[CVE-2026-89744][LOW] device property: fix infinite loop in fwnode_for_each_child_node()

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

CVE: CVE-2026-89744
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: device property: fix infinite loop in fwnode_for_each_child_node()
Commit: 20ed517e416df89448029293304c9e180c26cd4b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=20ed517e416df89448029293304c9e180c26cd4b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89744
Analysis date: Fri, 11 Sep 2026 17:59:22 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89744 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89744

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: LOW
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-2026-89744	LOW	https://www.kernelcve.org/list/?q=CVE-2026-89744 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';*CWE-835;**CWE-400;CWE-691;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.4';DESCR 'A logic bug in device property child iteration can make fwnode_get_next_child_node() cycle indefinitely when a primary fwnode has a secondary fwnode and the secondary side has multiple children. A kernel caller using fwnode_for_each_child_node() may repeatedly receive children from the primary list again after reaching a secondary child, causing an infinite loop and CPU consumption in the caller context. For the CVSS the PR:H is typical because constructing or exposing such fwnode topology normally requires privileged firmware, ACPI, device tree, or driver controlled configuration rather than ordinary local user actions. The issue is not network reachable. Impact is denial of service only through a stuck kernel loop or stalled device probing path, with no evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	INIT HARDWARE 	YES	NO	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

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

2. Signal breakdown

Positive signals:

* +1 Reliable DoS / availability impact: the patch and commit establish an infinite loop in fwnode_for_each_child_node() users when primary and secondary fwnode child iteration is mixed incorrectly.

Negative signals:

* No negative privilege penalty applied. Host-admin-equivalent reachability is plausible due to firmware, ACPI, device tree, or driver-controlled topology, but it is not fully proven from the supplied input.
* No race penalty applied. This is deterministic iterator logic, not a timing race.
* No rare hardware penalty applied. The specific topology may be uncommon, but the supplied evidence does not establish a physical-only or rare-hardware-only prerequisite.

Non-awarded material signals:

* RealUAF not awarded. No freed object, stale post-lifetime use, double release, or refcount mutation is established.
* Memory corruption not awarded. The bug is an iterator parent-selection logic error causing repeated traversal.
* Controlled reclaim, arbitrary write, OOB access, information disclosure, and privilege escalation are not demonstrated.
* Remote reachability not awarded. The trigger is fwnode topology and kernel iteration, not attacker-controlled network traffic.
* Extra availability point not awarded because the same infinite loop is already counted as the DoS signal.
* Concrete repeated release/refcount signal not applicable. There is no first release, surviving exact reference, or second lifetime-mutating operation.
* FLOOR 5 not applied. There is no UAF, no active structured stale object exploitation surface, and no repeated lifetime/refcount mutation.

3. Reachability analysis

The apparent trigger requires a kernel caller to iterate children of a fwnode that has a secondary fwnode with a topology matching the described primary and secondary child layout. Ordinary local user reachability is not established. Network reachability is not established.

The likely practical sources of such topology are firmware descriptions, ACPI, device tree, software nodes, or driver-created secondary fwnode relationships. Those are commonly controlled by firmware, platform configuration, or privileged driver/device setup, but the supplied input does not conclusively prove that host-admin-equivalent privilege is required for every affected call path. Therefore HostAdminRequired is UNKNOWN rather than YES.

No namespace-scoped privilege path is shown. There is no evidence that an attacker can create the required fwnode topology inside an attacker-controlled namespace. NamespaceScopedPrivilege is NO.

No special timing is needed. If the affected topology is present and a caller uses fwnode_for_each_child_node(), the loop behavior appears deterministic.

4. Primitive and severity interpretation

The exact primitive is an infinite loop caused by calling get_next_child_node() on the wrong parent after iteration has moved from the primary fwnode to a secondary fwnode child. This can repeatedly return primary children again and prevent iteration from terminating.

This is not an active structured UAF and not fixed stale storage. It is a logic bug in traversal state handling. There is no cleanup/destructor UAF, no broader post-lifetime processing, and no concrete repeated release/refcount operation.

PrimitiveClass is CLASS_C because the demonstrated behavior is DoS/invalid-state looping without an independently useful corruption primitive. The demonstrated consequence is CPU consumption or a stuck kernel caller context, potentially affecting probing or device-property iteration. The speculative consequence remains DoS only. There is no supported path to confidentiality impact, integrity impact, or privilege escalation.

ImportantCandidate is NO because there is no memory corruption, ownership violation, authorization bypass, security-boundary primitive, or unresolved lifetime/refcount corruption leverage. AutoDowngradeAllowed is YES because this is a constrained logic DoS suitable for ordinary Moderate or Low-like handling unless product-specific evidence shows unprivileged creation of the affected topology.

5. One-sentence report phrase

A device property iterator logic bug can make fwnode_for_each_child_node() loop indefinitely when primary and secondary fwnodes are mixed, causing CPU consumption or a stuck kernel caller context without evidence of memory corruption or privilege escalation.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the supplied evidence supports a deterministic DoS-only iterator logic bug with no UAF, corruption primitive, authorization bypass, network trigger, or privilege-escalation path.

7. Call-site confidence

Call-site confidence: medium

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

Patch: device property: fix infinite loop in fwnode_for_each_child_node()
Commit: 20ed517e416df89448029293304c9e180c26cd4b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=20ed517e416df89448029293304c9e180c26cd4b

Commit description:

When iterate over children of a fwnode that has a secondary fwnode,
fwnode_get_next_child_node() can enter an infinite loop if the secondary
fwnode has more than one child.

                       Parent        Child
      (Primary fwnode)   FWa:   {FWa1, FWa2, FWa3}
    (Secondary fwnode)   FWb:   {FWb1, FWb2}

In this case:

 ┌─> fwnode_get_next_child_node(FWa, FWa1)
 │    - fwnode_call_ptr_op(FWa, get_next_child_node, FWa1) returns FWa2
 │
 │   ...
 │
 │   fwnode_get_next_child_node(FWa, FWa3)
 │    - fwnode_call_ptr_op(FWa, get_next_child_node, FWa3) returns NULL
 │    - fwnode_call_ptr_op(FWb, get_next_child_node, FWa3) returns FWb1
 │
 │   fwnode_get_next_child_node(FWa, FWb1)
 │    - fwnode_call_ptr_op(FWa, get_next_child_node, FWb1) returns FWa1
 └────┘

This cause fwnode_for_each_child_node() to loop indefinitely, reapeatedly
output {FWa1, FWa2, FWa3, FWb1, FWa1, ...}.

The root cause is that when the current child (FWb1) belongs to the
secondary fwnode, calling get_next_child_node() on the parimary fwnode
incorrectly returns the first child (FWa1) again instead of NULL.

Fix this by dynamically checking the parent fwnode of the current child
before calling get_next_child_node(). This approach follows the pattern
established in commit b5b41ab ("device property: Check
fwnode->secondary in fwnode_graph_get_next_endpoint()").

Fixes: 2692c61 ("device property: Allow secondary lookup in fwnode_get_next_child_node()")
Cc: stable@vger.kernel.org
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
Tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Xu Yang <xu.yang_2@nxp.com>
Link: https://patch.msgid.link/20260611203537.1786399-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/base/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=20ed517e416df89448029293304c9e180c26cd4b

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

The original Linux kernel CVE announcement for CVE-2026-89744 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89744

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:L/PR:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.4

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).