Re: [PATCH] media: s5p-mfc: avoid double free on video register failure

[Marek Szyprowski <m.szyprowski@samsung.com>]

On 18.05.2026 15:09, Guangshuo Li wrote:
> s5p_mfc_probe() allocates video_device instances for both the decoder
> and encoder and releases them from the probe error paths if
> video_register_device() fails.
>
> This can double free a 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)
>
>   s5p_mfc_probe()
>     -> err_dec_reg or err_enc_reg
>        -> video_device_release(vdev)
>
> Use video_device_release_empty() while registering the decoder and encoder
> video devices so that registration failure paths do not free them through
> vdev->release(). s5p_mfc_probe() then releases each video_device exactly
> once from its error path. Restore video_device_release() after successful
> registration so the registered devices keep their normal lifetime
> handling.
>
> This issue was found by a static analysis tool I am developing.
>
> Fixes: d0ce898c39bf ("[media] s5p-mfc: Replaced commas with semicolons")
> Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
Frankly speaking I don't like this dancing with video_device_release_empty() and
video_device_release(). I would rather make video_device struct a part of device
state and use common release function.

> ---
>  drivers/media/platform/samsung/s5p-mfc/s5p_mfc.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/media/platform/samsung/s5p-mfc/s5p_mfc.c b/drivers/media/platform/samsung/s5p-mfc/s5p_mfc.c
> index 32eb402d439c..75abb0a8b7a9 100644
> --- a/drivers/media/platform/samsung/s5p-mfc/s5p_mfc.c
> +++ b/drivers/media/platform/samsung/s5p-mfc/s5p_mfc.c
> @@ -1376,7 +1376,7 @@ static int s5p_mfc_probe(struct platform_device *pdev)
>  	}
>  	vfd->fops	= &s5p_mfc_fops;
>  	vfd->ioctl_ops	= get_dec_v4l2_ioctl_ops();
> -	vfd->release	= video_device_release;
> +	vfd->release	= video_device_release_empty;
>  	vfd->lock	= &dev->mfc_mutex;
>  	vfd->v4l2_dev	= &dev->v4l2_dev;
>  	vfd->vfl_dir	= VFL_DIR_M2M;
> @@ -1395,7 +1395,7 @@ static int s5p_mfc_probe(struct platform_device *pdev)
>  	}
>  	vfd->fops	= &s5p_mfc_fops;
>  	vfd->ioctl_ops	= get_enc_v4l2_ioctl_ops();
> -	vfd->release	= video_device_release;
> +	vfd->release	= video_device_release_empty;
>  	vfd->lock	= &dev->mfc_mutex;
>  	vfd->v4l2_dev	= &dev->v4l2_dev;
>  	vfd->vfl_dir	= VFL_DIR_M2M;
> @@ -1416,6 +1416,8 @@ static int s5p_mfc_probe(struct platform_device *pdev)
>  		v4l2_err(&dev->v4l2_dev, "Failed to register video device\n");
>  		goto err_dec_reg;
>  	}
> +
> +	dev->vfd_dec->release = video_device_release;
>  	v4l2_info(&dev->v4l2_dev,
>  		  "decoder registered as /dev/video%d\n", dev->vfd_dec->num);
>  
> @@ -1424,6 +1426,8 @@ static int s5p_mfc_probe(struct platform_device *pdev)
>  		v4l2_err(&dev->v4l2_dev, "Failed to register video device\n");
>  		goto err_enc_reg;
>  	}
> +
> +	dev->vfd_enc->release = video_device_release;
>  	v4l2_info(&dev->v4l2_dev,
>  		  "encoder registered as /dev/video%d\n", dev->vfd_enc->num);
>  

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland