Re: [PATCH v3] media: hackrf: fix to not free memory after the device is registered in hackrf_probe()

[Jeongjun Park]

Jeongjun Park <aha310510@xxxxxxxxx> wrote:
>
> In hackrf driver, the following race condition occurs:
> ```
>                 CPU0                                            CPU1
> hackrf_probe()
>   kzalloc(); // alloc hackrf_dev
>   ....
>   v4l2_device_register();
>   ....
>                                                 fd = sys_open("/path/to/dev"); // open hackrf fd
>                                                 ....
>   v4l2_device_unregister();
>   ....
>   kfree(); // free hackrf_dev
>   ....
>                                                 sys_ioctl(fd, ...);
>                                                   v4l2_ioctl();
>                                                     video_is_registered() // UAF!!
>                                                 ....
>                                                 sys_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>
> ---

Cc: Hans Verkuil <hverkuil+cisco@xxxxxxxxxx>