CVE-2023-53356

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

usb: gadget: u_serial: Add null pointer check in gserial_suspend

Consider a case where gserial_disconnect has already cleared
gser->ioport. And if gserial_suspend gets called afterwards,
it will lead to accessing of gser->ioport and thus causing
null pointer dereference.

Avoid this by adding a null pointer check. Added a static
spinlock to prevent gser->ioport from becoming null after
the newly added null pointer check.