/usr/lib/python2.7/dist-packages/notebook/static/components/backbone/backbone-min.js is in python-notebook 5.2.2-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/python2.7/dist-packages/notebook/static/components/backbone/../../../../../../../share/javascript/backbone/backbone.min.js