[PATCH v3] net/rose: Fix to not accept on connected socket

[Hyunwoo Kim <v4bel@theori.io>]

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.

Signed-off-by: Hyunwoo Kim <v4bel@theori.io>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
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(+)

diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c
index 36fefc3957d7..ca2b17f32670 100644
--- a/net/rose/af_rose.c
+++ b/net/rose/af_rose.c
@@ -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