143 lines
5 KiB
JavaScript
143 lines
5 KiB
JavaScript
/** \file
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* \brief This file contains wrappers for the Gamepad API
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*
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* \see https://w3c.github.io/gamepad/
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*
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* \author Copyright (C) 2021 Libor Polcak
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*
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* \license SPDX-License-Identifier: GPL-3.0-or-later
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*/
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <https://www.gnu.org/licenses/>.
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//
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/** \file
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* \ingroup wrappers
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*
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* navigator.getGamepads() allows any page script to learn the gamepads
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* connected to the computer if the feature is not blocked by the
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* Feature-Policy.
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*
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* The "Fingerprinting the Fingerprinters" paper (see reference below) observed
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* that the interface is used in the wild to fingerprint users. As it is likely
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* that only a minority of users have a gamepad connected and the API
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* provides additional information on the HW, it is likely that users with
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* a gamepad connected are easily fingerprintable.
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*
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* As we expect that the majority of the users does not have a gamepad
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* connected, we provide only a single mitigation - the wrapped APIs return
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* an empty list.
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*
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* \bug The standard provides an event `gamepadconnected` and
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* `gamepaddisconnected` that fires at least on the window object. We do not
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* mitigate the event to fire and consequently, it is possible that an
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* adversary can learn that a gamepad was (dis)connected but there was no
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* change in the result of the `navigator.getGamepads()` API.
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*
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* The gamepad representing object carries a timestamp of the last change of
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* the gamepad. As we allow wrapping of several ways to obtain timestamps,
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* we need to provide the same precision for the Gamepad object.
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*
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* \see U. Iqbal, S. Englehardt and Z. Shafiq, [Fingerprinting the
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* Fingerprinters: Learning to Detect Browser Fingerprinting
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* Behaviors](https://github.com/uiowa-irl/FP-Inspector/blob/master/Data/potential_fingerprinting_APIs.md)
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* in 2021 2021 IEEE Symposium on Security and Privacy (SP), San Francisco,
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* CA, US, 2021 pp. 283-301
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*/
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(function() {
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var remember_past_ts_values = `var precision = args[0];
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var doNoise = args[1];
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var pastValues = {};
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${rounding_function}
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${noise_function}
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var mitigationF = rounding_function;
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if (doNoise === true){
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mitigationF = function(value, precision) {
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let params = [value, precision];
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if (params in pastValues) {
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return pastValues[params];
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}
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let result = noise_function(...params);
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pastValues[params] = result;
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return result;
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}
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}
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`;
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var wrappers = [
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{
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parent_object: "Navigator.prototype",
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parent_object_property: "getGamepads",
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wrapped_objects: [{
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original_name: "Navigator.prototype.getGamepads",
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wrapped_name: "origGamepads",
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}],
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helping_code: "",
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wrapping_function_body: `
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origGamepadsRes = origGamepads.call(navigator);
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if (Array.isArray(origGamepadsRes)) {
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// e.g. Gecko
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return new window.Array();
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}
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else {
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// e.g. Chromium based
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var l = new window.Object();
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// Based on our experiments and web search results like
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// https://stackoverflow.com/questions/41251051/is-the-html5-gamepad-api-limited-to-only-4-controllers
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// https://stackoverflow.com/questions/32619456/navigator-getgamepads-return-an-array-of-undefineds
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// we try to mimic common value of the property
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l[0] = null;
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l[1] = null;
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l[2] = null;
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l[3] = null;
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l.length = 4;
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window.Object.setPrototypeOf(l, origGamepadsRes.__proto__);
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return l;
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}
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`,
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},
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{
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/**
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* \see https://developer.mozilla.org/en-US/docs/Web/API/Gamepad/timestamp
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* \note that at the time of the writing of the prototype, the timestamp
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* property was not supported by any browser.
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*/
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parent_object: "Gamepad.prototype",
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parent_object_property: "timestamp",
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wrapped_objects: [],
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helping_code: remember_past_ts_values + `let origGet = Object.getOwnPropertyDescriptor(Gamepad.prototype, "timestamp").get`,
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post_wrapping_code: [
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{
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code_type: "object_properties",
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parent_object: "Gamepad.prototype",
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parent_object_property: "timestamp",
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wrapped_objects: [],
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/** \brief replaces Gamepad.timestamp getter to create
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* a timestamp with the desired precision.
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*/
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wrapped_properties: [
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{
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property_name: "get",
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property_value: `
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function() {
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return mitigationF(origGet.call(this), precision);
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}`,
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},
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],
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}
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],
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},
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]
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add_wrappers(wrappers);
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})()
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