Re: [PATCH] staging: comedi: cast to (unsigned int *)

Atul Gopinathan
2021-02-17T18:11:31Z

On Wed, Feb 17, 2021 at 06:35:15PM +0100, Greg KH wrote:
> On Wed, Feb 17, 2021 at 10:29:08PM +0530, Atul Gopinathan wrote:
> > Resolve the following warning generated by sparse:
> >
> > drivers/staging//comedi/comedi_fops.c:2956:23: warning: incorrect type in assignment (different address spaces)
> > drivers/staging//comedi/comedi_fops.c:2956:23: expected unsigned int *chanlist
> > drivers/staging//comedi/comedi_fops.c:2956:23: got void [noderef] <asn:1> *
> >
> > compat_ptr() has a return type of "void __user *"
> > as defined in "include/linux/compat.h"
> >
> > cmd->chanlist is of type "unsigned int *" as defined
> > in drivers/staging/comedi/comedi.h" in struct
> > comedi_cmd.
> >
> > Signed-off-by: Atul Gopinathan <atulgopinathan@gmail.com>
> > ---
> > drivers/staging/comedi/comedi_fops.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
> > index e85a99b68f31..fc4ec38012b4 100644
> > --- a/drivers/staging/comedi/comedi_fops.c
> > +++ b/drivers/staging/comedi/comedi_fops.c
> > @@ -2953,7 +2953,7 @@ static int get_compat_cmd(struct comedi_cmd *cmd,
> > cmd->scan_end_arg = v32.scan_end_arg;
> > cmd->stop_src = v32.stop_src;
> > cmd->stop_arg = v32.stop_arg;
> > - cmd->chanlist = compat_ptr(v32.chanlist);
> > + cmd->chanlist = (unsigned int __force *)compat_ptr(v32.chanlist);
>
> __force? That feels wrong, something is odd if that is ever needed.
>
> Are you _sure_ this is correct?

The same file has instances of "(usigned int __force *)" cast being
used on the same "cmd->chanlist". For reference:

At line 1797 of comedi_fops.c:
1796 /* restore chanlist pointer before copying back */
1797 cmd->chanlist = (unsigned int __force *)user_chanlist;
1798 cmd->data = NULL;

At line 1880:
1879 /* restore chanlist pointer before copying back */
1880 cmd->chanlist = (unsigned int __force *)user_chanlist;
1881 *copy = true;

Here "user_chanlist" is of type "unsigned int __user *".

Or perhaps, I shouldn't be relying on them?

Thanks!
Atul