Block all signals before sigreturn

sigactions are restored before memory and if a parent get a signal
which has a handler, it will get segmentation fault.

This problem will disappear, when we add a freezer, because
all processes will be resumed after restoring.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>

cr-restore.c

@@ -1207,6 +1207,16 @@ static int restore_task_with_children(int my_pid, char *pstree_path)
 	int *pids;
 	int fd, ret, i;
 	struct pstree_entry e;
+	sigset_t blockmask;
+
+	/* The block mask will be restored in sigresturn
+	 * This code should be removed, when a freezer will be added */
+	sigfillset(&blockmask);
+	ret = sigprocmask(SIG_BLOCK, &blockmask, NULL);
+	if (ret) {
+		pr_perror("%d: Can't block signals\n", my_pid);
+		exit(1);
+	}
 
 	pr_info("%d: Starting restore\n", my_pid);