Re: [PATCH 02/24] bpfilter: fix up a sparse annotation

To: Christoph Hellwig <hch@xxxxxx>
Subject: Re: [PATCH 02/24] bpfilter: fix up a sparse annotation
Cc: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>, Jakub Kicinski <kuba@xxxxxxxxxx>, Alexei Starovoitov <ast@xxxxxxxxxx>, Daniel Borkmann <daniel@xxxxxxxxxxxxx>, Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx>, Hideaki YOSHIFUJI <yoshfuji@xxxxxxxxxxxxxx>, Eric Dumazet <edumazet@xxxxxxxxxx>, linux-crypto@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx, bpf@xxxxxxxxxxxxxxx, netfilter-devel@xxxxxxxxxxxxxxx, coreteam@xxxxxxxxxxxxx, linux-sctp@xxxxxxxxxxxxxxx, linux-hams@xxxxxxxxxxxxxxx, linux-bluetooth@xxxxxxxxxxxxxxx, bridge@xxxxxxxxxxxxxxxxxxxxxxxxxx, linux-can@xxxxxxxxxxxxxxx, dccp@xxxxxxxxxxxxxxx, linux-decnet-user@xxxxxxxxxxxxxxxxxxxxx, linux-wpan@xxxxxxxxxxxxxxx, linux-s390@xxxxxxxxxxxxxxx, mptcp@xxxxxxxxxxxx, lvs-devel@xxxxxxxxxxxxxxx, rds-devel@xxxxxxxxxxxxxx, linux-afs@xxxxxxxxxxxxxxxxxxx, tipc-discussion@xxxxxxxxxxxxxxxxxxxxx, linux-x25@xxxxxxxxxxxxxxx
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date: Tue, 21 Jul 2020 06:28:21 +0100
On Tue, Jul 21, 2020 at 07:23:26AM +0200, Christoph Hellwig wrote:
> On Tue, Jul 21, 2020 at 04:40:16AM +0200, Luc Van Oostenryck wrote:
> > > = 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

Cast to unsigned long.  Or to uintptr_t if you want to be fancy.

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