mwifiex: fix issues in driver unload path for USB chipsets

1) After driver load failure, clear 'card->adapter' instead of
card pointer so that card specific cleanup is performed later
when user unloads the driver.

2) Clear usb_card pointer in disconnect handler to avoid invalid
memory access when user unloads the driver after removing the
card.

Signed-off-by: Ujjal Roy <[e-mail]>
Signed-off-by: Amitkumar Karwar <[e-mail]>
Signed-off-by: Bing Zhao <[e-mail]>
Signed-off-by: John W. Linville <[e-mail]>

drivers/net/wireless/mwifiex/usb.c

···
 
 	card->udev = udev;
 	card->intf = intf;
-	usb_card = card;
 
 	pr_debug("info: bcdUSB=%#x Device Class=%#x SubClass=%#x Protocol=%#x\n",
 		 udev->descriptor.bcdUSB, udev->descriptor.bDeviceClass,
···
 static void mwifiex_usb_disconnect(struct usb_interface *intf)
 {
 	struct usb_card_rec *card = usb_get_intfdata(intf);
-	struct mwifiex_adapter *adapter;
 
-	if (!card || !card->adapter) {
-		pr_err("%s: card or card->adapter is NULL\n", __func__);
+	if (!card) {
+		pr_err("%s: card is NULL\n", __func__);
 		return;
 	}
 
-	adapter = card->adapter;
-	if (!adapter->priv_num)
-		return;
-
 	mwifiex_usb_free(card);
 
-	dev_dbg(adapter->dev, "%s: removing card\n", __func__);
-	mwifiex_remove_card(adapter, &add_remove_card_sem);
+	if (card->adapter) {
+		struct mwifiex_adapter *adapter = card->adapter;
+
+		if (!adapter->priv_num)
+			return;
+
+		dev_dbg(adapter->dev, "%s: removing card\n", __func__);
+		mwifiex_remove_card(adapter, &add_remove_card_sem);
+	}
 
 	usb_set_intfdata(intf, NULL);
 	usb_put_dev(interface_to_usbdev(intf));
 	kfree(card);
+	usb_card = NULL;
 
 	return;
 }
···
 	card->adapter = adapter;
 	adapter->dev = &card->udev->dev;
 	strcpy(adapter->fw_name, USB8797_DEFAULT_FW_NAME);
+	usb_card = card;
 
 	return 0;
 }
···
 {
 	struct usb_card_rec *card = (struct usb_card_rec *)adapter->card;
 
-	usb_set_intfdata(card->intf, NULL);
+	card->adapter = NULL;
 }
 
 static int mwifiex_prog_fw_w_helper(struct mwifiex_adapter *adapter,
···
 	if (!down_interruptible(&add_remove_card_sem))
 		up(&add_remove_card_sem);
 
-	if (usb_card) {
+	if (usb_card && usb_card->adapter) {
 		struct mwifiex_adapter *adapter = usb_card->adapter;
 		int i;