Re: omapdss: Division by zero in kernel

Pali Rohár
2015-09-25T11:34:34Z

On Thursday 17 September 2015 07:16:44 Pavel Machek wrote:
>
> > > if (image->depth == 1) {
> > > if (p->fix.visual == FB_VISUAL_TRUECOLOR ||
> > > p->fix.visual == FB_VISUAL_DIRECTCOLOR) {
> > > fgcolor = ((u32*)(p->pseudo_palette))[image->fg_color];
> > > bgcolor = ((u32*)(p->pseudo_palette))[image->bg_color];
> > > } else {
> > > fgcolor = image->fg_color;
> > > bgcolor = image->bg_color;
> > > }
> > >
> > > if (32 % bpp == 0 && !start_index && !pitch_index &&
> > > ((width & (32/bpp-1)) == 0) &&
> > > bpp >= 8 && bpp <= 32)
> > > fast_imageblit(image, p, dst1, fgcolor, bgcolor);
> > > else
> > > slow_imageblit(image, p, dst1, fgcolor, bgcolor,
> > > start_index, pitch_index);
> > > } else
> > > color_imageblit(image, p, dst1, start_index, pitch_i
> > >
> > >
> > > Notice that bpp is not checked for zero, and thus bpp==0 is totally
> > > feasible? resulting in 32/bpp crashing the kernel?
> > >
> >
> > Hm... this could really be a problem! But how to patch it? Which branch
> > should be called (fast_ or slow_ function) if bpp is zero?
> >
> > And is there some way to force kernel to dump backtrace into dmesg when
> > division by zero occur?
>
> You can do WARN_ON(bpp==1) ... and should probably return in that
> case.
>
> Pavel

Does not make sense to call slow_ function? In that if condition check
also that bpp is nonzero...