Re: [PATCH v2 RESEND] media: hackrf: fix to not free memory after the device is registered in hackrf_probe()

[Hans Verkuil]

Hi Jeongjun Park,

On 04/09/2025 07:42, Jeongjun Park wrote:
> In hackrf driver, the following race condition occurs:
> ```
> 		CPU0						CPU1
> hackrf_probe()
>   kzalloc(); // alloc hackrf_dev
>   ....
>   v4l2_device_register();
>   ....
> 						open("/path/to/dev"); // open hackrf dev
> 						....
>   v4l2_device_unregister();
>   ....
>   kfree(); // free hackrf_dev
>   ....
> 						ioctl(fd, ...);
> 						  v4l2_ioctl();
> 						    video_is_registered() // UAF!!
> 						....
> 						close(fd);
> 						  v4l2_release() // UAF!!
> 						    hackrf_video_release()
> 						      kfree(); // DFB!!
> ```
> 
> When a V4L2 or video device is unregistered, the device node is removed so
> new open() calls are blocked.
> 
> However, file descriptors that are already open-and any in-flight I/O-do
> not terminate immediately; they remain valid until the last reference is
> dropped and the driver's release() is invoked.
> 
> Therefore, freeing device memory on the error path after hackrf_probe()
> has registered dev it will lead to a race to use-after-free vuln, since
> those already-open handles haven't been released yet.
> 
> And since release() free memory too, race to use-after-free and 
> double-free vuln occur.
> 
> To prevent this, if device is registered from probe(), it should be
> modified to free memory only through release() rather than calling
> kfree() directly.
> 
> Cc: <stable@xxxxxxxxxxxxxxx>
> Reported-by: syzbot+6ffd76b5405c006a46b7@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=6ffd76b5405c006a46b7
> Reported-by: syzbot+f1b20958f93d2d250727@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=f1b20958f93d2d250727
> Fixes: 8bc4a9ed8504 ("[media] hackrf: add support for transmitter")
> Signed-off-by: Jeongjun Park <aha310510@xxxxxxxxx>
> ---
> v2: Fix incorrect patch description style and CC stable mailing list
> - Link to v1: https://lore.kernel.org/all/20250822142729.1156816-1-aha310510@xxxxxxxxx/
> ---
>  drivers/media/usb/hackrf/hackrf.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/media/usb/hackrf/hackrf.c b/drivers/media/usb/hackrf/hackrf.c
> index 0b50de8775a3..d7a84422193d 100644
> --- a/drivers/media/usb/hackrf/hackrf.c
> +++ b/drivers/media/usb/hackrf/hackrf.c
> @@ -1515,6 +1515,8 @@ static int hackrf_probe(struct usb_interface *intf,
>  	video_unregister_device(&dev->rx_vdev);
>  err_v4l2_device_unregister:
>  	v4l2_device_unregister(&dev->v4l2_dev);

Instead of v4l2_device_unregister() this should call v4l2_device_put().
Otherwise the memory will never be freed since the v4l2_device refcount
will never reach 0.

> +	dev_dbg(&intf->dev, "failed=%d\n", ret);

Drop this line, it doesn't add anything.

Regards,

	Hans

> +	return ret;
>  err_v4l2_ctrl_handler_free_tx:
>  	v4l2_ctrl_handler_free(&dev->tx_ctrl_handler);
>  err_v4l2_ctrl_handler_free_rx:
> --
>