rt2800usb: Added rx packet length validity check

On our system (ARM Cortex-M3 SOC running linux-2.6.33)
frequent crashes were observed in the rt2800usb module
because of the invalid length of the received packet (3392,
46920...). This patch adds the sanity check on the packet
legth. Also, changed WARNING to ERROR in rt2x00lib_rxdone()
so that the bad packet condition would be noticed.

The fix was tested on the latest compat-wireless-3.5.1-1-snpc.

Cc: stable@vger.kernel.org
Signed-off-by: Sergei Poselenov <sposelenov@emcraft.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2800usb.c

@@ -667,8 +667,16 @@ static void rt2800usb_fill_rxdone(struct queue_entry *entry,
 	skb_pull(entry->skb, RXINFO_DESC_SIZE);
 
 	/*
-	 * FIXME: we need to check for rx_pkt_len validity
+	 * Check for rx_pkt_len validity. Return if invalid, leaving
+	 * rxdesc->size zeroed out by the upper level.
 	 */
+	if (unlikely(rx_pkt_len == 0 ||
+			rx_pkt_len > entry->queue->data_size)) {
+		ERROR(entry->queue->rt2x00dev,
+			"Bad frame size %d, forcing to 0\n", rx_pkt_len);
+		return;
+	}
+
 	rxd = (__le32 *)(entry->skb->data + rx_pkt_len);
 
 	/*

drivers/net/wireless/rt2x00/rt2x00dev.c

@@ -629,7 +629,7 @@ void rt2x00lib_rxdone(struct queue_entry *entry, gfp_t gfp)
 	 */
 	if (unlikely(rxdesc.size == 0 ||
 		     rxdesc.size > entry->queue->data_size)) {
-		WARNING(rt2x00dev, "Wrong frame size %d max %d.\n",
+		ERROR(rt2x00dev, "Wrong frame size %d max %d.\n",
 			rxdesc.size, entry->queue->data_size);
 		dev_kfree_skb(entry->skb);
 		goto renew_skb;