usbnet: ipheth: remove extraneous rx URB length check

Rx URB length was already checked in ipheth_rcvbulk_callback_legacy()
and ipheth_rcvbulk_callback_ncm(), depending on the current mode.
The check in ipheth_rcvbulk_callback() was thus mostly a duplicate.

The only place in ipheth_rcvbulk_callback() where we care about the URB
length is for the initial control frame. These frames are always 4 bytes
long. This has been checked as far back as iOS 4.2.1 on iPhone 3G.

Remove the extraneous URB length check. For control frames, check for
the specific 4-byte length instead.
Signed-off-by: Foster Snowhill <forst@pen.gy>
Tested-by: Georgi Valkov <gvalkov@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/ipheth.c

@@ -286,11 +286,6 @@ static void ipheth_rcvbulk_callback(struct urb *urb)
 		return;
 	}
 
-	if (urb->actual_length <= IPHETH_IP_ALIGN) {
-		dev->net->stats.rx_length_errors++;
-		return;
-	}
-
 	/* RX URBs starting with 0x00 0x01 do not encapsulate Ethernet frames,
 	 * but rather are control frames. Their purpose is not documented, and
 	 * they don't affect driver functionality, okay to drop them.
@@ -298,7 +293,8 @@ static void ipheth_rcvbulk_callback(struct urb *urb)
 	 * URB received from the bulk IN endpoint.
 	 */
 	if (unlikely
-		(((char *)urb->transfer_buffer)[0] == 0 &&
+		(urb->actual_length == 4 &&
+		 ((char *)urb->transfer_buffer)[0] == 0 &&
 		 ((char *)urb->transfer_buffer)[1] == 1))
 		goto rx_submit;