USB: mct_u232: fix use-after-free in TIOCMIWAIT

commit cf1d2444 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]
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/mct_u232.c

@@ -126,8 +126,6 @@ struct mct_u232_private {
 	unsigned char	     last_msr;      /* Modem Status Register */
 	unsigned int	     rx_flags;      /* Throttling flags */
 	struct async_icount  icount;
-	wait_queue_head_t    msr_wait;	/* for handling sleeping while waiting
-						for msr change to happen */
 };
 
 #define THROTTLED		0x01
@@ -407,7 +405,6 @@ static int mct_u232_startup(struct usb_serial *serial)
 	if (!priv)
 		return -ENOMEM;
 	spin_lock_init(&priv->lock);
-	init_waitqueue_head(&priv->msr_wait);
 	usb_set_serial_port_data(serial->port[0], priv);
 
 	init_waitqueue_head(&serial->port[0]->write_wait);
@@ -631,7 +628,7 @@ static void mct_u232_read_int_callback(struct urb *urb)
 		tty_kref_put(tty);
 	}
 #endif
-	wake_up_interruptible(&priv->msr_wait);
+	wake_up_interruptible(&port->delta_msr_wait);
 	spin_unlock_irqrestore(&priv->lock, flags);
 exit:
 	retval = usb_submit_urb(urb, GFP_ATOMIC);
@@ -852,13 +849,17 @@ static int  mct_u232_ioctl(struct tty_struct *tty,
 		cprev = mct_u232_port->icount;
 		spin_unlock_irqrestore(&mct_u232_port->lock, flags);
 		for ( ; ; ) {
-			prepare_to_wait(&mct_u232_port->msr_wait,
+			prepare_to_wait(&port->delta_msr_wait,
 					&wait, TASK_INTERRUPTIBLE);
 			schedule();
-			finish_wait(&mct_u232_port->msr_wait, &wait);
+			finish_wait(&port->delta_msr_wait, &wait);
 			/* see if a signal did it */
 			if (signal_pending(current))
 				return -ERESTARTSYS;
+
+			if (port->serial->disconnected)
+				return -EIO;
+
 			spin_lock_irqsave(&mct_u232_port->lock, flags);
 			cnow = mct_u232_port->icount;
 			spin_unlock_irqrestore(&mct_u232_port->lock, flags);