Input: evdev - call input_flush_device() on release(), not flush()

input_flush_device() should only be called once the struct file is being
released and no open descriptors remain, but evdev_flush() was calling
it whenever a file descriptor was closed.

This caused uploaded force-feedback effects to be erased when a process
did a dup()/close() on the event FD, called system(), etc.

Call input_flush_device() from evdev_release() instead.
Reported-by: Mathieu Maret <mathieu.maret@gmail.com>
Signed-off-by: Brendan Shanks <bshanks@codeweavers.com>
Link: https://lore.kernel.org/r/20200421231003.7935-1-bshanks@codeweavers.com
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/evdev.c

@@ -326,20 +326,6 @@ static int evdev_fasync(int fd, struct file *file, int on)
 	return fasync_helper(fd, file, on, &client->fasync);
 }
 
-static int evdev_flush(struct file *file, fl_owner_t id)
-{
-	struct evdev_client *client = file->private_data;
-	struct evdev *evdev = client->evdev;
-
-	mutex_lock(&evdev->mutex);
-
-	if (evdev->exist && !client->revoked)
-		input_flush_device(&evdev->handle, file);
-
-	mutex_unlock(&evdev->mutex);
-	return 0;
-}
-
 static void evdev_free(struct device *dev)
 {
 	struct evdev *evdev = container_of(dev, struct evdev, dev);
@@ -453,6 +439,10 @@ static int evdev_release(struct inode *inode, struct file *file)
 	unsigned int i;
 
 	mutex_lock(&evdev->mutex);
+
+	if (evdev->exist && !client->revoked)
+		input_flush_device(&evdev->handle, file);
+
 	evdev_ungrab(evdev, client);
 	mutex_unlock(&evdev->mutex);
 
@@ -1310,7 +1300,6 @@ static const struct file_operations evdev_fops = {
 	.compat_ioctl	= evdev_ioctl_compat,
 #endif
 	.fasync		= evdev_fasync,
-	.flush		= evdev_flush,
 	.llseek		= no_llseek,
 };