asix: Ensure asix_rx_fixup_info members are all reset

There is a risk that the members of the structure asix_rx_fixup_info
become unsynchronised leading to the possibility of a malfunction.

For example, rx->split_head was not being set to false after an
error was detected so potentially could cause a malformed 32-bit
Data header word to be formed.

Therefore add function reset_asix_rx_fixup_info() to reset all the
members of asix_rx_fixup_info so that future processing will start
with known initial conditions.

Also, if (skb->len != offset) becomes true then call
reset_asix_rx_fixup_info() so that the processing of the next URB
starts with known initial conditions. Without the call, the check
does nothing which potentially could lead to a malfunction
when the next URB is processed.

In addition, for robustness, call reset_asix_rx_fixup_info() before
every error path's "return 0". This ensures that the next URB is
processed from known initial conditions.

Signed-off-by: Dean Jenkins <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/usb/asix_common.c

···
 			       value, index, data, size);
 }
 
+static void reset_asix_rx_fixup_info(struct asix_rx_fixup_info *rx)
+{
+	/* Reset the variables that have a lifetime outside of
+	 * asix_rx_fixup_internal() so that future processing starts from a
+	 * known set of initial conditions.
+	 */
+
+	if (rx->ax_skb) {
+		/* Discard any incomplete Ethernet frame in the netdev buffer */
+		kfree_skb(rx->ax_skb);
+		rx->ax_skb = NULL;
+	}
+
+	/* Assume the Data header 32-bit word is at the start of the current
+	 * or next URB socket buffer so reset all the state variables.
+	 */
+	rx->remaining = 0;
+	rx->split_head = false;
+	rx->header = 0;
+}
+
 int asix_rx_fixup_internal(struct usbnet *dev, struct sk_buff *skb,
 			   struct asix_rx_fixup_info *rx)
 {
···
 		if (size != ((~rx->header >> 16) & 0x7ff)) {
 			netdev_err(dev->net, "asix_rx_fixup() Data Header synchronisation was lost, remaining %d\n",
 				   rx->remaining);
-			if (rx->ax_skb) {
-				kfree_skb(rx->ax_skb);
-				rx->ax_skb = NULL;
-				/* Discard the incomplete netdev Ethernet frame
-				 * and assume the Data header is at the start of
-				 * the current URB socket buffer.
-				 */
-			}
-			rx->remaining = 0;
+			reset_asix_rx_fixup_info(rx);
 		}
 	}
 
···
 			if (size != ((~rx->header >> 16) & 0x7ff)) {
 				netdev_err(dev->net, "asix_rx_fixup() Bad Header Length 0x%x, offset %d\n",
 					   rx->header, offset);
+				reset_asix_rx_fixup_info(rx);
 				return 0;
 			}
 			if (size > dev->net->mtu + ETH_HLEN + VLAN_HLEN) {
 				netdev_dbg(dev->net, "asix_rx_fixup() Bad RX Length %d\n",
 					   size);
+				reset_asix_rx_fixup_info(rx);
 				return 0;
 			}
 
···
 	if (skb->len != offset) {
 		netdev_err(dev->net, "asix_rx_fixup() Bad SKB Length %d, %d\n",
 			   skb->len, offset);
+		reset_asix_rx_fixup_info(rx);
 		return 0;
 	}