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

[Phi Nguyen]

On 22/5/21 2:33 pm, Al Viro wrote:
> 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.
Sorry, That was my mistake.

> Just what do you think that call of copy_from_user() would do? 

Because according to the definition of struct vchiq_queue_bulk_transfer, 
the args->userdata pointer is userspace address.