driver: platform: Add helper for safer setting of driver_override

index 4eabfe28d2b39..9fb57df44c77b 100644
@@ -31,6 +31,75 @@ static struct device *next_device(struct klist_iter *i)
 	return dev;
 }
 
+/**
+ * driver_set_override() - Helper to set or clear driver override.
+ * @dev: Device to change
+ * @override: Address of string to change (e.g. &device->driver_override);
+ *            The contents will be freed and hold newly allocated override.
+ * @s: NUL-terminated string, new driver name to force a match, pass empty
+ *     string to clear it ("" or "\n", where the latter is only for sysfs
+ *     interface).
+ * @len: length of @s
+ *
+ * Helper to set or clear driver override in a device, intended for the cases
+ * when the driver_override field is allocated by driver/bus code.
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+int driver_set_override(struct device *dev, const char **override,
+			const char *s, size_t len)
+{
+	const char *new, *old;
+	char *cp;
+
+	if (!override || !s)
+		return -EINVAL;
+
+	/*
+	 * The stored value will be used in sysfs show callback (sysfs_emit()),
+	 * which has a length limit of PAGE_SIZE and adds a trailing newline.
+	 * Thus we can store one character less to avoid truncation during sysfs
+	 * show.
+	 */
+	if (len >= (PAGE_SIZE - 1))
+		return -EINVAL;
+
+	if (!len) {
+		/* Empty string passed - clear override */
+		device_lock(dev);
+		old = *override;
+		*override = NULL;
+		device_unlock(dev);
+		kfree(old);
+
+		return 0;
+	}
+
+	cp = strnchr(s, len, '\n');
+	if (cp)
+		len = cp - s;
+
+	new = kstrndup(s, len, GFP_KERNEL);
+	if (!new)
+		return -ENOMEM;
+
+	device_lock(dev);
+	old = *override;
+	if (cp != s) {
+		*override = new;
+	} else {
+		/* "\n" passed - clear override */
+		kfree(new);
+		*override = NULL;
+	}
+	device_unlock(dev);
+
+	kfree(old);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(driver_set_override);
+
 /**
  * driver_for_each_device - Iterator for devices bound to a driver.
  * @drv: Driver we're iterating.

index 0ee3cab88f70f..f2273655284f0 100644
@@ -873,31 +873,11 @@ static ssize_t driver_override_store(struct device *dev,
 				     const char *buf, size_t count)
 {
 	struct platform_device *pdev = to_platform_device(dev);
-	char *driver_override, *old, *cp;
-
-	/* We need to keep extra room for a newline */
-	if (count >= (PAGE_SIZE - 1))
-		return -EINVAL;
-
-	driver_override = kstrndup(buf, count, GFP_KERNEL);
-	if (!driver_override)
-		return -ENOMEM;
-
-	cp = strchr(driver_override, '\n');
-	if (cp)
-		*cp = '\0';
-
-	device_lock(dev);
-	old = pdev->driver_override;
-	if (strlen(driver_override)) {
-		pdev->driver_override = driver_override;
-	} else {
-		kfree(driver_override);
-		pdev->driver_override = NULL;
-	}
-	device_unlock(dev);
+	int ret;
 
-	kfree(old);
+	ret = driver_set_override(dev, &pdev->driver_override, buf, count);
+	if (ret)
+		return ret;
 
 	return count;
 }

index fab5798a47fdb..65e06a066b671 100644
@@ -319,6 +319,8 @@ extern int __must_check driver_create_file(struct device_driver *driver,
 extern void driver_remove_file(struct device_driver *driver,
 			       const struct driver_attribute *attr);
 
+int driver_set_override(struct device *dev, const char **override,
+			const char *s, size_t len);
 extern int __must_check driver_for_each_device(struct device_driver *drv,
 					       struct device *start,
 					       void *data,

index 49f634d961188..8fdd3290072b8 100644
@@ -29,7 +29,11 @@ struct platform_device {
 	struct resource	*resource;
 
 	const struct platform_device_id	*id_entry;
-	char *driver_override; /* Driver name to force a match */
+	/*
+	 * Driver name to force a match.  Do not set directly, because core
+	 * frees it.  Use driver_set_override() to set or clear it.
+	 */
+	const char *driver_override;
 
 	/* MFD cell pointer */
 	struct mfd_cell *mfd_cell;

index 0cf9c7e2ee835..e1522caadbc8a 100644
@@ -91,10 +91,19 @@ struct device *rpmsg_find_device(struct device *parent,
  */
 static inline int rpmsg_chrdev_register_device(struct rpmsg_device *rpdev)
 {
+	int ret;
+
 	strcpy(rpdev->id.name, "rpmsg_chrdev");
-	rpdev->driver_override = "rpmsg_chrdev";
+	ret = driver_set_override(&rpdev->dev, &rpdev->driver_override,
+				  rpdev->id.name, strlen(rpdev->id.name));
+	if (ret)
+		return ret;
+
+	ret = rpmsg_register_device(rpdev);
+	if (ret)
+		kfree(rpdev->driver_override);
 
