skmsg: introduce sk_psock_get_checked()

Although we have sk_psock_get(), it assumes the psock
retrieved from sk_user_data is for sockmap, this is not
sufficient if we call it outside of sockmap, for example,
reuseport_array.

Fortunately sock_map_psock_get_checked() is more strict
and checks for sock_map_close before using psock. So we can
refactor it and rename it to sk_psock_get_checked(), which
can be safely called outside of sockmap.

Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jakub Sitnicki <jakub@cloudflare.com>
Cc: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>

include/linux/skmsg.h

@@ -452,6 +452,26 @@ static inline struct sk_psock *sk_psock_get(struct sock *sk)
 	return psock;
 }
 
+static inline struct sk_psock *sk_psock_get_checked(struct sock *sk)
+{
+	struct sk_psock *psock;
+
+	rcu_read_lock();
+	psock = sk_psock(sk);
+	if (psock) {
+		if (sk->sk_prot->close != sock_map_close) {
+			psock = ERR_PTR(-EBUSY);
+			goto out;
+		}
+
+		if (!refcount_inc_not_zero(&psock->refcnt))
+			psock = ERR_PTR(-EBUSY);
+	}
+out:
+	rcu_read_unlock();
+	return psock;
+}
+
 void sk_psock_drop(struct sock *sk, struct sk_psock *psock);
 
 static inline void sk_psock_put(struct sock *sk, struct sk_psock *psock)

net/core/sock_map.c

@@ -191,26 +191,6 @@ static int sock_map_init_proto(struct sock *sk, struct sk_psock *psock)
 	return sk->sk_prot->psock_update_sk_prot(sk, psock, false);
 }
 
-static struct sk_psock *sock_map_psock_get_checked(struct sock *sk)
-{
-	struct sk_psock *psock;
-
-	rcu_read_lock();
-	psock = sk_psock(sk);
-	if (psock) {
-		if (sk->sk_prot->close != sock_map_close) {
-			psock = ERR_PTR(-EBUSY);
-			goto out;
-		}
-
-		if (!refcount_inc_not_zero(&psock->refcnt))
-			psock = ERR_PTR(-EBUSY);
-	}
-out:
-	rcu_read_unlock();
-	return psock;
-}
-
 static int sock_map_link(struct bpf_map *map, struct sock *sk)
 {
 	struct sk_psock_progs *progs = sock_map_progs(map);
@@ -255,7 +235,7 @@ static int sock_map_link(struct bpf_map *map, struct sock *sk)
 		}
 	}
 
-	psock = sock_map_psock_get_checked(sk);
+	psock = sk_psock_get_checked(sk);
 	if (IS_ERR(psock)) {
 		ret = PTR_ERR(psock);
 		goto out_progs;