[PATCH] driver core: faux: fix root device registration

[Johan Hovold]

A recent change made the faux bus root device be allocated dynamically
but failed to provide a release function to free the memory when the
last reference is dropped (on theoretical failure to register the device
or bus).

Fix this by using root_device_register() instead of open coding.

Also add the missing sanity check when registering faux devices to avoid
a NULL-pointer dereference if the bus failed to register (which would
previously have triggered a bunch of use-after-free warnings).

Fixes: 61b76d07d2b4 ("driver core: faux: stop using static struct device")
Cc: stable@xxxxxxxxxxxxxxx	# 7.0
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
---
 drivers/base/faux.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/drivers/base/faux.c b/drivers/base/faux.c
index fb3e42f21362..402ed119dfdf 100644
--- a/drivers/base/faux.c
+++ b/drivers/base/faux.c
@@ -133,6 +133,9 @@ struct faux_device *faux_device_create_with_groups(const char *name,
 	struct device *dev;
 	int ret;
 
+	if (IS_ERR_OR_NULL(faux_bus_root))
+		return NULL;
+
 	faux_obj = kzalloc_obj(*faux_obj);
 	if (!faux_obj)
 		return NULL;
@@ -234,17 +237,9 @@ int __init faux_bus_init(void)
 {
 	int ret;
 
-	faux_bus_root = kzalloc_obj(*faux_bus_root);
-	if (!faux_bus_root)
-		return -ENOMEM;
-
-	dev_set_name(faux_bus_root, "faux");
-
-	ret = device_register(faux_bus_root);
-	if (ret) {
-		put_device(faux_bus_root);
-		return ret;
-	}
+	faux_bus_root = root_device_register("faux");
+	if (IS_ERR(faux_bus_root))
+		return PTR_ERR(faux_bus_root);
 
 	ret = bus_register(&faux_bus_type);
 	if (ret)
@@ -260,6 +255,6 @@ int __init faux_bus_init(void)
 	bus_unregister(&faux_bus_type);
 
 error_bus:
-	device_unregister(faux_bus_root);
+	root_device_unregister(faux_bus_root);
 	return ret;
 }
-- 
2.53.0