USB: quatech2: fix use-after-free in TIOCMIWAIT

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.

Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/quatech2.c

@@ -128,7 +128,6 @@ struct qt2_port_private {
 	u8          shadowLSR;
 	u8          shadowMSR;
 
-	wait_queue_head_t   delta_msr_wait; /* Used for TIOCMIWAIT */
 	struct async_icount icount;
 
 	struct usb_serial_port *port;
@@ -506,8 +505,9 @@ 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->delta_msr_wait,
-					 ((priv->icount.rng != prev.rng) ||
+		wait_event_interruptible(port->delta_msr_wait,
+					 (port->serial->disconnected ||
+					  (priv->icount.rng != prev.rng) ||
 					  (priv->icount.dsr != prev.dsr) ||
 					  (priv->icount.dcd != prev.dcd) ||
 					  (priv->icount.cts != prev.cts)));
@@ -515,6 +515,9 @@ static int wait_modem_info(struct usb_serial_port *port, unsigned int arg)
 		if (signal_pending(current))
 			return -ERESTARTSYS;
 
+		if (port->serial->disconnected)
+			return -EIO;
+
 		spin_lock_irqsave(&priv->lock, flags);
 		cur = priv->icount;
 		spin_unlock_irqrestore(&priv->lock, flags);
@@ -827,7 +830,6 @@ static int qt2_port_probe(struct usb_serial_port *port)
 
 	spin_lock_init(&port_priv->lock);
 	spin_lock_init(&port_priv->urb_lock);
-	init_waitqueue_head(&port_priv->delta_msr_wait);
 	port_priv->port = port;
 
 	port_priv->write_urb = usb_alloc_urb(0, GFP_KERNEL);
@@ -970,7 +972,7 @@ static void qt2_update_msr(struct usb_serial_port *port, unsigned char *ch)
 		if (newMSR & UART_MSR_TERI)
 			port_priv->icount.rng++;
 
-		wake_up_interruptible(&port_priv->delta_msr_wait);
+		wake_up_interruptible(&port->delta_msr_wait);
 	}
 }