linux-kernel - Re: omapdss: Division by zero in kernel

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Date:	Thu, 17 Sep 2015 07:16:44 +0200
From:	Pavel Machek <pavel@....cz>
To:	Pali Rohár <pali.rohar@...il.com>
Cc:	Peter Teoh <htmldeveloper@...il.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Jyri Sarha <jsarha@...com>, omap <linux-omap@...r.kernel.org>,
	linux-fbdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Sebastian Reichel <sre@...nel.org>,
	Aaro Koskinen <aaro.koskinen@....fi>,
	Tony Lindgren <tony@...mide.com>, Nishanth Menon <nm@...com>
Subject: Re: omapdss: Division by zero in kernel


> >         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
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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