CVE-2026-64346: usb: gadget: udc: Fix use-after-free in gadget_match_driver

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

usb: gadget: udc: Fix use-after-free in gadgetmatchdriver

The udc structure acts as the management structure for the gadget, but their lifecycles are decoupled. A race condition exists where usbdelgadget() frees the udc memory (e.g., via mode-switch work) while gadgetmatchdriver() concurrently accesses the freed udc memory (e.g., via configfs), causing a Use-After-Free (UAF) that triggers a NULL pointer dereference when the freed memory is zeroed:

[39430.908615][ T1171] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 [39430.911397][ T1171] pc : pistrcmp+0x20/0x140 [39430.911441][ T1171] lr : gadgetmatchdriver+0x34/0x60 ... [39430.911890][ T1171] usbgadgetregisterdriverowner+0x50/0xf8 [39430.911910][ T1171] gadgetdevdescUDCstore+0xf4/0x140 [39430.931308][ T1171] configfswriteiter+0xec/0x134

[39430.957058][ T1171] Workqueue: eventsfreezable dwc3setmode [39430.957287][ T1171] dwc3gadgetexit+0x34/0x8c [39430.957304][ T1171] dwc3setmode+0xc0/0x664

Fix this by ensuring the udc structure remains allocated until the gadget is released. To achieve this, introduce a new usbgadgetrelease() routine to the core. When the gadget is added, usbaddgadget() stores the gadget's release routine in the udc structure and takes a reference to the udc. When the gadget is released, usbgadgetrelease() drops the reference to the udc and then calls the gadget's release routine.