fbdev: Fixing arbitrary kernel leak in case FBIOGETCMAP_SPARC in sbusfb_ioctl_helper().

Fixing arbitrary kernel leak in case FBIOGETCMAP_SPARC in
sbusfb_ioctl_helper().

'index' is defined as an int in sbusfb_ioctl_helper().
We retrieve this from the user:
if (get_user(index, &c->index) ||
    __get_user(count, &c->count) ||
    __get_user(ured, &c->red) ||
    __get_user(ugreen, &c->green) ||
    __get_user(ublue, &c->blue))
       return -EFAULT;

and then we use 'index' in the following way:
red = cmap->red[index + i] >> 8;
green = cmap->green[index + i] >> 8;
blue = cmap->blue[index + i] >> 8;

This is a classic information leak vulnerability. 'index' should be
an unsigned int, given its usage above.

This patch is straight-forward; it changes 'index' to unsigned int
in two switch-cases: FBIOGETCMAP_SPARC && FBIOPUTCMAP_SPARC.

This patch fixes CVE-2018-6412.

Signed-off-by: Peter Malone <peter.malone@gmail.com>
Acked-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
int sbusfb_compat_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
{
	switch (cmd) {
	case FBIOGTYPE:
	case FBIOSATTR:
	case FBIOGATTR:
	case FBIOSVIDEO:
	case FBIOGVIDEO:
	case FBIOGCURSOR32:	/* This is not implemented yet.
				   Later it should be converted... */
	case FBIOSCURPOS:
	case FBIOGCURPOS:
	case FBIOGCURMAX:
		return info->fbops->fb_ioctl(info, cmd, arg);
	case FBIOPUTCMAP32:
		return fbiogetputcmap(info, cmd, arg);
	case FBIOGETCMAP32:
		return fbiogetputcmap(info, cmd, arg);
	case FBIOSCURSOR32:
		return fbiogscursor(info, arg);
	default:
		return -ENOIOCTLCMD;
	}
}

int sbusfb_compat_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
{
	switch (cmd) {
	case FBIOGTYPE:
	case FBIOSATTR:
	case FBIOGATTR:
	case FBIOSVIDEO:
	case FBIOGVIDEO:
	case FBIOGCURSOR32:	/* This is not implemented yet.
				   Later it should be converted... */
	case FBIOSCURPOS:
	case FBIOGCURPOS:
	case FBIOGCURMAX:
		return info->fbops->fb_ioctl(info, cmd, arg);
	case FBIOPUTCMAP32:
		return fbiogetputcmap(info, cmd, arg);
	case FBIOGETCMAP32:
		return fbiogetputcmap(info, cmd, arg);
	case FBIOSCURSOR32:
		return fbiogscursor(info, arg);
	default:
		return -ENOIOCTLCMD;
	}
}
