vga16fb: 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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/video/vga16fb.c b/drivers/video/vga16fb.c
index 9b3c5923365e..9d2751717896 100644
--- a/drivers/video/vga16fb.c
+++ b/drivers/video/vga16fb.c
@@ -1087,12 +1087,15 @@ static void vga16fb_copyarea(struct fb_info *info, const struct fb_copyarea *are
         width = x2 - dx;
         height = y2 - dy;
 
+        if (sx + dx < old_dx || sy + dy < old_dy)
+                return;
+
         /* update sx1,sy1 */
         sx += (dx - old_dx);
         sy += (dy - old_dy);
 
         /* the source must be completely inside the virtual screen */
-        if (sx < 0 || sy < 0 || (sx + width) > vxres || (sy + height) > vyres)
+        if (sx + width > vxres || sy + height > vyres)
                 return;
 
         switch (info->fix.type) {