ksmbd: add max connections parameter

Add max connections parameter to limit number of maximum simultaneous
connections.

Fixes: 0626e664 ("cifsd: add server handler for central processing and tranport layers")
Cc: stable@vger.kernel.org
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/ksmbd/ksmbd_netlink.h

@@ -106,7 +106,8 @@ struct ksmbd_startup_request {
 	__u32	sub_auth[3];		/* Subauth value for Security ID */
 	__u32	smb2_max_credits;	/* MAX credits */
 	__u32	smbd_max_io_size;	/* smbd read write size */
-	__u32	reserved[127];		/* Reserved room */
+	__u32	max_connections;	/* Number of maximum simultaneous connections */
+	__u32	reserved[126];		/* Reserved room */
 	__u32	ifc_list_sz;		/* interfaces list size */
 	__s8	____payload[];
 };

fs/ksmbd/server.h

@@ -41,6 +41,7 @@ struct ksmbd_server_config {
 	unsigned int		share_fake_fscaps;
 	struct smb_sid		domain_sid;
 	unsigned int		auth_mechs;
+	unsigned int		max_connections;
 
 	char			*conf[SERVER_CONF_WORK_GROUP + 1];
 };

fs/ksmbd/transport_ipc.c

@@ -308,6 +308,9 @@ static int ipc_server_config_on_startup(struct ksmbd_startup_request *req)
 	if (req->smbd_max_io_size)
 		init_smbd_max_io_size(req->smbd_max_io_size);
 
+	if (req->max_connections)
+		server_conf.max_connections = req->max_connections;
+
 	ret = ksmbd_set_netbios_name(req->netbios_name);
 	ret |= ksmbd_set_server_string(req->server_string);
 	ret |= ksmbd_set_work_group(req->work_group);

fs/ksmbd/transport_tcp.c

@@ -15,6 +15,8 @@
 #define IFACE_STATE_DOWN		BIT(0)
 #define IFACE_STATE_CONFIGURED		BIT(1)
 
+static atomic_t active_num_conn;
+
 struct interface {
 	struct task_struct	*ksmbd_kthread;
 	struct socket		*ksmbd_socket;
@@ -185,8 +187,10 @@ static int ksmbd_tcp_new_connection(struct socket *client_sk)
 	struct tcp_transport *t;
 
 	t = alloc_transport(client_sk);
-	if (!t)
+	if (!t) {
+		sock_release(client_sk);
 		return -ENOMEM;
+	}
 
 	csin = KSMBD_TCP_PEER_SOCKADDR(KSMBD_TRANS(t)->conn);
 	if (kernel_getpeername(client_sk, csin) < 0) {
@@ -239,6 +243,15 @@ static int ksmbd_kthread_fn(void *p)
 			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",
+					    atomic_read(&active_num_conn));
+			atomic_dec(&active_num_conn);
+			sock_release(client_sk);
+			continue;
+		}
+
 		ksmbd_debug(CONN, "connect success: accepted new connection\n");
 		client_sk->sk->sk_rcvtimeo = KSMBD_TCP_RECV_TIMEOUT;
 		client_sk->sk->sk_sndtimeo = KSMBD_TCP_SEND_TIMEOUT;
@@ -368,6 +381,8 @@ static int ksmbd_tcp_writev(struct ksmbd_transport *t, struct kvec *iov,
 static void ksmbd_tcp_disconnect(struct ksmbd_transport *t)
 {
 	free_transport(TCP_TRANS(t));
+	if (server_conf.max_connections)
+		atomic_dec(&active_num_conn);
 }
 
 static void tcp_destroy_socket(struct socket *ksmbd_socket)