hso: Fix crashes on close.

Moved serial_open_count in hso_serial_open to
prevent crashes owing to the serial structure being made NULL
when hso_serial_close is called even though hso_serial_open
returned -ENODEV, Alan Cox pointed out this happens,
also put in sanity check in hso_serial_close
to check for a valid serial structure which should prevent
the most reproducable crash in the driver when the hso device
is disconnected while in use.

Signed-off-by: Denis Joseph Barrow <D.Barow@option.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/hso.c

@@ -1235,6 +1235,11 @@ static int hso_serial_open(struct tty_struct *tty, struct file *filp)
 	}
 
 	mutex_lock(&serial->parent->mutex);
+	/* check for port already opened, if not set the termios */
+	/* The serial->open count needs to be here as hso_serial_close
+	 *  will be called even if hso_serial_open returns -ENODEV.
+	 */
+	serial->open_count++;
 	result = usb_autopm_get_interface(serial->parent->interface);
 	if (result < 0)
 		goto err_out;
@@ -1246,8 +1251,6 @@ static int hso_serial_open(struct tty_struct *tty, struct file *filp)
 	tty->driver_data = serial;
 	serial->tty = tty;
 
-	/* check for port already opened, if not set the termios */
-	serial->open_count++;
 	if (serial->open_count == 1) {
 		tty->low_latency = 1;
 		serial->rx_state = RX_IDLE;
@@ -1285,6 +1288,10 @@ static void hso_serial_close(struct tty_struct *tty, struct file *filp)
 	u8 usb_gone;
 
 	D1("Closing serial port");
+	if (serial == NULL || serial->magic != HSO_SERIAL_MAGIC) {
+		D1("invalid serial structure bailing out.\n");
+		return;
+	}
 
 	mutex_lock(&serial->parent->mutex);
 	usb_gone = serial->parent->usb_gone;