files: Prepare clone_service_fd() for overlaping ranges.

In normal life this is impossible. But in case of big
fdt::nr number (many processes, sharing the same files),
and custom service_fd_base, normal (!CLONE_FILES) child
of such process may have overlaping service fds with
parent's fdt. This patch introduces "memmove()" behavior
(currently there is "memcpy()" behavior) and this will
be used in next patch.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/util.c

@@ -568,8 +568,13 @@ int clone_service_fd(struct pstree_item *me)
 	if (service_fd_id == id)
 		return 0;
 
-	for (i = SERVICE_FD_MIN + 1; i < SERVICE_FD_MAX; i++)
-		move_service_fd(me, i, id, new_base);
+	/* Dup sfds in memmove() style: they may overlap */
+	if (get_service_fd(LOG_FD_OFF) > __get_service_fd(LOG_FD_OFF, id))
+		for (i = SERVICE_FD_MIN + 1; i < SERVICE_FD_MAX; i++)
+			move_service_fd(me, i, id, new_base);
+	else
+		for (i = SERVICE_FD_MAX - 1; i > SERVICE_FD_MIN; i--)
+			move_service_fd(me, i, id, new_base);
 
 	service_fd_id = id;
 	ret = 0;