/usr/include/bullet/LinearMath/ is in libbullet-dev 2.82-r2704+dfsg-2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/bullet/LinearMath/btAabbUtil2.h
/usr/include/bullet/LinearMath/btAlignedAllocator.h
/usr/include/bullet/LinearMath/btAlignedObjectArray.h
/usr/include/bullet/LinearMath/btConvexHull.h
/usr/include/bullet/LinearMath/btConvexHullComputer.h
/usr/include/bullet/LinearMath/btDefaultMotionState.h
/usr/include/bullet/LinearMath/btGeometryUtil.h
/usr/include/bullet/LinearMath/btGrahamScan2dConvexHull.h
/usr/include/bullet/LinearMath/btHashMap.h
/usr/include/bullet/LinearMath/btIDebugDraw.h
/usr/include/bullet/LinearMath/btList.h
/usr/include/bullet/LinearMath/btMatrix3x3.h
/usr/include/bullet/LinearMath/btMatrixX.h
/usr/include/bullet/LinearMath/btMinMax.h
/usr/include/bullet/LinearMath/btMotionState.h
/usr/include/bullet/LinearMath/btPolarDecomposition.h
/usr/include/bullet/LinearMath/btPoolAllocator.h
/usr/include/bullet/LinearMath/btQuadWord.h
/usr/include/bullet/LinearMath/btQuaternion.h
/usr/include/bullet/LinearMath/btQuickprof.h
/usr/include/bullet/LinearMath/btRandom.h
/usr/include/bullet/LinearMath/btScalar.h
/usr/include/bullet/LinearMath/btSerializer.h
/usr/include/bullet/LinearMath/btStackAlloc.h
/usr/include/bullet/LinearMath/btTransform.h
/usr/include/bullet/LinearMath/btTransformUtil.h
/usr/include/bullet/LinearMath/btVector3.h