[PATCH v3] media: v4l2-dev: fix error handling in __video_register_device()

[PATCH v3] media: v4l2-dev: fix error handling in __video_register_device()

[Ma Ke]

Once device_register() failed, we should call put_device() to
decrement reference count for cleanup. Or it could cause memory leak.
And move callback function v4l2_device_release() and v4l2_device_get()
before put_device().

As comment of device_register() says, 'NOTE: _Never_ directly free
@dev after calling this function, even if it returned an error! Always
use put_device() to give up the reference initialized in this function
instead.'

Found by code review.

Cc: stable@vger.kernel.org
Fixes: dc93a70cc7f9 ("V4L/DVB (9973): v4l2-dev: use the release callback from device instead of cdev")
Signed-off-by: Ma Ke <make24@iscas.ac.cn>
---
Changes in v3:
- modified the patch to balance the v4l2_device reference count;
- changed the Fix tag as suggestions;
Changes in v2:
- modified the patch as no callback function before put_device().
---
 drivers/media/v4l2-core/v4l2-dev.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
index 5bcaeeba4d09..4c7e1008a152 100644
--- a/drivers/media/v4l2-core/v4l2-dev.c
+++ b/drivers/media/v4l2-core/v4l2-dev.c
@@ -1054,25 +1054,25 @@ int __video_register_device(struct video_device *vdev,
 	vdev->dev.class = &video_class;
 	vdev->dev.devt = MKDEV(VIDEO_MAJOR, vdev->minor);
 	vdev->dev.parent = vdev->dev_parent;
+	vdev->dev.release = v4l2_device_release;
 	dev_set_name(&vdev->dev, "%s%d", name_base, vdev->num);
+
+	/* Increase v4l2_device refcount*/
+	v4l2_device_get(vdev->v4l2_dev);
+
 	mutex_lock(&videodev_lock);
 	ret = device_register(&vdev->dev);
 	if (ret < 0) {
 		mutex_unlock(&videodev_lock);
 		pr_err("%s: device_register failed\n", __func__);
-		goto cleanup;
+		put_device(&vdev->dev);
+		return ret;
 	}
-	/* Register the release callback that will be called when the last
-	   reference to the device goes away. */
-	vdev->dev.release = v4l2_device_release;
-
+
 	if (nr != -1 && nr != vdev->num && warn_if_nr_in_use)
 		pr_warn("%s: requested %s%d, got %s\n", __func__,
 			name_base, nr, video_device_node_name(vdev));
 
-	/* Increase v4l2_device refcount */
-	v4l2_device_get(vdev->v4l2_dev);
-
 	/* Part 5: Register the entity. */
 	ret = video_register_media_controller(vdev);
 
-- 
2.25.1

Re: [PATCH v3] media: v4l2-dev: fix error handling in __video_register_device()

[Sakari Ailus]

On Wed, Mar 19, 2025 at 04:02:48PM +0800, Ma Ke wrote:
> Once device_register() failed, we should call put_device() to
> decrement reference count for cleanup. Or it could cause memory leak.
> And move callback function v4l2_device_release() and v4l2_device_get()
> before put_device().
> 
> As comment of device_register() says, 'NOTE: _Never_ directly free
> @dev after calling this function, even if it returned an error! Always
> use put_device() to give up the reference initialized in this function
> instead.'
> 
> Found by code review.
> 
> Cc: stable@vger.kernel.org
> Fixes: dc93a70cc7f9 ("V4L/DVB (9973): v4l2-dev: use the release callback from device instead of cdev")
> Signed-off-by: Ma Ke <make24@iscas.ac.cn>

Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>

-- 
Sakari Ailus