/usr/include/pcl-1.8/pcl/ml/ is in libpcl-dev 1.8.1+dfsg1-2ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/pcl-1.8/pcl/ml/branch_estimator.h
/usr/include/pcl-1.8/pcl/ml/decision_forest.h
/usr/include/pcl-1.8/pcl/ml/decision_forest_evaluator.h
/usr/include/pcl-1.8/pcl/ml/decision_forest_trainer.h
/usr/include/pcl-1.8/pcl/ml/decision_tree.h
/usr/include/pcl-1.8/pcl/ml/decision_tree_data_provider.h
/usr/include/pcl-1.8/pcl/ml/decision_tree_evaluator.h
/usr/include/pcl-1.8/pcl/ml/decision_tree_trainer.h
/usr/include/pcl-1.8/pcl/ml/densecrf.h
/usr/include/pcl-1.8/pcl/ml/feature_handler.h
/usr/include/pcl-1.8/pcl/ml/fern.h
/usr/include/pcl-1.8/pcl/ml/fern_evaluator.h
/usr/include/pcl-1.8/pcl/ml/fern_trainer.h
/usr/include/pcl-1.8/pcl/ml/kmeans.h
/usr/include/pcl-1.8/pcl/ml/multi_channel_2d_comparison_feature.h
/usr/include/pcl-1.8/pcl/ml/multi_channel_2d_comparison_feature_handler.h
/usr/include/pcl-1.8/pcl/ml/multi_channel_2d_data_set.h
/usr/include/pcl-1.8/pcl/ml/multiple_data_2d_example_index.h
/usr/include/pcl-1.8/pcl/ml/pairwise_potential.h
/usr/include/pcl-1.8/pcl/ml/permutohedral.h
/usr/include/pcl-1.8/pcl/ml/point_xy_32f.h
/usr/include/pcl-1.8/pcl/ml/point_xy_32i.h
/usr/include/pcl-1.8/pcl/ml/regression_variance_stats_estimator.h
/usr/include/pcl-1.8/pcl/ml/stats_estimator.h
/usr/include/pcl-1.8/pcl/ml/svm.h
/usr/include/pcl-1.8/pcl/ml/svm_wrapper.h