Messages in this thread | | | Date | Sun, 26 Apr 2009 16:15:05 +0300 | From | Ville Syrjälä <> | Subject | Re: [Linux-fbdev-devel] fbcmap: non working tests on unsigned cmap->start |
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On Sun, Apr 26, 2009 at 02:20:47PM +0200, Roel Kluin wrote: > cmap->start is unsigned, A negative start could result in incorrect > colors. `start' is used as the starting index for the hardware palette, > 'start+len-1' is the last index. > > Signed-off-by: Roel Kluin <roel.kluin@gmail.com> > --- > >>> vi include/linux/fb.h +478 > >>> > >>> Note that struct fb_cmap_user cmap->start in fb_set_user_cmap() is unsigned. > >>> Should there maybe be a test: > >>> > >>> if (cmap->start > MAX || ...) > >>> > >>> (and what should MAX be then?) > >>> > > > On Thu, Apr 23, 2009 at 01:41:10PM -0700, Andrew Morton wrote: > >> argh. > >> > >> - Perhaps userspace can kill the kernel by sending a "negative" > >> `start'. Removing the test will make it even less likely that we'll > >> fix this bug. > > > > Shouldn't happen. 'start' is used as the starting index for the hardware > > palette, 'start+len-1' is the last index. All drivers should already check > > the passed values since the maximum index depends on the display mode. > > And I suppose the worst thing that could happen if the driver fails to > > check the values would be incorrect colors. > > Thanks for your explanation, I think this should fix it? > > diff --git a/drivers/video/fbcmap.c b/drivers/video/fbcmap.c > index f53b9f1..ea62d87 100644 > --- a/drivers/video/fbcmap.c > +++ b/drivers/video/fbcmap.c > @@ -266,7 +266,7 @@ int fb_set_user_cmap(struct fb_cmap_user *cmap, struct fb_info *info) > rc = -ENODEV; > goto out; > } > - if (cmap->start < 0 || (!info->fbops->fb_setcolreg && > + if (cmap->start >= cmap->len || (!info->fbops->fb_setcolreg && > !info->fbops->fb_setcmap)) { > rc = -EINVAL; > goto out1;
That's not correct. There's nothing wrong with having 'start' >= 'len'.
You would rather need something like 'if (start+len > 1 << max(red.len, green.len, blue.len, transp.len))' and a check to make sure that start+len doesn't overflow.
Oh and I guess it should also check that the visual is pseudocolor or directcolor.
-- Ville Syrjälä syrjala@sci.fi http://www.sci.fi/~syrjala/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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