[CVE-2026-89982][LOW] i2c: mux: Fix channel node leak on adapter add failure

[CVE-2026-89982][LOW] i2c: mux: Fix channel node leak on adapter add failure

[AL-KERNEL]

CVE: CVE-2026-89982
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: i2c: mux: Fix channel node leak on adapter add failure
Commit: 4f42f70afd2447f3c82ca69d1e03466a75348ba9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4f42f70afd2447f3c82ca69d1e03466a75348ba9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89982
Analysis date: Wed, 16 Sep 2026 13:42:05 -0400
ActionableScore: 0
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-2026-89982 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89982

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-2026-89982	LOW	https://www.kernelcve.org/list/?q=CVE-2026-89982 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:N/I:N/A:H';*CWE-772;CWE-404;*CWE-401;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'An I2C mux adapter add failure can leak a reference to the Device Tree channel node because i2c_mux_add_adapter() takes the node reference before registering the adapter but the error path frees private data without dropping that reference. The issue is a resource lifetime bug rather than memory corruption, and the realistic impact is limited resource leakage if the failing adapter add path can be reached repeatedly. For the CVSS the PR:L is used only for the paranoid score because triggering would require local ability to influence I2C device creation, driver binding, or Device Tree overlays. In typical systems this control is administrative and the base score uses PR:H. The issue is not network reachable. Impact is denial of service at most through resource exhaustion, with no credible confidentiality or integrity impact from the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	YES	USB SIMPLEFIX LEAK ERRORPATH HARDWARE LINUS 	NO	NO	checked

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

ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: -1
* Conservative score: 0. Raw score clamped to 0 because negative actionable scores are not useful.
* Raw paranoid score: -1
* Paranoid score: 0. No paranoid escalation is justified because the patch establishes only a missing reference release, not memory corruption or a strong DoS primitive.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Positive signals:

* +1 Concrete persistent kernel resource/reference leak. The patch directly adds `of_node_put(priv->adap.dev.of_node)` on the adapter-add failure path, establishing that a Device Tree node reference was acquired and not released.
* +0 Resource exhaustion beyond the leak itself. Repeated failures could accumulate references, but the patch does not establish fast, broad, or unprivileged host-wide exhaustion.
* +0 Reliable kernel crash / strong DoS. No crash, panic, UAF, OOB, double free, or refcount-underflow path is shown.

Negative signals:

* -2 Host-admin-equivalent device management path. Triggering this error path requires I2C mux adapter creation and registration failure, which is normally reached through driver probing, binding, Device Tree data, overlays, or hardware/device-management operations controlled by host administration.

Important non-awarded signals:

* RealUAF not awarded. The bug leaks a reference but does not use an object after its lifetime ended.
* Concrete repeated release/refcount not awarded. The problem is missing `put`, not a second `put` on a potentially dangling reference.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity not awarded because there is no disclosure path, no ownership bypass, and no unauthorized modification primitive.
* Remote reachability not established.
* Extra availability not awarded because practical host-wide exhaustion is not demonstrated.

3. Reachability analysis

The vulnerable path is in `i2c_mux_add_adapter()` during creation of an I2C mux child adapter from Device Tree channel data. An attacker would need to influence I2C device creation, driver binding/probing, Device Tree overlays, or failure of adapter registration. These are host device-management operations and are not ordinary unprivileged user interfaces.

No network path is involved. No namespace-scoped capability path is established, and I2C mux adapter creation is not a normal user or network namespace operation. Prior privileged setup is effectively required if an attacker is to influence the vulnerable path. Special hardware or platform configuration may be involved, but no separate rare-hardware penalty is needed because the host-admin requirement already captures the practical restriction.

No race is involved.

4. Primitive and severity interpretation

The exact primitive is a missing lifetime reference release: a Device Tree node reference is taken before adapter registration, and on registration failure the old error path freed private data without dropping that node reference.

This is not memory corruption. It is not active structured stale-object use. It is not fixed stale storage. It is not cleanup UAF. It is not a double release. The demonstrated consequence is a persistent reference leak, with possible low-grade resource leakage if the failure path is repeatedly reached.

PrimitiveClass is `NONE` because no meaningful corruption, authorization bypass, ownership violation, UAF, or active post-lifetime object use is established. ImportantCandidate is `NO` because the issue is a small privileged resource leak without unresolved exploitation leverage. AutoDowngradeAllowed is `YES` because the bug can be treated as ordinary low-priority resource-management cleanup unless product-specific evidence shows untrusted users can repeatedly trigger I2C adapter registration failures.

Likely operational severity: Low / ordinary Moderate at most.

5. One-sentence report phrase

An I2C mux adapter-add failure path leaked a Device Tree channel node reference by freeing private data without calling of_node_put, causing a local privileged resource leak with no evidence of memory corruption, privilege escalation, or network reachability.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: this is a concrete but small reference leak in a host-admin device-management path, with no UAF, no repeated stale refcount mutation, no corruption primitive, and no security-boundary bypass.

7. Call-site confidence

Call-site confidence: medium

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

Patch: i2c: mux: Fix channel node leak on adapter add failure
Commit: 4f42f70afd2447f3c82ca69d1e03466a75348ba9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4f42f70afd2447f3c82ca69d1e03466a75348ba9

Commit description:

i2c_mux_add_adapter() takes a reference to the Device Tree channel node
before registering the new adapter. If adapter registration fails, the
error path frees the private data without dropping that reference.

Release the channel node before freeing the private data.

Fixes: bc45449 ("i2c/of: Automatically populate i2c mux busses from device tree data.")
Signed-off-by: Ahmad Byagowi <ahmadexp@gmail.com>
Cc: <stable@vger.kernel.org> # v3.5+
Acked-by: Peter Rosin <peda@lysator.liu.se>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://patch.msgid.link/b3e46bbee781b3cb4029aca9a71316cc5e36dc17.1787502619.git.ahmadexp@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/i2c/i2c-mux.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=4f42f70afd2447f3c82ca69d1e03466a75348ba9

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

The original Linux kernel CVE announcement for CVE-2026-89982 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89982

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:L
  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: 0

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).