USB: oti6858: fix use-after-free in TIOCMIWAIT

commit 8edfdab3 upstream.

Use the port wait queue and make sure to check the serial disconnected
flag before accessing private port data after waking up.

This is is needed as the private port data (including the wait queue
itself) can be gone when waking up after a disconnect.
Signed-off-by: Johan Hovold <jhovold@gmail.com>
[bwh: Backported to 3.2: adjust context, indentation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/oti6858.c

@@ -198,7 +198,6 @@ struct oti6858_private {
 	u8 setup_done;
 	struct delayed_work delayed_setup_work;
 
-	wait_queue_head_t intr_wait;
 	struct usb_serial_port *port;   /* USB port with which associated */
 };
 
@@ -356,7 +355,6 @@ static int oti6858_startup(struct usb_serial *serial)
 			break;
 
 		spin_lock_init(&priv->lock);
-		init_waitqueue_head(&priv->intr_wait);
 /*		INIT_WORK(&priv->setup_work, setup_line, serial->port[i]); */
 /*		INIT_WORK(&priv->write_work, send_data, serial->port[i]); */
 		priv->port = port;
@@ -703,11 +701,15 @@ static int wait_modem_info(struct usb_serial_port *port, unsigned int arg)
 	spin_unlock_irqrestore(&priv->lock, flags);
 
 	while (1) {
-		wait_event_interruptible(priv->intr_wait,
+		wait_event_interruptible(port->delta_msr_wait,
+					port->serial->disconnected ||
 					priv->status.pin_state != prev);
 		if (signal_pending(current))
 			return -ERESTARTSYS;
 
+		if (port->serial->disconnected)
+			return -EIO;
+
 		spin_lock_irqsave(&priv->lock, flags);
 		status = priv->status.pin_state & PIN_MASK;
 		spin_unlock_irqrestore(&priv->lock, flags);
@@ -819,7 +821,7 @@ static void oti6858_read_int_callback(struct urb *urb)
 
 		if (!priv->transient) {
 			if (xs->pin_state != priv->status.pin_state)
-				wake_up_interruptible(&priv->intr_wait);
+				wake_up_interruptible(&port->delta_msr_wait);
 			memcpy(&priv->status, xs, OTI6858_CTRL_PKT_SIZE);
 		}