The original Linux kernel CVE announcement for CVE-2026-64220 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64220

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:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 3
  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).