l2tp: Add support for zero IPv6 checksums

Added new L2TP configuration options to allow TX and RX of
zero checksums in IPv6. Default is not to use them.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/l2tp.h

@@ -124,6 +124,8 @@ enum {
 	L2TP_ATTR_STATS,		/* nested */
 	L2TP_ATTR_IP6_SADDR,		/* struct in6_addr */
 	L2TP_ATTR_IP6_DADDR,		/* struct in6_addr */
+	L2TP_ATTR_UDP_ZERO_CSUM6_TX,	/* u8 */
+	L2TP_ATTR_UDP_ZERO_CSUM6_RX,	/* u8 */
 	__L2TP_ATTR_MAX,
 };
 

net/l2tp/l2tp_core.c

@@ -1102,7 +1102,9 @@ static void l2tp_xmit_ipv6_csum(struct sock *sk, struct sk_buff *skb,
 	struct ipv6_pinfo *np = inet6_sk(sk);
 	struct udphdr *uh = udp_hdr(skb);
 
-	if (!skb_dst(skb) || !skb_dst(skb)->dev ||
+	if (udp_get_no_check6_tx(sk))
+		skb->ip_summed = CHECKSUM_NONE;
+	else if (!skb_dst(skb) || !skb_dst(skb)->dev ||
 	    !(skb_dst(skb)->dev->features & NETIF_F_IPV6_CSUM)) {
 		__wsum csum = skb_checksum(skb, 0, udp_len, 0);
 		skb->ip_summed = CHECKSUM_UNNECESSARY;
@@ -1435,6 +1437,11 @@ static int l2tp_tunnel_sock_create(struct net *net,
 					     sizeof(udp6_addr), 0);
 			if (err < 0)
 				goto out;
+
+			if (cfg->udp6_zero_tx_checksums)
+				udp_set_no_check6_tx(sock->sk, true);
+			if (cfg->udp6_zero_rx_checksums)
+				udp_set_no_check6_rx(sock->sk, true);
 		} else
 #endif
 		{

net/l2tp/l2tp_core.h

@@ -162,7 +162,9 @@ struct l2tp_tunnel_cfg {
 #endif
 	u16			local_udp_port;
 	u16			peer_udp_port;
-	unsigned int		use_udp_checksums:1;
+	unsigned int		use_udp_checksums:1,
+				udp6_zero_tx_checksums:1,
+				udp6_zero_rx_checksums:1;
 };
 
 struct l2tp_tunnel {

net/l2tp/l2tp_netlink.c

@@ -161,6 +161,13 @@ static int l2tp_nl_cmd_tunnel_create(struct sk_buff *skb, struct genl_info *info
 			cfg.peer_udp_port = nla_get_u16(info->attrs[L2TP_ATTR_UDP_DPORT]);
 		if (info->attrs[L2TP_ATTR_UDP_CSUM])
 			cfg.use_udp_checksums = nla_get_flag(info->attrs[L2TP_ATTR_UDP_CSUM]);
+
+#if IS_ENABLED(CONFIG_IPV6)
+		if (info->attrs[L2TP_ATTR_UDP_ZERO_CSUM6_TX])
+			cfg.udp6_zero_tx_checksums = nla_get_flag(info->attrs[L2TP_ATTR_UDP_ZERO_CSUM6_TX]);
+		if (info->attrs[L2TP_ATTR_UDP_ZERO_CSUM6_RX])
+			cfg.udp6_zero_rx_checksums = nla_get_flag(info->attrs[L2TP_ATTR_UDP_ZERO_CSUM6_RX]);
+#endif
 	}
 
 	if (info->attrs[L2TP_ATTR_DEBUG])