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

[Guangshuo Li <lgs201920130244@gmail.com>]

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>
---
 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);
 
-- 
2.43.0