CVE-2026-31724: usb: gadget: f_eem: Fix net_device lifecycle with device_move
In the Linux kernel, the following vulnerability has been resolved:
usb: gadget: feem: 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 f_eem net_device between the gadget device tree and /sys/devices/virtual across bind and unbind cycles; during the final unbind, call device_move(NULL) before destroying the gadget device.
Event History
Frequently Asked Questions
Who is exposed to this issue?
Systems using the Linux kernel USB gadget Ethernet Emulation Model (EEM) function are exposed when the function is bound and unbound. The vulnerability is locally exploitable and requires low privileges; no user interaction is required.
What is the practical impact of successful exploitation?
The reported CVSS vector indicates an availability impact only. Confidentiality and integrity impacts are not indicated.
How can I check for the affected lifecycle condition?
After an EEM gadget function is unbound, inspect the associated network interface under /sys/class/net, such as usb0. A symlink that still points into the removed gadget device tree while its target no longer exists indicates the dangling sysfs-link condition described.