bpf: sockmap: Only check ULP for TCP sockets

The sock map code checks that a socket does not have an active upper
layer protocol before inserting it into the map. This requires casting
via inet_csk, which isn't valid for UDP sockets.

Guard checks for ULP by checking inet_sk(sk)->is_icsk first.

Signed-off-by: Lorenz Bauer <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Reviewed-by: Jakub Sitnicki <[e-mail]>
Acked-by: John Fastabend <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

include/linux/skmsg.h

···
 					  struct sk_psock *psock)
 {
 	sk->sk_prot->unhash = psock->saved_unhash;
-	tcp_update_ulp(sk, psock->sk_proto, psock->saved_write_space);
+	if (inet_csk_has_ulp(sk)) {
+		tcp_update_ulp(sk, psock->sk_proto, psock->saved_write_space);
+	} else {
+		sk->sk_write_space = psock->saved_write_space;
+		/* Pairs with lockless read in sk_clone_lock() */
+		WRITE_ONCE(sk->sk_prot, psock->sk_proto);
+	}
 }
 
 static inline void sk_psock_set_state(struct sk_psock *psock,

include/net/inet_connection_sock.h

···
 	if (icsk->icsk_ack.pingpong < U8_MAX)
 		icsk->icsk_ack.pingpong++;
 }
+
+static inline bool inet_csk_has_ulp(struct sock *sk)
+{
+	return inet_sk(sk)->is_icsk && !!inet_csk(sk)->icsk_ulp_ops;
+}
+
 #endif /* _INET_CONNECTION_SOCK_H */

net/core/sock_map.c

···
 				  struct sock *sk, u64 flags)
 {
 	struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
-	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct sk_psock_link *link;
 	struct sk_psock *psock;
 	struct sock *osk;
···
 		return -EINVAL;
 	if (unlikely(idx >= map->max_entries))
 		return -E2BIG;
-	if (unlikely(rcu_access_pointer(icsk->icsk_ulp_data)))
+	if (inet_csk_has_ulp(sk))
 		return -EINVAL;
 
 	link = sk_psock_init_link();
···
 				   struct sock *sk, u64 flags)
 {
 	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
-	struct inet_connection_sock *icsk = inet_csk(sk);
 	u32 key_size = map->key_size, hash;
 	struct bpf_htab_elem *elem, *elem_new;
 	struct bpf_htab_bucket *bucket;
···
 	WARN_ON_ONCE(!rcu_read_lock_held());
 	if (unlikely(flags > BPF_EXIST))
 		return -EINVAL;
-	if (unlikely(icsk->icsk_ulp_data))
+	if (inet_csk_has_ulp(sk))
 		return -EINVAL;
 
 	link = sk_psock_init_link();

net/ipv4/tcp_ulp.c

···
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 
-	if (!icsk->icsk_ulp_ops) {
-		sk->sk_write_space = write_space;
-		/* Pairs with lockless read in sk_clone_lock() */
-		WRITE_ONCE(sk->sk_prot, proto);
-		return;
-	}
-
 	if (icsk->icsk_ulp_ops->update)
 		icsk->icsk_ulp_ops->update(sk, proto, write_space);
 }