On Fri, 15 Mar 2024 09:44:08 +0100 Helge Deller wrote:
> On 3/5/24 14:51, Roman Smirnov wrote:
> > The expression htotal * vtotal can have a zero value on
> > overflow.
>
> I'm not sure if thos always results in zero in kernel on overflow.
> Might be architecture-depended too, but let's assume it
> can become zero, ....
>
> > It is necessary to prevent division by zero like in
> > fb_var_to_videomode().
> >
> > Found by Linux Verification Center (linuxtesting.org) with Svace.
> >
> > Signed-off-by: Roman Smirnov <r.smirnov@xxxxxx>
> > Reviewed-by: Sergey Shtylyov <s.shtylyov@xxxxxx>
> > ---
> > V1 -> V2: Replaced the code of the first version with a check.
> >
> > drivers/video/fbdev/core/fbmon.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/video/fbdev/core/fbmon.c b/drivers/video/fbdev/core/fbmon.c
> > index 79e5bfbdd34c..b137590386da 100644
> > --- a/drivers/video/fbdev/core/fbmon.c
> > +++ b/drivers/video/fbdev/core/fbmon.c
> > @@ -1344,7 +1344,7 @@ int fb_videomode_from_videomode(const struct videomode *vm,
> > vtotal = vm->vactive + vm->vfront_porch + vm->vback_porch +
> > vm->vsync_len;
> > /* prevent division by zero */
> > - if (htotal && vtotal) {
> > + if (htotal && vtotal && (vm->pixelclock / htotal >= vtotal)) {
>
> why don't you then simply check for
> if .. ((htotal * vtotal) == 0) ...
> instead?
>
> Helge
Thomas Zimmermann from the previous discussion said:
On Tue, 5 Mar 2024 11:18:05 +0100 Thomas Zimmerman wrote:
> Maybe use
>
> if (htotal && vtotal && (vm->pixelclock / htotal >= vtotal))
>
> for the test. That rules out overflowing multiplication and sets
> refresh to 0 in such cases.
This prevents overflow, which is also a problematic case.
