Bug 2464425 (CVE-2026-31723)

Summary:	CVE-2026-31723 kernel: usb: gadget: f_subset: Fix net_device lifecycle with device_move
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	unspecified	CC:	rhel-process-autobot, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Linux kernel's usb: gadget: f_subset component. This vulnerability arises from an issue in how network device resources are managed during the unbinding of a USB gadget function. When the parent device is destroyed, the associated network device may persist, creating non-functional links in the system's file structure. This improper resource handling can lead to system instability or unexpected behavior.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-05-01 15:06:09 UTC

In the Linux kernel, the following vulnerability has been resolved:

usb: gadget: f_subset: Fix net_device lifecycle with device_move

The net_device is allocated during function instance creation and
registered during the bind phase with the gadget device as its sysfs
parent. When the function unbinds, the parent device is destroyed, but
the net_device survives, resulting in dangling sysfs symlinks:

  console:/ # ls -l /sys/class/net/usb0
  lrwxrwxrwx ... /sys/class/net/usb0 ->
  /sys/devices/platform/.../gadget.0/net/usb0
  console:/ # ls -l /sys/devices/platform/.../gadget.0/net/usb0
  ls: .../gadget.0/net/usb0: No such file or directory

Use device_move() to reparent the net_device between the gadget device
tree and /sys/devices/virtual across bind and unbind cycles. During the
final unbind, calling device_move(NULL) moves the net_device to the
virtual device tree before the gadget device is destroyed. On rebinding,
device_move() reparents the device back under the new gadget, ensuring
proper sysfs topology and power management ordering.

To maintain compatibility with legacy composite drivers (e.g., multi.c),
the bound flag is used to indicate whether the network device is shared
and pre-registered during the legacy driver's bind phase.

Comment 1 Keith Grant 2026-05-01 20:49:24 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050134-CVE-2026-31723-a0a7@gregkh/T