sfds: Protect service fds

Mark area, where service fds modifications are prohibited.

v4: New
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/cr-restore.c

@@ -1181,6 +1181,7 @@ static int restore_one_task(int pid, CoreEntry *core)
 		ret = restore_one_zombie(core);
 	else if (current->pid->state == TASK_HELPER) {
 		ret = restore_one_helper();
+		sfds_protected = false;
 		close_image_dir();
 		close_proc();
 		for (i = SERVICE_FD_MIN + 1; i < SERVICE_FD_MAX; i++)
@@ -1709,6 +1710,8 @@ static int restore_task_with_children(void *_arg)
 	if (populate_pid_proc())
 		goto err;
 
+	sfds_protected = true;
+
 	if (unmap_guard_pages(current))
 		goto err;
 
@@ -3436,6 +3439,7 @@ static int sigreturn_restore(pid_t pid, struct task_restore_args *task_args, uns
 	if (restore_fs(current))
 		goto err;
 
+	sfds_protected = false;
 	close_image_dir();
 	close_proc();
 	close_service_fd(TRANSPORT_FD_OFF);

criu/files.c

@@ -1247,7 +1247,9 @@ int prepare_fds(struct pstree_item *me)
 	 * correct /tasks file if it is in a different cgroup
 	 * set than its parent
 	 */
+	sfds_protected = false;
 	close_service_fd(CGROUP_YARD);
+	sfds_protected = true;
 	set_proc_self_fd(-1); /* flush any proc cached fds we may have */
 
 	if (rsti(me)->fdt) {