forcedeth: checksum fix

The driver should inform the stack when checksum has been performed by
the HW when both IP and TCP (or UDP) checksum flags are indicated by HW.

Previously, it would also inform the stack when only IP checksum flag
was indicated by HW. This can cause data corruption when IP fragments
are used. The IP Identification field can wrap around and cause data
from new fragments to fill into older fragment slots with same IP Id.
The stack would then not perform TCP/UDP checksum (after re-assembly of
all fragments) since driver falsely stated it was already calculated.
Signed-off-by: Ayaz Abdulla <aabdulla@nvidia.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/forcedeth.c

@@ -471,9 +471,9 @@ union ring_type {
 #define NV_RX_AVAIL		(1<<31)
 
 #define NV_RX2_CHECKSUMMASK	(0x1C000000)
-#define NV_RX2_CHECKSUMOK1	(0x10000000)
-#define NV_RX2_CHECKSUMOK2	(0x14000000)
-#define NV_RX2_CHECKSUMOK3	(0x18000000)
+#define NV_RX2_CHECKSUM_IP	(0x10000000)
+#define NV_RX2_CHECKSUM_IP_TCP	(0x14000000)
+#define NV_RX2_CHECKSUM_IP_UDP	(0x18000000)
 #define NV_RX2_DESCRIPTORVALID	(1<<29)
 #define NV_RX2_SUBSTRACT1	(1<<25)
 #define NV_RX2_ERROR1		(1<<18)
@@ -2375,14 +2375,9 @@ static int nv_rx_process(struct net_device *dev, int limit)
 						goto next_pkt;
 					}
 				}
-				if ((flags & NV_RX2_CHECKSUMMASK) == NV_RX2_CHECKSUMOK2)/*ip and tcp */ {
+				if (((flags & NV_RX2_CHECKSUMMASK) == NV_RX2_CHECKSUM_IP_TCP) || /*ip and tcp */
+				    ((flags & NV_RX2_CHECKSUMMASK) == NV_RX2_CHECKSUM_IP_UDP))   /*ip and udp */
 					skb->ip_summed = CHECKSUM_UNNECESSARY;
-				} else {
-					if ((flags & NV_RX2_CHECKSUMMASK) == NV_RX2_CHECKSUMOK1 ||
-					    (flags & NV_RX2_CHECKSUMMASK) == NV_RX2_CHECKSUMOK3) {
-						skb->ip_summed = CHECKSUM_UNNECESSARY;
-					}
-				}
 			} else {
 				dev_kfree_skb(skb);
 				goto next_pkt;
@@ -2474,14 +2469,9 @@ static int nv_rx_process_optimized(struct net_device *dev, int limit)
 				}
 			}
 
-			if ((flags & NV_RX2_CHECKSUMMASK) == NV_RX2_CHECKSUMOK2)/*ip and tcp */ {
+			if (((flags & NV_RX2_CHECKSUMMASK) == NV_RX2_CHECKSUM_IP_TCP) || /*ip and tcp */
+			    ((flags & NV_RX2_CHECKSUMMASK) == NV_RX2_CHECKSUM_IP_UDP))   /*ip and udp */
 				skb->ip_summed = CHECKSUM_UNNECESSARY;
-			} else {
-				if ((flags & NV_RX2_CHECKSUMMASK) == NV_RX2_CHECKSUMOK1 ||
-				    (flags & NV_RX2_CHECKSUMMASK) == NV_RX2_CHECKSUMOK3) {
-					skb->ip_summed = CHECKSUM_UNNECESSARY;
-				}
-			}
 
 			/* got a valid packet - forward it to the network core */
 			skb_put(skb, len);