Linux Ethernet Bridging - Jul 2020 - [Bridge] [PATCH 02/24] bpfilter: fix up a sparse annotation

On Mon, Jul 20, 2020 at 02:47:15PM +0200, Christoph Hellwig
wrote:
> The __user doesn't make sense when casting to an integer type.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
>  net/bpfilter/bpfilter_kern.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/bpfilter/bpfilter_kern.c b/net/bpfilter/bpfilter_kern.c
> index 977e9dad72ca4f..713b4b3d02005d 100644
> --- a/net/bpfilter/bpfilter_kern.c
> +++ b/net/bpfilter/bpfilter_kern.c
> @@ -49,7 +49,7 @@ static int __bpfilter_process_sockopt(struct sock *sk,
int optname,
>  	req.is_set = is_set;
>  	req.pid = current->pid;
>  	req.cmd = optname;
> -	req.addr = (long __force __user)optval;
> +	req.addr = (__force long)optval;
For casts to integers, even '__force' is not needed (since integers
can't be dereferenced, the concept of address-space is meaningless
for them, so it's never useful to warn when it's dropped and
'__force' is thus not needed).

-- Luc

On Tue, Jul 21, 2020 at 04:40:16AM +0200, Luc Van Oostenryck
wrote:
> >  	req.pid = current->pid;
> >  	req.cmd = optname;
> > -	req.addr = (long __force __user)optval;
> > +	req.addr = (__force long)optval;
> 
> For casts to integers, even '__force' is not needed (since integers
> can't be dereferenced, the concept of address-space is meaningless
> for them, so it's never useful to warn when it's dropped and
> '__force' is thus not needed).
That's what I thought. but if I remove it here I actually do get a
warning:

CHECK   net/bpfilter/bpfilter_kern.c
net/bpfilter/bpfilter_kern.c:52:21: warning: cast removes address space
'__user' of expression

Using this recent sparse build:

hch at brick:~/work/linux$ sparse --version
v0.6.2-49-g707c5017