USB: ftdi_sio: 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.

When switching to tty ports, some lifetime assumptions were changed.
Specifically, close can now be called before the final tty reference is
dropped as part of hangup at device disconnect. Even with the ftdi
private-data refcounting this means that the port private data can be
freed while a process is sleeping on modem-status changes and thus
cannot be relied on to detect disconnects when woken up.

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/ftdi_sio.c

@@ -69,9 +69,7 @@ struct ftdi_private {
 	int flags;		/* some ASYNC_xxxx flags are supported */
 	unsigned long last_dtr_rts;	/* saved modem control outputs */
 	struct async_icount	icount;
-	wait_queue_head_t delta_msr_wait; /* Used for TIOCMIWAIT */
 	char prev_status;        /* Used for TIOCMIWAIT */
-	bool dev_gone;        /* Used to abort TIOCMIWAIT */
 	char transmit_empty;	/* If transmitter is empty or not */
 	__u16 interface;	/* FT2232C, FT2232H or FT4232H port interface
 				   (0 for FT232/245) */
@@ -1691,10 +1689,8 @@ static int ftdi_sio_port_probe(struct usb_serial_port *port)
 
 	kref_init(&priv->kref);
 	mutex_init(&priv->cfg_lock);
-	init_waitqueue_head(&priv->delta_msr_wait);
 
 	priv->flags = ASYNC_LOW_LATENCY;
-	priv->dev_gone = false;
 
 	if (quirk && quirk->port_probe)
 		quirk->port_probe(priv);
@@ -1840,8 +1836,7 @@ static int ftdi_sio_port_remove(struct usb_serial_port *port)
 {
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
 
-	priv->dev_gone = true;
-	wake_up_interruptible_all(&priv->delta_msr_wait);
+	wake_up_interruptible(&port->delta_msr_wait);
 
 	remove_sysfs_attrs(port);
 
@@ -1989,7 +1984,7 @@ static int ftdi_process_packet(struct usb_serial_port *port,
 		if (diff_status & FTDI_RS0_RLSD)
 			priv->icount.dcd++;
 
-		wake_up_interruptible_all(&priv->delta_msr_wait);
+		wake_up_interruptible(&port->delta_msr_wait);
 		priv->prev_status = status;
 	}
 
@@ -2440,11 +2435,15 @@ static int ftdi_ioctl(struct tty_struct *tty,
 	 */
 	case TIOCMIWAIT:
 		cprev = priv->icount;
-		while (!priv->dev_gone) {
-			interruptible_sleep_on(&priv->delta_msr_wait);
+		for (;;) {
+			interruptible_sleep_on(&port->delta_msr_wait);
 			/* see if a signal did it */
 			if (signal_pending(current))
 				return -ERESTARTSYS;
+
+			if (port->serial->disconnected)
+				return -EIO;
+
 			cnow = priv->icount;
 			if (((arg & TIOCM_RNG) && (cnow.rng != cprev.rng)) ||
 			    ((arg & TIOCM_DSR) && (cnow.dsr != cprev.dsr)) ||
@@ -2454,8 +2453,6 @@ static int ftdi_ioctl(struct tty_struct *tty,
 			}
 			cprev = cnow;
 		}
-		return -EIO;
-		break;
 	case TIOCSERGETLSR:
 		return get_lsr_info(port, (struct serial_struct __user *)arg);
 		break;