rt2x00: fix possible memory corruption in case of invalid rxdesc.size

Sometimes rxdesc descriptor provided by hardware contains invalid
(random) data. For example rxdesc.size can be bigger than actual
size of the buffer. When this happen rt2x00crypto_rx_insert_iv()
corrupt memory doing memmove outside of buffer boundaries.
Signed-off-by: Stanislaw Gruszka <stf_xl@wp.pl>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2x00dev.c

@@ -582,6 +582,18 @@ void rt2x00lib_rxdone(struct queue_entry *entry)
 	memset(&rxdesc, 0, sizeof(rxdesc));
 	rt2x00dev->ops->lib->fill_rxdone(entry, &rxdesc);
 
+	/*
+	 * Check for valid size in case we get corrupted descriptor from
+	 * hardware.
+	 */
+	if (unlikely(rxdesc.size == 0 ||
+		     rxdesc.size > entry->queue->data_size)) {
+		WARNING(rt2x00dev, "Wrong frame size %d max %d.\n",
+			rxdesc.size, entry->queue->data_size);
+		dev_kfree_skb(entry->skb);
+		goto renew_skb;
+	}
+
 	/*
 	 * The data behind the ieee80211 header must be
 	 * aligned on a 4 byte boundary.
@@ -642,6 +654,7 @@ void rt2x00lib_rxdone(struct queue_entry *entry)
 
 	ieee80211_rx_ni(rt2x00dev->hw, entry->skb);
 
+renew_skb:
 	/*
 	 * Replace the skb with the freshly allocated one.
 	 */