Messages in this thread | | | Date | Thu, 23 Apr 2009 14:56:52 -0700 | From | Andrew Morton <> | Subject | Re: [Linux-fbdev-devel] fbcmap: non working tests on unsigned cmap->start |
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On Fri, 24 Apr 2009 00:47:38 +0300 Ville Syrj__l__ <syrjala@sci.fi> wrote:
> On Thu, Apr 23, 2009 at 01:41:10PM -0700, Andrew Morton wrote: > > On Tue, 21 Apr 2009 16:26:33 +0200 > > Roel Kluin <roel.kluin@gmail.com> wrote: > > > > > 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?) > > > > > > Otherwise you may want to apply the cleanup patch below > > > > > > Roel > > > ------------------------------>8-------------8<--------------------------------- > > > Remove redundant tests on unsigned > > > > > > Signed-off-by: Roel Kluin <roel.kluin@gmail.com> > > > --- > > > diff --git a/drivers/video/fbcmap.c b/drivers/video/fbcmap.c > > > index f53b9f1..958bf4e 100644 > > > --- a/drivers/video/fbcmap.c > > > +++ b/drivers/video/fbcmap.c > > > @@ -266,8 +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 && > > > - !info->fbops->fb_setcmap)) { > > > + if (!info->fbops->fb_setcolreg && !info->fbops->fb_setcmap) { > > > rc = -EINVAL; > > > goto out1; > > > } > > > > 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.
OK.
I wonder if all drivers _do_ check. It probably doesn't matter much, as it's a privileged operation (I assume?)
> > - If this bug doesn't exist, and there _is_ userspace which is > > legitimately sending in "negative" values of `start' (unlikely?) then > > we will break userspace if we fix this comparison. > > The comparison will always be false since 'start' is unsigned so how > would anything break?
By "fix this comparison" I meant converting it to
if ((signed)cmap->start < 0)
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