[PATCH] media: meson: vdec: avoid double free on video register failure

[Guangshuo Li]

vdec_probe() allocates a video_device with video_device_alloc() and
releases it from the err_vdev_release 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)

  vdec_probe()
    -> err_vdev_release
       -> video_device_release(vdev)

Use video_device_release_empty() while registering the device so that
registration failure paths do not free vdev through vdev->release().
vdec_probe() then releases vdev exactly once from err_vdev_release.
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: 3e7f51bd9607 ("media: meson: add v4l2 m2m video decoder driver")
Signed-off-by: Guangshuo Li <lgs201920130244 at gmail.com>
---
 drivers/staging/media/meson/vdec/vdec.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/media/meson/vdec/vdec.c b/drivers/staging/media/meson/vdec/vdec.c
index 4b77ec1af5a7..2994e46cbc25 100644
--- a/drivers/staging/media/meson/vdec/vdec.c
+++ b/drivers/staging/media/meson/vdec/vdec.c
@@ -1074,7 +1074,7 @@ static int vdec_probe(struct platform_device *pdev)
 	mutex_init(&core->lock);
 
 	strscpy(vdev->name, "meson-video-decoder", sizeof(vdev->name));
-	vdev->release = video_device_release;
+	vdev->release = video_device_release_empty;
 	vdev->fops = &vdec_fops;
 	vdev->ioctl_ops = &vdec_ioctl_ops;
 	vdev->vfl_dir = VFL_DIR_M2M;
@@ -1089,6 +1089,7 @@ static int vdec_probe(struct platform_device *pdev)
 		dev_err(dev, "Failed registering video device\n");
 		goto err_vdev_release;
 	}
+	vdev->release = video_device_release;
 
 	return 0;
 
-- 
2.43.0