-	return rpmsg_register_device(rpdev);
+	return ret;
 }
 
 #endif

index 1ab79e8dc0b8f..fdbb7814cfbe8 100644
@@ -66,7 +66,9 @@ struct rpmsg_channel_info {
  * rpmsg_device - device that belong to the rpmsg bus
  * @dev: the device struct
  * @id: device id (used to match between rpmsg drivers and devices)
- * @driver_override: driver name to force a match
+ * @driver_override: driver name to force a match; do not set directly,
+ *                   because core frees it; use driver_set_override() to
+ *                   set or clear it.
  * @src: local address
  * @dst: destination address
  * @ept: the rpmsg endpoint of this channel

@@ -75,7 +77,7 @@ struct rpmsg_channel_info {
 struct rpmsg_device {
 	struct device dev;
 	struct rpmsg_device_id id;
-	char *driver_override;
+	const char *driver_override;
 	u32 src;
 	u32 dst;
 	struct rpmsg_endpoint *ept;

index dffa3aab71782..af1a50a799aa8 100644
@@ -474,24 +474,51 @@ static struct bus_type rpmsg_bus = {
 	.remove		= rpmsg_dev_remove,
 };
 
-int rpmsg_register_device(struct rpmsg_device *rpdev)
+/*
+ * A helper for registering rpmsg device with driver override and name.
+ * Drivers should not be using it, but instead rpmsg_register_device().
+ */
+int rpmsg_register_device_override(struct rpmsg_device *rpdev,
+				   const char *driver_override)
 {
 	struct device *dev = &rpdev->dev;
 	int ret;
 
+	if (driver_override)
+		strcpy(rpdev->id.name, driver_override);
+
 	dev_set_name(&rpdev->dev, "%s.%s.%d.%d", dev_name(dev->parent),
 		     rpdev->id.name, rpdev->src, rpdev->dst);
 
 	rpdev->dev.bus = &rpmsg_bus;
 
-	ret = device_register(&rpdev->dev);
+	device_initialize(dev);
+	if (driver_override) {
+		ret = driver_set_override(dev, &rpdev->driver_override,
+					  driver_override,
+					  strlen(driver_override));
+		if (ret) {
+			dev_err(dev, "device_set_override failed: %d\n", ret);
+			return ret;
+		}
+	}
+
+	ret = device_add(dev);
 	if (ret) {
-		dev_err(dev, "device_register failed: %d\n", ret);
+		dev_err(dev, "device_add failed: %d\n", ret);
+		kfree(rpdev->driver_override);
+		rpdev->driver_override = NULL;
 		put_device(&rpdev->dev);
 	}
 
 	return ret;
 }
+EXPORT_SYMBOL(rpmsg_register_device_override);
+
+int rpmsg_register_device(struct rpmsg_device *rpdev)
+{
+	return rpmsg_register_device_override(rpdev, NULL);
+}
 EXPORT_SYMBOL(rpmsg_register_device);
 
 /*

index e1522caadbc8a..868698a3d4c2a 100644
@@ -91,19 +91,7 @@ struct device *rpmsg_find_device(struct device *parent,
  */
 static inline int rpmsg_chrdev_register_device(struct rpmsg_device *rpdev)
 {
-	int ret;
-
-	strcpy(rpdev->id.name, "rpmsg_chrdev");
-	ret = driver_set_override(&rpdev->dev, &rpdev->driver_override,
-				  rpdev->id.name, strlen(rpdev->id.name));
-	if (ret)
-		return ret;
-
-	ret = rpmsg_register_device(rpdev);
-	if (ret)
-		kfree(rpdev->driver_override);
-
-	return ret;
+	return rpmsg_register_device_override(rpdev, "rpmsg_ctrl");
 }
 
 #endif

index fdbb7814cfbe8..650ebbd35b0c3 100644
@@ -140,6 +140,8 @@ struct rpmsg_driver {
 
 #if IS_ENABLED(CONFIG_RPMSG)
 
+int rpmsg_register_device_override(struct rpmsg_device *rpdev,
+				   const char *driver_override);
 int register_rpmsg_device(struct rpmsg_device *dev);
 void unregister_rpmsg_device(struct rpmsg_device *dev);
 int __register_rpmsg_driver(struct rpmsg_driver *drv, struct module *owner);

@@ -164,6 +166,12 @@ unsigned int rpmsg_poll(struct rpmsg_endpoint *ept, struct file *filp,
 
 #else
 
+static inline int rpmsg_register_device_override(struct rpmsg_device *rpdev,
+						 const char *driver_override)
+{
+	return -ENXIO;
+}
+
 static inline int register_rpmsg_device(struct rpmsg_device *dev)
 {
 	return -ENXIO;

index c1dfad2986859..8ee814d6dddce 100644
@@ -1354,6 +1354,7 @@ static void qcom_glink_rpdev_release(struct device *dev)
 	struct glink_channel *channel = to_glink_channel(rpdev->ept);
 
 	channel->rpdev = NULL;
+	kfree(rpdev->driver_override);
 	kfree(rpdev);
 }
 

index af1a50a799aa8..1389a32fdea33 100644
@@ -499,6 +499,7 @@ int rpmsg_register_device_override(struct rpmsg_device *rpdev,
 					  strlen(driver_override));
 		if (ret) {
 			dev_err(dev, "device_set_override failed: %d\n", ret);
+			put_device(dev);
 			return ret;
 		}
 	}