[CVE-2026-64347][MODERATE REGULAR] usb: gadget: composite: fix dead empty check in the USB_DT_OTG handler

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

CVE: CVE-2026-64347
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: usb: gadget: composite: fix dead empty check in the USB_DT_OTG handler
Commit: 2454264b2ab4cf0055c0bfd39e79f830452bd0db
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2454264b2ab4cf0055c0bfd39e79f830452bd0db
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64347
Analysis date: Sat, 25 Jul 2026 09:26:28 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A USB gadget composite OTG request can interpret an empty configuration list as a valid configuration object, allowing a malicious USB host to trigger an invalid kernel read that may leak limited kernel data in the control response or crash the gadget kernel.

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

The original Linux kernel CVE announcement for CVE-2026-64347 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64347

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: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-64347	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H';CWE-125;**CWE-476;CWE-362;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '5.7';DESCR 'The USB gadget composite USB_DT_OTG handler can use list_first_entry() on an empty cdev configs list and treat the list head as a usb_configuration object. This makes config descriptors point to unrelated kernel memory and can lead to an invalid read during memcpy into the USB control response buffer. A malicious USB host can trigger the vulnerable path when the gadget has no active configurations, for example during a teardown race or during an invalid gadget driver initialization window. For the CVSS the PR:N is used because the attacker does not need credentials on the gadget device, only access to the USB host side of the connection. The issue is not network reachable and requires physical or USB bus access. Impact is at least denial of service via kernel crash, with a plausible confidentiality impact because bytes copied from an unintended kernel address may be returned in the USB response.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)	YES	KASAN USB RACE IMPROVEONLY LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Weak/indirect corruption candidate: +1. `list_first_entry()` on an empty list makes the list head be interpreted as `struct usb_configuration`, which is bogus struct interpretation.
* Reliable kernel crash / strong DoS: +1. The commit states that a reproducer triggers a KASAN fault in this branch.
* Confidentiality impact plausible: +1. `memcpy(req->buf, config->descriptors[0], value)` may copy bytes from an unintended kernel-derived address into a USB control response.
* Physical-only condition: -2. The attacker needs USB host-side or USB bus access to the gadget device.

Paranoid additional interpretation:

* Privileged kernel/device-management memory corruption path: +1. The bug is in USB gadget control handling and involves invalid interpretation of kernel device configuration state during teardown or incomplete initialization.

Not counted:

* No remote/network reachability.
* No strong LPE plausibility. There is no write-after-free, controlled reclaim, callback control, arbitrary write, or refcount takeover shown.
* No strong generic memory corruption. The demonstrated primitive is invalid read / bogus object interpretation, not an OOB write or UAF reclaim primitive.
* No Dirty-Pipe-like or page-cache corruption primitive.

## 3. Reachability analysis

A malicious USB host can trigger the vulnerable request path if the Linux system is acting as a USB gadget and the composite device has `is_otg` set while `cdev->configs` is empty. This can happen during a teardown race on gadget unbind with a control transfer in flight, or in a buggy gadget driver initialization window before a configuration is added.

No local Linux user account is required on the gadget device from the attacker side, but the attack is physical or USB-bus adjacent, not network reachable. Namespaces and containers do not materially lower the requirement, because the trigger is from the USB host side and depends on gadget-mode exposure. The path is not universally default-enabled on general servers, but it is relevant for embedded devices, phones, development boards, and systems using USB gadget/composite functionality.

Call-site confidence: high. The vulnerable call site and the later `memcpy()` use are visible in the provided patch context.

## 4. Severity interpretation

This behaves more like a borderline actionable Moderate than an Important-class kernel vulnerability. The realistic demonstrated impact is kernel crash or KASAN fault, with plausible information disclosure because an unintended pointer may be used as the source for data copied into a USB response buffer.

Theoretical memory-corruption potential is limited. The patch supports invalid object interpretation and invalid read, but does not show attacker-controlled overwrite, UAF reclaim, type confusion with write capability, or a practical privilege-escalation path. Because the bug is physical-access only and requires a special empty-configuration state, it should not be scored like a remote or local unprivileged LPE.

## 5. One-sentence report phrase

A USB gadget composite OTG request can interpret an empty configuration list as a valid configuration object, allowing a malicious USB host to trigger an invalid kernel read that may leak limited kernel data in the control response or crash the gadget kernel.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the bug is physical-only and not an Important candidate by default, but it involves bogus kernel object interpretation followed by copying data into an attacker-visible USB response buffer, so the possible confidentiality impact should be manually checked before auto-closing.

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

Patch: usb: gadget: composite: fix dead empty check in the USB_DT_OTG handler
Commit: 2454264b2ab4cf0055c0bfd39e79f830452bd0db
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2454264b2ab4cf0055c0bfd39e79f830452bd0db

Commit description:

The OTG branch of composite_setup() falls back to the first
configuration when none is selected:

	if (cdev->config)
		config = cdev->config;
	else
		config = list_first_entry(&cdev->configs,
					  struct usb_configuration, list);
	if (!config)
		goto done;
	...
	memcpy(req->buf, config->descriptors[0], value);

list_first_entry() never returns NULL. On an empty list it returns
container_of() of the list head. So the "if (!config)" check is dead.

When cdev->configs is empty, config points at the head inside struct
usb_composite_dev. config->descriptors[0] reads whatever sits at that
offset. The memcpy copies up to w_length bytes of it into the response
buffer.

cdev->configs can be empty in two cases. One is a teardown race on
gadget unbind with a control transfer in flight. The other is a driver
that sets is_otg before it adds a config. A reproducer that holds
cdev->configs empty triggers a KASAN fault in this branch.

Use list_first_entry_or_null() so the existing check does its job.

Fixes: 53e6242 ("usb: gadget: composite: add USB_DT_OTG request handling")
Cc: stable <stable@kernel.org>
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
Link: https://patch.msgid.link/20260527150832.2943293-1-maoyixie.tju@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/gadget/composite.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=2454264b2ab4cf0055c0bfd39e79f830452bd0db

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

The original Linux kernel CVE announcement for CVE-2026-64347 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64347

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:P/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS vector: AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H
  The Best / paranoid CVSS score: 5.7

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: 2
  Paranoid ActionableScore: 3

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).