mv643xx_eth: deal with unexpected ethernet header sizes

When the IP header doesn't start 14, 18, 22 or 26 bytes into the packet
(which are the only four cases that the hardware can deal with if asked
to do IP checksumming on transmit), invoke the software checksum helper
instead of letting the packet go out with a corrupt checksum inserted
into the packet in the wrong place.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>

drivers/net/mv643xx_eth.c

@@ -699,79 +699,74 @@ static inline __be16 sum16_as_be(__sum16 sum)
 	return (__force __be16)sum;
 }
 
-static void txq_submit_skb(struct tx_queue *txq, struct sk_buff *skb)
+static int txq_submit_skb(struct tx_queue *txq, struct sk_buff *skb)
 {
 	struct mv643xx_eth_private *mp = txq_to_mp(txq);
 	int nr_frags = skb_shinfo(skb)->nr_frags;
 	int tx_index;
 	struct tx_desc *desc;
 	u32 cmd_sts;
+	u16 l4i_chk;
 	int length;
 
 	cmd_sts = TX_FIRST_DESC | GEN_CRC | BUFFER_OWNED_BY_DMA;
-
-	tx_index = txq_alloc_desc_index(txq);
-	desc = &txq->tx_desc_area[tx_index];
-
-	if (nr_frags) {
-		txq_submit_frag_skb(txq, skb);
-		length = skb_headlen(skb);
-	} else {
-		cmd_sts |= ZERO_PADDING | TX_LAST_DESC | TX_ENABLE_INTERRUPT;
-		length = skb->len;
-	}
-
-	desc->byte_cnt = length;
-	desc->buf_ptr = dma_map_single(NULL, skb->data, length, DMA_TO_DEVICE);
+	l4i_chk = 0;
 
 	if (skb->ip_summed == CHECKSUM_PARTIAL) {
-		int mac_hdr_len;
+		int tag_bytes;
 
 		BUG_ON(skb->protocol != htons(ETH_P_IP) &&
 		       skb->protocol != htons(ETH_P_8021Q));
 
-		cmd_sts |= GEN_TCP_UDP_CHECKSUM |
-			   GEN_IP_V4_CHECKSUM   |
-			   ip_hdr(skb)->ihl << TX_IHL_SHIFT;
+		tag_bytes = (void *)ip_hdr(skb) - (void *)skb->data - ETH_HLEN;
+		if (unlikely(tag_bytes & ~12)) {
+			if (skb_checksum_help(skb) == 0)
+				goto no_csum;
+			kfree_skb(skb);
+			return 1;
+		}
 
-		mac_hdr_len = (void *)ip_hdr(skb) - (void *)skb->data;
-		switch (mac_hdr_len - ETH_HLEN) {
-		case 0:
-			break;
-		case 4:
-			cmd_sts |= MAC_HDR_EXTRA_4_BYTES;
-			break;
-		case 8:
-			cmd_sts |= MAC_HDR_EXTRA_8_BYTES;
-			break;
-		case 12:
+		if (tag_bytes & 4)
 			cmd_sts |= MAC_HDR_EXTRA_4_BYTES;
+		if (tag_bytes & 8)
 			cmd_sts |= MAC_HDR_EXTRA_8_BYTES;
-			break;
-		default:
-			if (net_ratelimit())
-				dev_printk(KERN_ERR, &txq_to_mp(txq)->dev->dev,
-				   "mac header length is %d?!\n", mac_hdr_len);
-			break;
-		}
+
+		cmd_sts |= GEN_TCP_UDP_CHECKSUM |
+			   GEN_IP_V4_CHECKSUM   |
+			   ip_hdr(skb)->ihl << TX_IHL_SHIFT;
 
 		switch (ip_hdr(skb)->protocol) {
 		case IPPROTO_UDP:
 			cmd_sts |= UDP_FRAME;
-			desc->l4i_chk = ntohs(sum16_as_be(udp_hdr(skb)->check));
+			l4i_chk = ntohs(sum16_as_be(udp_hdr(skb)->check));
 			break;
 		case IPPROTO_TCP:
-			desc->l4i_chk = ntohs(sum16_as_be(tcp_hdr(skb)->check));
+			l4i_chk = ntohs(sum16_as_be(tcp_hdr(skb)->check));
 			break;
 		default:
 			BUG();
 		}
 	} else {
+no_csum:
 		/* Errata BTS #50, IHL must be 5 if no HW checksum */
 		cmd_sts |= 5 << TX_IHL_SHIFT;
-		desc->l4i_chk = 0;
 	}
 
+	tx_index = txq_alloc_desc_index(txq);
+	desc = &txq->tx_desc_area[tx_index];
+
+	if (nr_frags) {
+		txq_submit_frag_skb(txq, skb);
+		length = skb_headlen(skb);
+	} else {
+		cmd_sts |= ZERO_PADDING | TX_LAST_DESC | TX_ENABLE_INTERRUPT;
+		length = skb->len;
+	}
+
+	desc->l4i_chk = l4i_chk;
+	desc->byte_cnt = length;
+	desc->buf_ptr = dma_map_single(NULL, skb->data, length, DMA_TO_DEVICE);
+
 	__skb_queue_tail(&txq->tx_skb, skb);
 
 	/* ensure all other descriptors are written before first cmd_sts */
@@ -786,6 +781,8 @@ static void txq_submit_skb(struct tx_queue *txq, struct sk_buff *skb)
 	txq_enable(txq);
 
 	txq->tx_desc_count += nr_frags + 1;
+
+	return 0;
 }
 
 static int mv643xx_eth_xmit(struct sk_buff *skb, struct net_device *dev)
@@ -794,7 +791,6 @@ static int mv643xx_eth_xmit(struct sk_buff *skb, struct net_device *dev)
 	int queue;
 	struct tx_queue *txq;
 	struct netdev_queue *nq;
-	int entries_left;
 
 	queue = skb_get_queue_mapping(skb);
 	txq = mp->txq + queue;
@@ -815,14 +811,17 @@ static int mv643xx_eth_xmit(struct sk_buff *skb, struct net_device *dev)
 		return NETDEV_TX_OK;
 	}
 
-	txq_submit_skb(txq, skb);
-	txq->tx_bytes += skb->len;
-	txq->tx_packets++;
-	dev->trans_start = jiffies;
+	if (!txq_submit_skb(txq, skb)) {
+		int entries_left;
+
+		txq->tx_bytes += skb->len;
+		txq->tx_packets++;
+		dev->trans_start = jiffies;
 
-	entries_left = txq->tx_ring_size - txq->tx_desc_count;
-	if (entries_left < MAX_SKB_FRAGS + 1)
-		netif_tx_stop_queue(nq);
+		entries_left = txq->tx_ring_size - txq->tx_desc_count;
+		if (entries_left < MAX_SKB_FRAGS + 1)
+			netif_tx_stop_queue(nq);
+	}
 
 	return NETDEV_TX_OK;
 }