udptunnel: Add SKB_GSO_UDP_TUNNEL during gro_complete.

When doing GRO processing for UDP tunnels, we never add
SKB_GSO_UDP_TUNNEL to gso_type - only the type of the inner protocol
is added (such as SKB_GSO_TCPV4). The result is that if the packet is
later resegmented we will do GSO but not treat it as a tunnel. This
results in UDP fragmentation of the outer header instead of (i.e.) TCP
segmentation of the inner header as was originally on the wire.
Signed-off-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/vxlan.c

@@ -621,6 +621,8 @@ static int vxlan_gro_complete(struct sk_buff *skb, int nhoff)
 	int vxlan_len  = sizeof(struct vxlanhdr) + sizeof(struct ethhdr);
 	int err = -ENOSYS;
 
+	udp_tunnel_gro_complete(skb, nhoff);
+
 	eh = (struct ethhdr *)(skb->data + nhoff + sizeof(struct vxlanhdr));
 	type = eh->h_proto;
 

include/net/udp_tunnel.h

@@ -100,6 +100,15 @@ static inline struct sk_buff *udp_tunnel_handle_offloads(struct sk_buff *skb,
 	return iptunnel_handle_offloads(skb, udp_csum, type);
 }
 
+static inline void udp_tunnel_gro_complete(struct sk_buff *skb, int nhoff)
+{
+	struct udphdr *uh;
+
+	uh = (struct udphdr *)(skb->data + nhoff - sizeof(struct udphdr));
+	skb_shinfo(skb)->gso_type |= uh->check ?
+				SKB_GSO_UDP_TUNNEL_CSUM : SKB_GSO_UDP_TUNNEL;
+}
+
 static inline void udp_tunnel_encap_enable(struct socket *sock)
 {
 #if IS_ENABLED(CONFIG_IPV6)

net/ipv4/fou.c

@@ -133,6 +133,8 @@ static int fou_gro_complete(struct sk_buff *skb, int nhoff)
 	int err = -ENOSYS;
 	const struct net_offload **offloads;
 
+	udp_tunnel_gro_complete(skb, nhoff);
+
 	rcu_read_lock();
 	offloads = NAPI_GRO_CB(skb)->is_ipv6 ? inet6_offloads : inet_offloads;
 	ops = rcu_dereference(offloads[proto]);