amifb: test virtual screen range before subtraction on unsigned

dx and dy are u32's, so the test should occur before the subtraction

Signed-off-by: Roel Kluin <12o3l@tiscali.nl>
Cc: Antonino Daplas <adaplas@pol.net>
Cc: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/video/amifb.c b/drivers/video/amifb.c
index 45c154ade9ca..0c549aa1cf87 100644
--- a/drivers/video/amifb.c
+++ b/drivers/video/amifb.c
@@ -2048,13 +2048,16 @@ static void amifb_copyarea(struct fb_info *info,
         width = x2 - dx;
         height = y2 - dy;
 
+        if (area->sx + dx < area->dx || area->sy + dy < area->dy)
+                return;
+
         /* update sx,sy */
         sx = area->sx + (dx - area->dx);
         sy = area->sy + (dy - area->dy);
 
         /* the source must be completely inside the virtual screen */
-        if (sx < 0 || sy < 0 || (sx + width) > info->var.xres_virtual ||
-            (sy + height) > info->var.yres_virtual)
+        if (sx + width > info->var.xres_virtual ||
+                        sy + height > info->var.yres_virtual)
                 return;
 
         if (dy > sy || (dy == sy && dx > sx)) {