staging: sep: call to sep_ioctl() may leave driver in unusable state

If sep_ioctl() is called from a process that does not own
current transaction, it unlocks unheld sep->ioctl_mutex and
returns -EACCES leaving sep->sep_mutex acquired.

The patch fixes the mutex lock-unlock mismatch.

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/sep/sep_driver.c

@@ -2420,11 +2420,12 @@ static long sep_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 				(sep->pid_doing_transaction != 0)) {
 		dev_dbg(&sep->pdev->dev, "ioctl pid is not owner\n");
 		error = -EACCES;
-		goto end_function;
 	}
-
 	mutex_unlock(&sep->sep_mutex);
 
+	if (error)
+		return error;
+
 	if (_IOC_TYPE(cmd) != SEP_IOC_MAGIC_NUMBER)
 		return -ENOTTY;
 
@@ -2461,7 +2462,6 @@ static long sep_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		break;
 	}
 
-end_function:
 	mutex_unlock(&sep->ioctl_mutex);
 	return error;
 }