IB/ucm: utilize new cdev_device_add helper function

The use after free is not triggerable here because the cdev holds
the module lock and the only device_unregister is only triggered by
module unload, however make the change for consistency.

To make this work the cdev_del needs to move out of the struct device
release function.

This cleans up the error path significantly and thus also fixes a minor
bug where the devnum would not be released if cdev_add failed.
Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/infiniband/core/ucm.c

@@ -1205,12 +1205,15 @@ static void ib_ucm_release_dev(struct device *dev)
 	struct ib_ucm_device *ucm_dev;
 
 	ucm_dev = container_of(dev, struct ib_ucm_device, dev);
-	cdev_del(&ucm_dev->cdev);
+	kfree(ucm_dev);
+}
+
+static void ib_ucm_free_dev(struct ib_ucm_device *ucm_dev)
+{
 	if (ucm_dev->devnum < IB_UCM_MAX_DEVICES)
 		clear_bit(ucm_dev->devnum, dev_map);
 	else
 		clear_bit(ucm_dev->devnum - IB_UCM_MAX_DEVICES, overflow_map);
-	kfree(ucm_dev);
 }
 
 static const struct file_operations ucm_fops = {
@@ -1266,7 +1269,9 @@ static void ib_ucm_add_one(struct ib_device *device)
 	if (!ucm_dev)
 		return;
 
+	device_initialize(&ucm_dev->dev);
 	ucm_dev->ib_dev = device;
+	ucm_dev->dev.release = ib_ucm_release_dev;
 
 	devnum = find_first_zero_bit(dev_map, IB_UCM_MAX_DEVICES);
 	if (devnum >= IB_UCM_MAX_DEVICES) {
@@ -1286,16 +1291,14 @@ static void ib_ucm_add_one(struct ib_device *device)
 	cdev_init(&ucm_dev->cdev, &ucm_fops);
 	ucm_dev->cdev.owner = THIS_MODULE;
 	kobject_set_name(&ucm_dev->cdev.kobj, "ucm%d", ucm_dev->devnum);
-	if (cdev_add(&ucm_dev->cdev, base, 1))
-		goto err;
 
 	ucm_dev->dev.class = &cm_class;
 	ucm_dev->dev.parent = device->dev.parent;
-	ucm_dev->dev.devt = ucm_dev->cdev.dev;
-	ucm_dev->dev.release = ib_ucm_release_dev;
+	ucm_dev->dev.devt = base;
+
 	dev_set_name(&ucm_dev->dev, "ucm%d", ucm_dev->devnum);
-	if (device_register(&ucm_dev->dev))
-		goto err_cdev;
+	if (cdev_device_add(&ucm_dev->cdev, &ucm_dev->dev))
+		goto err_devnum;
 
 	if (device_create_file(&ucm_dev->dev, &dev_attr_ibdev))
 		goto err_dev;
@@ -1304,15 +1307,11 @@ static void ib_ucm_add_one(struct ib_device *device)
 	return;
 
 err_dev:
-	device_unregister(&ucm_dev->dev);
-err_cdev:
-	cdev_del(&ucm_dev->cdev);
-	if (ucm_dev->devnum < IB_UCM_MAX_DEVICES)
-		clear_bit(devnum, dev_map);
-	else
-		clear_bit(devnum, overflow_map);
+	cdev_device_del(&ucm_dev->cdev, &ucm_dev->dev);
+err_devnum:
+	ib_ucm_free_dev(ucm_dev);
 err:
-	kfree(ucm_dev);
+	put_device(&ucm_dev->dev);
 	return;
 }
 
@@ -1323,7 +1322,9 @@ static void ib_ucm_remove_one(struct ib_device *device, void *client_data)
 	if (!ucm_dev)
 		return;
 
-	device_unregister(&ucm_dev->dev);
+	cdev_device_del(&ucm_dev->cdev, &ucm_dev->dev);
+	ib_ucm_free_dev(ucm_dev);
+	put_device(&ucm_dev->dev);
 }
 
 static CLASS_ATTR_STRING(abi_version, S_IRUGO,