pktgen: fix UDP checksum computation

This patch fixes two issues in UDP checksum computation in pktgen.

First, the pseudo-header uses the source and destination IP
addresses. Currently, the ports are used for IPv4.

Second, the UDP checksum covers both header and data.  So we need to
generate the data earlier (move pktgen_finalize_skb up), and compute
the checksum for UDP header + data.

Fixes: c26bf4a51308c ("pktgen: Add UDPCSUM flag to support UDP checksums")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/pktgen.c

@@ -2842,25 +2842,25 @@ static struct sk_buff *fill_packet_ipv4(struct net_device *odev,
 	skb->dev = odev;
 	skb->pkt_type = PACKET_HOST;
 
+	pktgen_finalize_skb(pkt_dev, skb, datalen);
+
 	if (!(pkt_dev->flags & F_UDPCSUM)) {
 		skb->ip_summed = CHECKSUM_NONE;
 	} else if (odev->features & NETIF_F_V4_CSUM) {
 		skb->ip_summed = CHECKSUM_PARTIAL;
 		skb->csum = 0;
-		udp4_hwcsum(skb, udph->source, udph->dest);
+		udp4_hwcsum(skb, iph->saddr, iph->daddr);
 	} else {
-		__wsum csum = udp_csum(skb);
+		__wsum csum = skb_checksum(skb, skb_transport_offset(skb), datalen + 8, 0);
 
 		/* add protocol-dependent pseudo-header */
-		udph->check = csum_tcpudp_magic(udph->source, udph->dest,
+		udph->check = csum_tcpudp_magic(iph->saddr, iph->daddr,
 						datalen + 8, IPPROTO_UDP, csum);
 
 		if (udph->check == 0)
 			udph->check = CSUM_MANGLED_0;
 	}
 
-	pktgen_finalize_skb(pkt_dev, skb, datalen);
-
 #ifdef CONFIG_XFRM
 	if (!process_ipsec(pkt_dev, skb, protocol))
 		return NULL;
@@ -2976,6 +2976,8 @@ static struct sk_buff *fill_packet_ipv6(struct net_device *odev,
 	skb->dev = odev;
 	skb->pkt_type = PACKET_HOST;
 
+	pktgen_finalize_skb(pkt_dev, skb, datalen);
+
 	if (!(pkt_dev->flags & F_UDPCSUM)) {
 		skb->ip_summed = CHECKSUM_NONE;
 	} else if (odev->features & NETIF_F_V6_CSUM) {
@@ -2984,7 +2986,7 @@ static struct sk_buff *fill_packet_ipv6(struct net_device *odev,
 		skb->csum_offset = offsetof(struct udphdr, check);
 		udph->check = ~csum_ipv6_magic(&iph->saddr, &iph->daddr, udplen, IPPROTO_UDP, 0);
 	} else {
-		__wsum csum = udp_csum(skb);
+		__wsum csum = skb_checksum(skb, skb_transport_offset(skb), udplen, 0);
 
 		/* add protocol-dependent pseudo-header */
 		udph->check = csum_ipv6_magic(&iph->saddr, &iph->daddr, udplen, IPPROTO_UDP, csum);
@@ -2993,8 +2995,6 @@ static struct sk_buff *fill_packet_ipv6(struct net_device *odev,
 			udph->check = CSUM_MANGLED_0;
 	}
 
-	pktgen_finalize_skb(pkt_dev, skb, datalen);
-
 	return skb;
 }