net/rose: Fix to not accept on connected socket

If you call listen() and accept() on an already connect()ed rose socket, accept() can successfully connect. This is because when the peer socket sends data to sendmsg, the skb with its own sk stored in the connected socket's sk->sk_receive_queue is connected, and rose_accept() dequeues the skb waiting in the sk->sk_receive_queue.

This creates a child socket with the sk of the parent rose socket, which can cause confusion.

Fix rose_listen() to return -EINVAL if the socket has already been successfully connected, and add lock_sock to prevent this issue.

---
v1 -> v2 : Change the flag to check to SS_UNCONNECTED v2 -> v3 : Fix wrong patch description

---
 net/rose/af_rose.c | 8 ++++++++
 1 file changed, 8 insertions(+)

index 36fefc3957d7..ca2b17f32670 100644
@@ -488,6 +488,12 @@ static int rose_listen(struct socket *sock, int backlog)
 {
 	struct sock *sk = sock->sk;
 
+	lock_sock(sk);
+	if (sock->state != SS_UNCONNECTED) {
+		release_sock(sk);
+		return -EINVAL;
+	}
+
 	if (sk->sk_state != TCP_LISTEN) {
 		struct rose_sock *rose = rose_sk(sk);
 

@@ -497,8 +503,10 @@ static int rose_listen(struct socket *sock, int backlog)
 		memset(rose->dest_digis, 0, AX25_ADDR_LEN * ROSE_MAX_DIGIS);
 		sk->sk_max_ack_backlog = backlog;
 		sk->sk_state           = TCP_LISTEN;
+		release_sock(sk);
 		return 0;
 	}
+	release_sock(sk);
 
 	return -EOPNOTSUPP;
 }

2.25.1