ksmbd: limit repeated connections from clients with the same IP

Repeated connections from clients with the same IP address may exhaust
the max connections and prevent other normal client connections.
This patch limit repeated connections from clients with the same IP.

Reported-by: tianshuo han <hantianshuo233@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: namjaejeon

fs/smb/server/connection.h

@@ -46,6 +46,7 @@ struct ksmbd_conn {
 	struct mutex			srv_mutex;
 	int				status;
 	unsigned int			cli_cap;
+	__be32				inet_addr;
 	char				*request_buf;
 	struct ksmbd_transport		*transport;
 	struct nls_table		*local_nls;

fs/smb/server/transport_tcp.c

@@ -87,6 +87,7 @@ static struct tcp_transport *alloc_transport(struct socket *client_sk)
 		return NULL;
 	}
 
+	conn->inet_addr = inet_sk(client_sk->sk)->inet_daddr;
 	conn->transport = KSMBD_TRANS(t);
 	KSMBD_TRANS(t)->conn = conn;
 	KSMBD_TRANS(t)->ops = &ksmbd_tcp_transport_ops;
@@ -230,6 +231,8 @@ static int ksmbd_kthread_fn(void *p)
 {
 	struct socket *client_sk = NULL;
 	struct interface *iface = (struct interface *)p;
+	struct inet_sock *csk_inet;
+	struct ksmbd_conn *conn;
 	int ret;
 
 	while (!kthread_should_stop()) {
@@ -248,6 +251,20 @@ static int ksmbd_kthread_fn(void *p)
 			continue;
 		}
 
+		/*
+		 * Limits repeated connections from clients with the same IP.
+		 */
+		csk_inet = inet_sk(client_sk->sk);
+		down_read(&conn_list_lock);
+		list_for_each_entry(conn, &conn_list, conns_list)
+			if (csk_inet->inet_daddr == conn->inet_addr) {
+				ret = -EAGAIN;
+				break;
+			}
+		up_read(&conn_list_lock);
+		if (ret == -EAGAIN)
+			continue;
+
 		if (server_conf.max_connections &&
 		    atomic_inc_return(&active_num_conn) >= server_conf.max_connections) {
 			pr_info_ratelimited("Limit the maximum number of connections(%u)\n",