/usr/include/CGAL/Convex_decomposition_3/ is in libcgal-dev 4.2-5ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/CGAL/Convex_decomposition_3/Edge_sorter.h
/usr/include/CGAL/Convex_decomposition_3/External_structure_builder.h
/usr/include/CGAL/Convex_decomposition_3/Insert_vertex_into_edge.h
/usr/include/CGAL/Convex_decomposition_3/Ray_hit_generator.h
/usr/include/CGAL/Convex_decomposition_3/Ray_hit_generator2.h
/usr/include/CGAL/Convex_decomposition_3/Reflex_edge_searcher.h
/usr/include/CGAL/Convex_decomposition_3/Reflex_vertex_searcher.h
/usr/include/CGAL/Convex_decomposition_3/SFace_separator.h
/usr/include/CGAL/Convex_decomposition_3/SM_walls.h
/usr/include/CGAL/Convex_decomposition_3/Single_wall_creator.h
/usr/include/CGAL/Convex_decomposition_3/Single_wall_creator2.h
/usr/include/CGAL/Convex_decomposition_3/Single_wall_creator3.h
/usr/include/CGAL/Convex_decomposition_3/YVertical_wall_builder.h
/usr/include/CGAL/Convex_decomposition_3/is_reflex_sedge.h