Re: [Linux-fbdev-devel] fbcmap: non working tests on unsigned cmap->start

[Geert Uytterhoeven]

On Mon, Apr 27, 2009 at 13:58, Roel Kluin <roel.kluin@xxxxxxxxx> wrote:
> Ville SyrjÃlà wrote:
>> On Sun, Apr 26, 2009 at 02:20:47PM +0200, Roel Kluin wrote:
>>> cmap->start is unsigned,
>
>>>> On Thu, Apr 23, 2009 at 01:41:10PM -0700, Andrew Morton wrote:
>>>>> argh.
>>>>>
>>>>> - Perhaps userspace can kill the kernel by sending a "negative"
>>>>> Â `start'. ÂRemoving the test will make it even less likely that we'll
>>>>> Â 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.
>
>> You would rather need something like
>> 'if (start+len > 1 << max(red.len, green.len, blue.len, transp.len))'
>
> what do you mean with `red.len'? is that `info->var.red.length'?

That's correct.

>> 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.
>
> I am fairly new so please review carefully.
>
> Not yet signed off-by: Roel Kluin <roel.kluin@xxxxxxxxx>

Looks OK, thx!

> ---
> diff --git a/drivers/video/fbcmap.c b/drivers/video/fbcmap.c
> index f53b9f1..b34e74e 100644
> --- a/drivers/video/fbcmap.c
> +++ b/drivers/video/fbcmap.c
> @@ -249,6 +249,7 @@ int fb_set_user_cmap(struct fb_cmap_user *cmap, struct fb_info *info)
> Â{
> Â Â Â Âint rc, size = cmap->len * sizeof(u16);
> Â Â Â Âstruct fb_cmap umap;
> + Â Â Â __u32 rgba_max = 0;
>
> Â Â Â Âmemset(&umap, 0, sizeof(struct fb_cmap));
> Â Â Â Ârc = fb_alloc_cmap(&umap, cmap->len, cmap->transp != NULL);
> @@ -261,13 +262,27 @@ int fb_set_user_cmap(struct fb_cmap_user *cmap, struct fb_info *info)
> Â Â Â Â Â Â Â Ârc = -EFAULT;
> Â Â Â Â Â Â Â Âgoto out;
> Â Â Â Â}
> +
> + Â Â Â if (cmap->start + cmap->len < cmap->start) {
> + Â Â Â Â Â Â Â rc = -EINVAL;
> + Â Â Â Â Â Â Â goto out;
> + Â Â Â }
> +
> Â Â Â Âumap.start = cmap->start;
> Â Â Â Âif (!lock_fb_info(info)) {
> Â Â Â Â Â Â Â Ârc = -ENODEV;
> Â Â Â Â Â Â Â Âgoto out;
> Â Â Â Â}
> - Â Â Â if (cmap->start < 0 || (!info->fbops->fb_setcolreg &&
> - Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â !info->fbops->fb_setcmap)) {
> +
> + Â Â Â rgba_max = max(info->var.red.length, info->var.green.length);
> + Â Â Â rgba_max = max(rgba_max, info->var.blue.length);
> + Â Â Â rgba_max = max(rgba_max, info->var.transp.length);
> +
> + Â Â Â if (cmap->start + cmap->len > 1 << rgba_max ||
> + Â Â Â Â Â Â Â Â Â Â Â !(info->fbops->fb_setcolreg ||
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â info->fbops->fb_setcmap) ||
> + Â Â Â Â Â Â Â Â Â Â Â !(info->fix.visual == FB_VISUAL_PSEUDOCOLOR ||
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â info->fix.visual == FB_VISUAL_TRUECOLOR)) {
> Â Â Â Â Â Â Â Ârc = -EINVAL;
> Â Â Â Â Â Â Â Âgoto out1;
> Â Â Â Â}
>
> ------------------------------------------------------------------------------
> Crystal Reports &#45; New Free Runtime and 30 Day Trial
> Check out the new simplified licensign option that enables unlimited
> royalty&#45;free distribution of the report engine for externally facing
> server and web deployment.
> http://p.sf.net/sfu/businessobjects
> _______________________________________________
> Linux-fbdev-devel mailing list
> Linux-fbdev-devel@xxxxxxxxxxxxxxxxxxxxx
> https://lists.sourceforge.net/lists/listinfo/linux-fbdev-devel
>



-- 
Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/