bpf: sockmap: Simplify sock_map_init_proto

We can take advantage of the fact that both callers of
sock_map_init_proto are holding a RCU read lock, and
have verified that psock is valid.
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200309111243.6982-7-lmb@cloudflare.com

net/core/sock_map.c

@@ -141,28 +141,17 @@ static void sock_map_unref(struct sock *sk, void *link_raw)
 	}
 }
 
-static int sock_map_init_proto(struct sock *sk)
+static int sock_map_init_proto(struct sock *sk, struct sk_psock *psock)
 {
-	struct sk_psock *psock;
 	struct proto *prot;
 
 	sock_owned_by_me(sk);
 
-	rcu_read_lock();
-	psock = sk_psock(sk);
-	if (unlikely(!psock)) {
-		rcu_read_unlock();
-		return -EINVAL;
-	}
-
 	prot = tcp_bpf_get_proto(sk, psock);
-	if (IS_ERR(prot)) {
-		rcu_read_unlock();
+	if (IS_ERR(prot))
 		return PTR_ERR(prot);
-	}
 
 	sk_psock_update_proto(sk, psock, prot);
-	rcu_read_unlock();
 	return 0;
 }
 
@@ -241,7 +230,7 @@ static int sock_map_link(struct bpf_map *map, struct sk_psock_progs *progs,
 	if (msg_parser)
 		psock_set_prog(&psock->progs.msg_parser, msg_parser);
 
-	ret = sock_map_init_proto(sk);
+	ret = sock_map_init_proto(sk, psock);
 	if (ret < 0)
 		goto out_drop;
 
@@ -286,7 +275,7 @@ static int sock_map_link_no_progs(struct bpf_map *map, struct sock *sk)
 			return -ENOMEM;
 	}
 
-	ret = sock_map_init_proto(sk);
+	ret = sock_map_init_proto(sk, psock);
 	if (ret < 0)
 		sk_psock_put(sk, psock);
 	return ret;