[PATCH 7.1 2/8] driver core: faux: fix root device registration

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

7.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Johan Hovold <johan@kernel.org>

commit 580a795105dae2ef1622df72a27a8fb0605e2f6b upstream.

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
use-after-free 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@vger.kernel.org	# 7.0
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://patch.msgid.link/20260424153127.2647405-2-johan@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/base/faux.c |   22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

--- a/drivers/base/faux.c
+++ b/drivers/base/faux.c
@@ -133,6 +133,9 @@ struct faux_device *faux_device_create_w
 	struct device *dev;
 	int ret;
 
+	if (!faux_bus_root)
+		return NULL;
+
 	faux_obj = kzalloc_obj(*faux_obj);
 	if (!faux_obj)
 		return NULL;
@@ -232,19 +235,12 @@ EXPORT_SYMBOL_GPL(faux_device_destroy);
 
 int __init faux_bus_init(void)
 {
+	struct device *root;
 	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;
-	}
+	root = root_device_register("faux");
+	if (IS_ERR(root))
+		return PTR_ERR(root);
 
 	ret = bus_register(&faux_bus_type);
 	if (ret)
@@ -254,12 +250,14 @@ int __init faux_bus_init(void)
 	if (ret)
 		goto error_driver;
 
+	faux_bus_root = root;
+
 	return ret;
 
 error_driver:
 	bus_unregister(&faux_bus_type);
 
 error_bus:
-	device_unregister(faux_bus_root);
+	root_device_unregister(root);
 	return ret;
 }