[PATCH 3.16 023/410] fbdev: Fixing arbitrary kernel leak in case FBIOGETCMAP_SPARC in sbusfb_ioctl_helper().

[Ben Hutchings]

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Malone <peter.malone@xxxxxxxxx>

commit 250c6c49e3b68756b14983c076183568636e2bde upstream.

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@xxxxxxxxx>
Acked-by: Mathieu Malaterre <malat@xxxxxxxxxx>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/video/fbdev/sbuslib.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/video/fbdev/sbuslib.c
+++ b/drivers/video/fbdev/sbuslib.c
@@ -121,7 +121,7 @@ int sbusfb_ioctl_helper(unsigned long cm
 		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) ||
@@ -160,7 +160,7 @@ int sbusfb_ioctl_helper(unsigned long cm
 		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) ||