/usr/include/gtkdataboxmm-0.9/gtkdataboxmm/private/ is in libgtkdataboxmm-dev 0.9.4-3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/gtkdataboxmm-0.9/gtkdataboxmm/private/bars_p.h
/usr/include/gtkdataboxmm-0.9/gtkdataboxmm/private/cross_simple_p.h
/usr/include/gtkdataboxmm-0.9/gtkdataboxmm/private/databox_p.h
/usr/include/gtkdataboxmm-0.9/gtkdataboxmm/private/graph_p.h
/usr/include/gtkdataboxmm-0.9/gtkdataboxmm/private/grid_p.h
/usr/include/gtkdataboxmm-0.9/gtkdataboxmm/private/lines_p.h
/usr/include/gtkdataboxmm-0.9/gtkdataboxmm/private/markers_p.h
/usr/include/gtkdataboxmm-0.9/gtkdataboxmm/private/points_p.h
/usr/include/gtkdataboxmm-0.9/gtkdataboxmm/private/ruler_p.h
/usr/include/gtkdataboxmm-0.9/gtkdataboxmm/private/scale_p.h
/usr/include/gtkdataboxmm-0.9/gtkdataboxmm/private/xyc_graph_p.h