Re: [PATCH][next] drm/gud: Use size_add() in call to struct_size()

[Gustavo A. R. Silva]

On 9/15/23 12:52, Kees Cook wrote:
> On Fri, Sep 15, 2023 at 12:43:20PM -0600, Gustavo A. R. Silva wrote:
> > If, for any reason, the open-coded arithmetic causes a wraparound, the
> > protection that `struct_size()` adds against potential integer overflows
> > is defeated. Fix this by hardening call to `struct_size()` with `size_add()`.
> >
> > Fixes: 40e1a70b4aed ("drm: Add GUD USB Display driver")
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/gud/gud_pipe.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/gud/gud_pipe.c b/drivers/gpu/drm/gud/gud_pipe.c
> > index d2f199ea3c11..a02f75be81f0 100644
> > --- a/drivers/gpu/drm/gud/gud_pipe.c
> > +++ b/drivers/gpu/drm/gud/gud_pipe.c
> > @@ -503,7 +503,7 @@ int gud_pipe_check(struct drm_simple_display_pipe *pipe,
> >   		return -ENOENT;
> >   
> >   	len = struct_size(req, properties,
> > -			  GUD_PROPERTIES_MAX_NUM + GUD_CONNECTOR_PROPERTIES_MAX_NUM);
> > +			  size_add(GUD_PROPERTIES_MAX_NUM, GUD_CONNECTOR_PROPERTIES_MAX_NUM));
>
> There are both constant expressions, so there's not too much value in
> wrapping them with size_add(), but for maintaining a common coding style
> for dealing with allocation sizes, I can be convinced of the change. :)

Yep; I've found a mix of constant expressions and variables doing open-coded arithmetic
in `struct_size()`, so I'm sending them all.

> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

Thanks!
--
Gustavo

> >   	req = kzalloc(len, GFP_KERNEL);
> >   	if (!req)
> >   		return -ENOMEM;
> > --
> > 2.34.1