Re: [PATCH] media: hantro: fix use after free bug in hantro_release due to race condition

[Hans Verkuil]

On 07/03/2023 16:35, Zheng Wang wrote:
> In hantro_probe, vpu->watchdog_work is bound with
> hantro_watchdog. Then hantro_end_prepare_run may
> be called to start the work.
> 
> If we close the file or remove the module which will
> call hantro_release and hantro_remove to make cleanup,
> there may be a unfinished work. The possible sequence
> is as follows, which will cause a typical UAF bug.
> 
> The same thing will happen in hantro_release, and use
> ctx after freeing it.
> 
> Fix it by canceling the work before cleanup in hantro_release.
> 
> CPU0                  CPU1
> 
>                     |hantro_watchdog
> hantro_remove     |
>   v4l2_m2m_release  |
>     kfree(m2m_dev); |
>                     |
>                     | v4l2_m2m_get_curr_priv
>                     |   m2m_dev->curr_ctx //use
> 
> Signed-off-by: Zheng Wang <zyytlz.wz@xxxxxxx>
> ---
>  drivers/media/platform/verisilicon/hantro_drv.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/media/platform/verisilicon/hantro_drv.c b/drivers/media/platform/verisilicon/hantro_drv.c
> index b0aeedae7b65..cf00ccaa7829 100644
> --- a/drivers/media/platform/verisilicon/hantro_drv.c
> +++ b/drivers/media/platform/verisilicon/hantro_drv.c
> @@ -601,6 +601,7 @@ static int hantro_release(struct file *filp)
>  	 * No need for extra locking because this was the last reference
>  	 * to this file.
>  	 */
> +	cancel_delayed_work(&vpu->watchdog_work);
>  	v4l2_m2m_ctx_release(ctx->fh.m2m_ctx);
>  	v4l2_fh_del(&ctx->fh);
>  	v4l2_fh_exit(&ctx->fh);

drivers/media/platform/verisilicon/hantro_drv.c: In function ‘hantro_release’:
drivers/media/platform/verisilicon/hantro_drv.c:604:30: error: ‘vpu’ undeclared (first use in this function); did you mean ‘fpu’?
  604 |         cancel_delayed_work(&vpu->watchdog_work);
      |                              ^~~
      |                              fpu
drivers/media/platform/verisilicon/hantro_drv.c:604:30: note: each undeclared identifier is reported only once for each function it appears in

You clearly didn't compile this patch!

Regards,

	Hans