usb: dwc3: gadget: Fix NULL pointer dereference in dwc3_gadget_suspend

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

usb: dwc3: gadget: Fix NULL pointer dereference in dwc3_gadget_suspend

In current scenario if Plug-out and Plug-In performed continuously

there could be a chance while checking for dwc->gadget_driver in

dwc3_gadget_suspend, a NULL pointer dereference may occur.

Call Stack:

CPU1: CPU2:

gadget_unbind_driver dwc3_suspend_common

dwc3_gadget_stop dwc3_gadget_suspend

dwc3_disconnect_gadget

CPU1 basically clears the variable and CPU2 checks the variable.

Consider CPU1 is running and right before gadget_driver is cleared

and in parallel CPU2 executes dwc3_gadget_suspend where it finds

dwc->gadget_driver which is not NULL and resumes execution and then

CPU1 completes execution. CPU2 executes dwc3_disconnect_gadget where

it checks dwc->gadget_driver is already NULL because of which the

NULL pointer deference occur.