fou: clean up socket with kfree_rcu

fou->udp_offloads is managed by RCU. As it is actually included inside
the fou sockets, we cannot let the memory go out of scope before a grace
period. We either can synchronize_rcu or switch over to kfree_rcu to
manage the sockets. kfree_rcu seems appropriate as it is used by vxlan
and geneve.

Fixes: 23461551 ("fou: Support for foo-over-udp RX path")
Cc: Tom Herbert <tom@herbertland.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fou.c

@@ -24,6 +24,7 @@ struct fou {
 	u16 type;
 	struct udp_offload udp_offloads;
 	struct list_head list;
+	struct rcu_head rcu;
 };
 
 #define FOU_F_REMCSUM_NOPARTIAL BIT(0)
@@ -417,7 +418,7 @@ static void fou_release(struct fou *fou)
 	list_del(&fou->list);
 	udp_tunnel_sock_release(sock);
 
-	kfree(fou);
+	kfree_rcu(fou, rcu);
 }
 
 static int fou_encap_init(struct sock *sk, struct fou *fou, struct fou_cfg *cfg)