USB: iowarrior: fix use-after-free on release

The driver was accessing its struct usb_interface from its release()
callback without holding a reference. This would lead to a
use-after-free whenever debugging was enabled and the device was
disconnected while its character device was open.

Fixes: 549e8350 ("USB: iowarrior: Convert local dbg macro to dev_dbg")
Cc: stable <stable@vger.kernel.org>     # 3.16
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191009104846.5925-3-johan@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/iowarrior.c

@@ -243,6 +243,7 @@ static inline void iowarrior_delete(struct iowarrior *dev)
 	kfree(dev->int_in_buffer);
 	usb_free_urb(dev->int_in_urb);
 	kfree(dev->read_queue);
+	usb_put_intf(dev->interface);
 	kfree(dev);
 }
 
@@ -764,7 +765,7 @@ static int iowarrior_probe(struct usb_interface *interface,
 	init_waitqueue_head(&dev->write_wait);
 
 	dev->udev = udev;
-	dev->interface = interface;
+	dev->interface = usb_get_intf(interface);
 
 	iface_desc = interface->cur_altsetting;
 	dev->product_id = le16_to_cpu(udev->descriptor.idProduct);