When listen() and accept() are called on an x25 socket
that connect() succeeds, accept() succeeds immediately.
This is because x25_connect() queues the skb to
sk->sk_receive_queue, and x25_accept() dequeues it.

This creates a child socket with the sk of the parent
x25 socket, which can cause confusion.

Fix x25_listen() to return -EINVAL if the socket has
already been successfully connect()ed to avoid this issue.

Signed-off-by: Hyunwoo Kim <redacted>
---
 net/x25/af_x25.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c
index 3b55502b2965..4407a625daa6 100644
--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c

@@ -482,6 +482,12 @@ static int x25_listen(struct socket *sock, int backlog)
 	int rc = -EOPNOTSUPP;
 
 	lock_sock(sk);
+	if (sock->state == SS_CONNECTED) {
+		rc = -EINVAL;
+		release_sock(sk);
+		return rc;
+	}
+
 	if (sk->sk_state != TCP_LISTEN) {
 		memset(&x25_sk(sk)->dest_addr, 0, X25_ADDR_LEN);
 		sk->sk_max_ack_backlog = backlog;

-- 
2.25.1