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>

diff --git a/drivers/video/fbdev/sbuslib.c b/drivers/video/fbdev/sbuslib.c
index af6fc97f4ba4a5fac8cf2f100616f3cdf33a8aae..a436d44f1b7fbf4e2fe2447de21a6aa5a4903cde 100644 (file)
--- a/drivers/video/fbdev/sbuslib.c
+++ b/drivers/video/fbdev/sbuslib.c
@@ -122,7 +122,7 @@ int sbusfb_ioctl_helper(unsigned long cmd, unsigned long arg,
                unsigned char __user *ured;
                unsigned char __user *ugreen;
                unsigned char __user *ublue;
-               int index, count, i;
+               unsigned int index, count, i;
 
                if (get_user(index, &c->index) ||
                    __get_user(count, &c->count) ||
@@ -161,7 +161,7 @@ int sbusfb_ioctl_helper(unsigned long cmd, unsigned long arg,
                unsigned char __user *ugreen;
                unsigned char __user *ublue;
                struct fb_cmap *cmap = &info->cmap;
-               int index, count, i;
+               unsigned int index, count, i;
                u8 red, green, blue;
 
                if (get_user(index, &c->index) ||