Input: mousedev - fix race when creating mixed device

We should not be using static variable mousedev_mix in methods that can be
called before that singleton gets assigned. While at it let's add open and
close methods to mousedev structure so that we do not need to test if we
are dealing with multiplexor or normal device and simply call appropriate
method directly.

This fixes: https://bugzilla.kernel.org/show_bug.cgi?id=71551

Reported-by: GiulioDP <[e-mail]>
Tested-by: GiulioDP <[e-mail]>
Cc: [e-mail]
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/mousedev.c

···
 	struct device dev;
 	struct cdev cdev;
 	bool exist;
-	bool is_mixdev;
 
 	struct list_head mixdev_node;
 	bool opened_by_mixdev;
···
 	int old_x[4], old_y[4];
 	int frac_dx, frac_dy;
 	unsigned long touch;
+
+	int (*open_device)(struct mousedev *mousedev);
+	void (*close_device)(struct mousedev *mousedev);
 };
 
 enum mousedev_emul {
···
 
 static struct mousedev *mousedev_mix;
 static LIST_HEAD(mousedev_mix_list);
-
-static void mixdev_open_devices(void);
-static void mixdev_close_devices(void);
 
 #define fx(i)  (mousedev->old_x[(mousedev->pkt_count - (i)) & 03])
 #define fy(i)  (mousedev->old_y[(mousedev->pkt_count - (i)) & 03])
···
 	if (retval)
 		return retval;
 
-	if (mousedev->is_mixdev)
-		mixdev_open_devices();
-	else if (!mousedev->exist)
+	if (!mousedev->exist)
 		retval = -ENODEV;
 	else if (!mousedev->open++) {
 		retval = input_open_device(&mousedev->handle);
···
 {
 	mutex_lock(&mousedev->mutex);
 
-	if (mousedev->is_mixdev)
-		mixdev_close_devices();
-	else if (mousedev->exist && !--mousedev->open)
+	if (mousedev->exist && !--mousedev->open)
 		input_close_device(&mousedev->handle);
 
 	mutex_unlock(&mousedev->mutex);
···
  * stream. Note that this function is called with mousedev_mix->mutex
  * held.
  */
-static void mixdev_open_devices(void)
+static int mixdev_open_devices(struct mousedev *mixdev)
 {
-	struct mousedev *mousedev;
+	int error;
 
-	if (mousedev_mix->open++)
-		return;
+	error = mutex_lock_interruptible(&mixdev->mutex);
+	if (error)
+		return error;
 
-	list_for_each_entry(mousedev, &mousedev_mix_list, mixdev_node) {
-		if (!mousedev->opened_by_mixdev) {
-			if (mousedev_open_device(mousedev))
-				continue;
+	if (!mixdev->open++) {
+		struct mousedev *mousedev;
 
-			mousedev->opened_by_mixdev = true;
+		list_for_each_entry(mousedev, &mousedev_mix_list, mixdev_node) {
+			if (!mousedev->opened_by_mixdev) {
+				if (mousedev_open_device(mousedev))
+					continue;
+
+				mousedev->opened_by_mixdev = true;
+			}
 		}
 	}
+
+	mutex_unlock(&mixdev->mutex);
+	return 0;
 }
 
 /*
···
  * device. Note that this function is called with mousedev_mix->mutex
  * held.
  */
-static void mixdev_close_devices(void)
+static void mixdev_close_devices(struct mousedev *mixdev)
 {
-	struct mousedev *mousedev;
+	mutex_lock(&mixdev->mutex);
 
-	if (--mousedev_mix->open)
-		return;
+	if (!--mixdev->open) {
+		struct mousedev *mousedev;
 
-	list_for_each_entry(mousedev, &mousedev_mix_list, mixdev_node) {
-		if (mousedev->opened_by_mixdev) {
-			mousedev->opened_by_mixdev = false;
-			mousedev_close_device(mousedev);
+		list_for_each_entry(mousedev, &mousedev_mix_list, mixdev_node) {
+			if (mousedev->opened_by_mixdev) {
+				mousedev->opened_by_mixdev = false;
+				mousedev_close_device(mousedev);
+			}
 		}
 	}
+
+	mutex_unlock(&mixdev->mutex);
 }
 
 
···
 	mousedev_detach_client(mousedev, client);
 	kfree(client);
 
-	mousedev_close_device(mousedev);
+	mousedev->close_device(mousedev);
 
 	return 0;
 }
···
 	client->mousedev = mousedev;
 	mousedev_attach_client(mousedev, client);
 
-	error = mousedev_open_device(mousedev);
+	error = mousedev->open_device(mousedev);
 	if (error)
 		goto err_free_client;
 
···
 
 	if (mixdev) {
 		dev_set_name(&mousedev->dev, "mice");
+
+		mousedev->open_device = mixdev_open_devices;
+		mousedev->close_device = mixdev_close_devices;
 	} else {
 		int dev_no = minor;
 		/* Normalize device number if it falls into legacy range */
 		if (dev_no < MOUSEDEV_MINOR_BASE + MOUSEDEV_MINORS)
 			dev_no -= MOUSEDEV_MINOR_BASE;
 		dev_set_name(&mousedev->dev, "mouse%d", dev_no);
+
+		mousedev->open_device = mousedev_open_device;
+		mousedev->close_device = mousedev_close_device;
 	}
 
 	mousedev->exist = true;
-	mousedev->is_mixdev = mixdev;
 	mousedev->handle.dev = input_get_device(dev);
 	mousedev->handle.name = dev_name(&mousedev->dev);
 	mousedev->handle.handler = handler;
···
 	device_del(&mousedev->dev);
 	mousedev_cleanup(mousedev);
 	input_free_minor(MINOR(mousedev->dev.devt));
-	if (!mousedev->is_mixdev)
+	if (mousedev != mousedev_mix)
 		input_unregister_handle(&mousedev->handle);
 	put_device(&mousedev->dev);
 }