rndis_wlan: prevent integer overflow in indication()

If we pick a high value for "offset" then it could lead to an integer
overflow and we would get past the check for:
	if (offset + len > buflen) { ...

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rndis_wlan.c

@@ -3043,7 +3043,7 @@ static void rndis_wlan_media_specific_indication(struct usbnet *usbdev,
 			struct rndis_indicate *msg, int buflen)
 {
 	struct ndis_80211_status_indication *indication;
-	int len, offset;
+	unsigned int len, offset;
 
 	offset = offsetof(struct rndis_indicate, status) +
 			le32_to_cpu(msg->offset);
@@ -3055,7 +3055,7 @@ static void rndis_wlan_media_specific_indication(struct usbnet *usbdev,
 		return;
 	}
 
-	if (offset + len > buflen) {
+	if (len > buflen || offset > buflen || offset + len > buflen) {
 		netdev_info(usbdev->net, "media specific indication, too large to fit to buffer (%i > %i)\n",
 			    offset + len, buflen);
 		return;