CVE-2026-31723: usb: gadget: f_subset: Fix net_device lifecycle with device_move
In the Linux kernel, the following vulnerability has been resolved:
usb: gadget: fsubset: Fix netdevice lifecycle with devicemove
The netdevice 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 netdevice 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 devicemove() to reparent the netdevice between the gadget device tree and /sys/devices/virtual across bind and unbind cycles. During the final unbind, calling devicemove(NULL) moves the netdevice to the virtual device tree before the gadget device is destroyed. On rebinding, devicemove() 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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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debian/linuxto a version that resolves this vulnerability.Fixed in 6.12.85-1 - Upgrade
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ubuntu/linux-nvidiato a version that resolves this vulnerability.Fixed in 7.0.0-1006.6 - Compensating control
Use device_move() to reparent the usb gadget net_device between the gadget device tree and /sys/devices/virtual across bind and unbind cycles; on final unbind, call device_move(NULL) to move the net_device to the virtual device tree before destroying the gadget device.
Event History
Frequently Asked Questions
Which systems are exposed?
Affected systems are Linux hosts using the USB gadget f_subset function where the network device can be bound and unbound from a gadget. The issue occurs across bind and unbind cycles, when the gadget parent can be destroyed while the network device remains.
What level of access does an attacker need?
The CVSS vector rates the attack as local with low privileges required and no user interaction required. It indicates high availability impact, with no confidentiality or integrity impact listed.
How can I tell whether a system is affected?
After unbinding the gadget, inspect the sysfs entry for the gadget network interface, such as /sys/class/net/usb0. A dangling symlink that points to a missing gadget-path net directory indicates the problematic lifecycle behavior.
What does the fix need to change?
The fix reparents the network device between the gadget device tree and the virtual device tree during bind and unbind operations. On final unbind, the network device is moved to the virtual device tree before the gadget device is destroyed.