[PATCH v2] chardev: fix error handling in cdev_device_add()

[Yang Yingliang]

While doing fault injection test, I got the following report:

------------[ cut here ]------------
kobject: '(null)' (0000000039956980): is not initialized, yet kobject_put() is being called.
WARNING: CPU: 3 PID: 6306 at kobject_put+0x23d/0x4e0
CPU: 3 PID: 6306 Comm: 283 Tainted: G        W          6.1.0-rc2-00005-g307c1086d7c9 #1253
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:kobject_put+0x23d/0x4e0
Call Trace:
 <TASK>
 cdev_device_add+0x15e/0x1b0
 __iio_device_register+0x13b4/0x1af0 [industrialio]
 __devm_iio_device_register+0x22/0x90 [industrialio]
 max517_probe+0x3d8/0x6b4 [max517]
 i2c_device_probe+0xa81/0xc00

When device_add() is injected fault and returns error, if dev->devt is not set,
cdev_add() is not called, cdev_del() is not needed. Fix this by checking dev->devt
in error path.

Fixes: 233ed09d7fda ("chardev: add helper function to register char devs with a struct device")
Signed-off-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
---
v1 -> v2:
  Add information to update commit message.
  v1 link: https://lore.kernel.org/lkml/1959fa74-b06c-b8bc-d14f-b71e5c4290ee@xxxxxxxxxx/T/
---
 fs/char_dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/char_dev.c b/fs/char_dev.c
index ba0ded7842a7..3f667292608c 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -547,7 +547,7 @@ int cdev_device_add(struct cdev *cdev, struct device *dev)
 	}
 
 	rc = device_add(dev);
-	if (rc)
+	if (rc && dev->devt)
 		cdev_del(cdev);
 
 	return rc;
-- 
2.25.1