[PATCH] media: mx2-emmaprp: avoid double free on video register failure

[Guangshuo Li]

emmaprp_probe() allocates a video_device with video_device_alloc() and
releases it from the rel_vdev error path if video_register_device()
fails.

This can double free the video_device when __video_register_device()
reaches device_register() and that call fails:

  video_register_device()
    -> __video_register_device()
       -> device_register() fails
          -> put_device(&vdev->dev)
             -> v4l2_device_release()
                -> vdev->release(vdev)
                   -> video_device_release(vdev)

  emmaprp_probe()
    -> rel_vdev
       -> video_device_release(vfd)

Use video_device_release_empty() while registering the device so that
registration failure paths do not free vfd through vdev->release().
emmaprp_probe() then releases vfd exactly once from rel_vdev. Restore
video_device_release() after successful registration so the registered
device keeps its normal lifetime handling.

This issue was found by a static analysis tool I am developing.

Fixes: 8091cb7d9ce6 ("[media] MEM2MEM: Add support for eMMa-PrP mem2mem operations")
Signed-off-by: Guangshuo Li <lgs201920130244@xxxxxxxxx>
---
 drivers/media/platform/nxp/mx2_emmaprp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/media/platform/nxp/mx2_emmaprp.c b/drivers/media/platform/nxp/mx2_emmaprp.c
index d51a62100778..a27809b7730e 100644
--- a/drivers/media/platform/nxp/mx2_emmaprp.c
+++ b/drivers/media/platform/nxp/mx2_emmaprp.c
@@ -834,6 +834,7 @@ static int emmaprp_probe(struct platform_device *pdev)
 	}
 
 	*vfd = emmaprp_videodev;
+	vfd->release = video_device_release_empty;
 	vfd->lock = &pcdev->dev_mutex;
 	vfd->v4l2_dev = &pcdev->v4l2_dev;
 
@@ -867,6 +868,7 @@ static int emmaprp_probe(struct platform_device *pdev)
 		v4l2_err(&pcdev->v4l2_dev, "Failed to register video device\n");
 		goto rel_m2m;
 	}
+	vfd->release = video_device_release;
 
 	return 0;
 
-- 
2.43.0