[PATCH] media: stm32: dma2d: avoid double free on video register failure

[Guangshuo Li <lgs201920130244@gmail.com>]

dma2d_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)

  dma2d_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().
dma2d_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: 002e8f0d5927 ("media: stm32-dma2d: STM32 DMA2D driver")
Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
---
 drivers/media/platform/st/stm32/dma2d/dma2d.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/media/platform/st/stm32/dma2d/dma2d.c b/drivers/media/platform/st/stm32/dma2d/dma2d.c
index a3ad19256859..0e36ddfa8c7b 100644
--- a/drivers/media/platform/st/stm32/dma2d/dma2d.c
+++ b/drivers/media/platform/st/stm32/dma2d/dma2d.c
@@ -651,6 +651,7 @@ static int dma2d_probe(struct platform_device *pdev)
 	}
 
 	*vfd = dma2d_videodev;
+	vfd->release = video_device_release_empty;
 	vfd->lock = &dev->mutex;
 	vfd->v4l2_dev = &dev->v4l2_dev;
 	vfd->device_caps = V4L2_CAP_VIDEO_M2M | V4L2_CAP_STREAMING;
@@ -669,6 +670,8 @@ static int dma2d_probe(struct platform_device *pdev)
 		goto free_m2m;
 	}
 
+	vfd->release = video_device_release;
+
 	video_set_drvdata(vfd, dev);
 	dev->vfd = vfd;
 	v4l2_info(&dev->v4l2_dev, "device registered as /dev/video%d\n",
-- 
2.43.0