drivers/net/usb/asix.c: Fix unaligned accesses

Using this driver can cause unaligned accesses in the IP layer
This has been fixed by aligning the skb data correctly using the
spare room left over by the 4 byte header inserted between packets
by the device.
Signed-off-by: NNeil Jones <NeilJay@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/usb/asix.c

@@ -322,8 +322,29 @@ static int asix_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 		/* get the packet length */
 		size = (u16) (header & 0x0000ffff);
 
-		if ((skb->len) - ((size + 1) & 0xfffe) == 0)
+		if ((skb->len) - ((size + 1) & 0xfffe) == 0) {
+			u8 alignment = (u32)skb->data & 0x3;
+			if (alignment != 0x2) {
+				/*
+				 * not 16bit aligned so use the room provided by
+				 * the 32 bit header to align the data
+				 *
+				 * note we want 16bit alignment as MAC header is
+				 * 14bytes thus ip header will be aligned on
+				 * 32bit boundary so accessing ipheader elements
+				 * using a cast to struct ip header wont cause
+				 * an unaligned accesses.
+				 */
+				u8 realignment = (alignment + 2) & 0x3;
+				memmove(skb->data - realignment,
+					skb->data,
+					size);
+				skb->data -= realignment;
+				skb_set_tail_pointer(skb, size);
+			}
 			return 2;
+		}
+
 		if (size > ETH_FRAME_LEN) {
 			netdev_err(dev->net, "asix_rx_fixup() Bad RX Length %d\n",
 				   size);
@@ -331,7 +352,18 @@ static int asix_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 		}
 		ax_skb = skb_clone(skb, GFP_ATOMIC);
 		if (ax_skb) {
+			u8 alignment = (u32)packet & 0x3;
 			ax_skb->len = size;
+
+			if (alignment != 0x2) {
+				/*
+				 * not 16bit aligned use the room provided by
+				 * the 32 bit header to align the data
+				 */
+				u8 realignment = (alignment + 2) & 0x3;
+				memmove(packet - realignment, packet, size);
+				packet -= realignment;
+			}
 			ax_skb->data = packet;
 			skb_set_tail_pointer(ax_skb, size);
 			usbnet_skb_return(dev, ax_skb);