r8152: add skb_cow_head

Call skb_cow_head() before editing the tx packet header. The header
would be reallocated if it is shared.

Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/r8152.c

@@ -1376,6 +1376,11 @@ static int msdn_giant_send_check(struct sk_buff *skb)
 {
 	const struct ipv6hdr *ipv6h;
 	struct tcphdr *th;
+	int ret;
+
+	ret = skb_cow_head(skb, 0);
+	if (ret)
+		return ret;
 
 	ipv6h = ipv6_hdr(skb);
 	th = tcp_hdr(skb);
@@ -1383,7 +1388,7 @@ static int msdn_giant_send_check(struct sk_buff *skb)
 	th->check = 0;
 	th->check = ~tcp_v6_check(0, &ipv6h->saddr, &ipv6h->daddr, 0);
 
-	return 0;
+	return ret;
 }
 
 static int r8152_tx_csum(struct r8152 *tp, struct tx_desc *desc,
@@ -1412,8 +1417,11 @@ static int r8152_tx_csum(struct r8152 *tp, struct tx_desc *desc,
 			break;
 
 		case htons(ETH_P_IPV6):
+			if (msdn_giant_send_check(skb)) {
+				ret = TX_CSUM_TSO;
+				goto unavailable;
+			}
 			opts1 |= GTSENDV6;
-			msdn_giant_send_check(skb);
 			break;
 
 		default: