On Thursday 17 September 2015 07:16:44 Pavel Machek wrote:

quoted

quoted

        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...

-- 
Pali Rohár
pali.rohar@gmail.com