timesync: check cmsg length

src/timesync/timesyncd-manager.c

@@ -471,6 +471,8 @@ static int manager_receive_response(sd_event_source *source, int fd, uint32_t re
 
                 switch (cmsg->cmsg_type) {
                 case SCM_TIMESTAMPNS:
+                        assert(cmsg->cmsg_len == CMSG_LEN(sizeof(struct timespec)));
+
                         recv_time = (struct timespec *) CMSG_DATA(cmsg);
                         break;
                 }