[AGPGART] sanitise agp mode input on setup ioctl.

drivers/char/agp/frontend.c

@@ -805,11 +805,19 @@ static int agpioc_setup_wrap(agp_file_private * priv, unsigned long arg)
 {
 	agp_setup mode;
 
-	if (copy_from_user(&mode, (void *) arg, sizeof(agp_setup))) {
+	if (copy_from_user(&mode, (void *) arg, sizeof(agp_setup)))
 		return -EFAULT;
+
+	switch (mode.agp_mode) {
+		case 1:
+		case 2:
+		case 4:
+		case 8:
+			agp_enable(mode.agp_mode);
+			return 0;
+		default:;
 	}
-	agp_enable(mode.agp_mode);
-	return 0;
+	return -EINVAL;
 }
 
 static int agpioc_reserve_wrap(agp_file_private * priv, unsigned long arg)