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

[Phi Nguyen <phind.uet@gmail.com>]

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@gmail.com>
>> ---
>>   .../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.