usb: cdns3: fix use-after-free in cdns3_gadget_exit()

In the Linux kernel, the following vulnerability has been resolved: usb: cdns3: fix use-after-free in cdns3_gadget_exit() cdns3_gadget_start() arms two works on system_freezable_wq: pending_status_wq for the deferred ep0 status stage and aligned_buf_wq for realigned request buffers. Both handlers use the cdns3_device the works are embedded in, and cdns3_pending_setup_status_handler() also calls the ep0 request completion. cdns3_gadget_exit() does not wait for these works. It frees all endpoints and aligned buffers and drops the last reference to the gadget device, which frees priv_dev, so a work queued before the exit can run after the free. Fix this by waiting for both works after the gadget driver is unbound and the IRQ is freed, when no new work can be queued, and before the endpoints and buffers are released. This issue was found by an in-house static analysis tool.

Where it's fixed