Re: [PATCH] staging: vchiq_arm: Using copy_from_user() to copy data from userspace address

[Al Viro]

On Sat, May 22, 2021 at 01:34:29PM +0800, Nguyen Dinh Phi wrote:
> This commit to fix the following sparse warning:
> incorrect type in assignment (different address spaces)
> expected void *[assigned] userdata
> got void [noderef] __user *userdata
> 
> Signed-off-by: Nguyen Dinh Phi <phind.uet@xxxxxxxxx>
> ---
>  .../staging/vc04_services/interface/vchiq_arm/vchiq_arm.c    | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
> index afbf01b7364c..2a4fc599f977 100644
> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
> @@ -960,7 +960,10 @@ static int vchiq_irq_queue_bulk_tx_rx(struct vchiq_instance *instance,
>  			current->pid);
>  		userdata = &waiter->bulk_waiter;
>  	} else {
> -		userdata = args->userdata;
> +		if (copy_from_user(userdata, args->userdata, sizeof(args->userdata))) {

	The contents of userdata (local variable of type void *) is uninitialized at that
point.  Just what do you think that call of copy_from_user() would do?