Haketilo

/**

 * This file is part of Haketilo.

 *

 * Function: Main content script that runs in all frames.

 *

 * Copyright (C) 2021 Wojtek Kosior

 * Copyright (C) 2021 jahoti

 *

 * This program is free software: you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation, either version 3 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * As additional permission under GNU GPL version 3 section 7, you

 * may distribute forms of that code without the copy of the GNU

 * GPL normally required by section 4, provided you include this

 * license notice and, in case of non-source distribution, a URL

 * through which recipients can access the Corresponding Source.

 * If you modify file(s) with this exception, you may extend this

 * exception to your version of the file(s), but you are not

 * obligated to do so. If you do not wish to do so, delete this

 * exception statement from your version.

 *

 * As a special exception to the GPL, any HTML file which merely

 * makes function calls to this code, and for that purpose

 * includes it by reference shall be deemed a separate work for

 * copyright law purposes. If you modify this code, you may extend

 * this exception to your version of the code, but you are not

 * obligated to do so. If you do not wish to do so, delete this

 * exception statement from your version.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program.  If not, see <https://www.gnu.org/licenses/>.

 *

 * I, Wojtek Kosior, thereby promise not to sue for violation of this file's

 * license. Although I request that you do not make use this code in a

 * proprietary program, I am not going to enforce this in court.

 */

/*

 * IMPORTS_START

 * IMPORT handle_page_actions

 * IMPORT extract_signed

 * IMPORT sign_data

 * IMPORT gen_nonce

 * IMPORT is_privileged_url

 * IMPORT is_chrome

 * IMPORT is_mozilla

 * IMPORT start_activity_info_server

 * IMPORT make_csp_rule

 * IMPORT csp_header_regex

 * IMPORTS_END

 */

document.content_loaded = document.readyState === "complete";

const wait_loaded = e => e.content_loaded ? Promise.resolve() :

      new Promise(c => e.addEventListener("DOMContentLoaded", c, {once: true}));

wait_loaded(document).then(() => document.content_loaded = true);

function extract_cookie_policy(cookie, min_time)

{

    let best_result = {time: -1};

    let policy = null;

    const extracted_signatures = [];

    for (const match of cookie.matchAll(/haketilo-(\w*)=([^;]*)/g)) {

	const new_result = extract_signed(...match.slice(1, 3));

	if (new_result.fail)

	    continue;

	extracted_signatures.push(match[1]);

	if (new_result.time < Math.max(min_time, best_result.time))

	    continue;

	/* This should succeed - it's our self-produced valid JSON. */

	const new_policy = JSON.parse(decodeURIComponent(new_result.data));

	if (new_policy.url !== document.URL)

	    continue;

	best_result = new_result;

	policy = new_policy;

    }

    return [policy, extracted_signatures];

}

function extract_url_policy(url, min_time)

{

    const [base_url, payload, anchor] =

	  /^([^#]*)#?([^#]*)(#?.*)$/.exec(url).splice(1, 4);

    const match = /^haketilo_([^_]+)_(.*)$/.exec(payload);

    if (!match)

	return [null, url];

    const result = extract_signed(...match.slice(1, 3));

    if (result.fail)

	return [null, url];

    const original_url = base_url + anchor;

    const policy = result.time < min_time ? null :

	  JSON.parse(decodeURIComponent(result.data));

    return [policy.url === original_url ? policy : null, original_url];

}

function employ_nonhttp_policy(policy)

{

    if (!policy.allow)

	return;

    policy.nonce = gen_nonce();

    const [base_url, target] = /^([^#]*)(#?.*)$/.exec(policy.url).slice(1, 3);

    const encoded_policy = encodeURIComponent(JSON.stringify(policy));

    const payload = "haketilo_" +

	  sign_data(encoded_policy, new Date().getTime()).join("_");

    const resulting_url = `${base_url}#${payload}${target}`;

    location.href = resulting_url;

    location.reload();

}

/*

 * In the case of HTML documents:

 * 1. When injecting some payload we need to sanitize <meta> CSP tags before

 *    they reach the document.

 * 2. Only <meta> tags inside <head> are considered valid by the browser and

 *    need to be considered.

 * 3. We want to detach <html> from document, wait until its <head> completes

 *    loading, sanitize it and re-attach <html>.

 * 4. We shall wait for anything to appear in or after <body> and take that as

 *    a sign <head> has finished loading.

 * 5. Otherwise, getting the `DOMContentLoaded' event on the document shall also

 *    be a sign that <head> is fully loaded.

 */

function make_body_start_observer(DOM_element, waiting)

{

    const observer = new MutationObserver(() => try_body_started(waiting));

    observer.observe(DOM_element, {childList: true});

    return observer;

}

function try_body_started(waiting)

{

    const body = waiting.detached_html.querySelector("body");

    if ((body && (body.firstChild || body.nextSibling)) ||

	waiting.doc.documentElement.nextSibling) {

	finish_waiting(waiting);

	return true;

    }

    if (body && waiting.observers.length < 2)

	waiting.observers.push(make_body_start_observer(body, waiting));

}

function finish_waiting(waiting)

{

    if (waiting.finished)

	return;

    waiting.finished = true;

    waiting.observers.forEach(observer => observer.disconnect());

    setTimeout(waiting.callback, 0);

}

function _wait_for_head(doc, detached_html, callback)

{

    const waiting = {doc, detached_html, callback, observers: []};

    if (try_body_started(waiting))

	return;

    waiting.observers = [make_body_start_observer(detached_html, waiting)];

    wait_loaded(doc).then(() => finish_waiting(waiting));

}

function wait_for_head(doc, detached_html)

{

    return new Promise(cb => _wait_for_head(doc, detached_html, cb));

}

const blocked_str = "blocked";

function block_attribute(node, attr, ns=null)

{

    const [hasa, geta, seta, rema] = ["has", "get", "set", "remove"]

	  .map(m => (n, ...args) => typeof ns === "string" ?

	       n[`${m}AttributeNS`](ns, ...args) : n[`${m}Attribute`](...args));

    /*

     * Disabling attributes by prepending `-blocked' allows them to still be

     * relatively easily accessed in case they contain some useful data.

     */

    const construct_name = [attr];

    while (hasa(node, construct_name.join("")))

	construct_name.unshift(blocked_str);

    while (construct_name.length > 1) {

	construct_name.shift();

	const name = construct_name.join("");

	seta(node, `${blocked_str}-${name}`, geta(node, name));

    }

    rema(node, attr);

}

/*

 * Used to disable `<script>'s and `<meta>'s that have not yet been added to

 * live DOM (doesn't work for those already added).

 */

function sanitize_meta(meta)

{

    if (csp_header_regex.test(meta.httpEquiv) && meta.content)

	block_attribute(meta, "content");

}

function sanitize_script(script)

{

    script.haketilo_blocked_type = script.getAttribute("type");

    script.type = "text/plain";

}

/*

 * Executed after `<script>' has been connected to the DOM, when it is no longer

 * eligible for being executed by the browser.

 */

function desanitize_script(script)

{

    script.setAttribute("type", script.haketilo_blocked_type);

    if ([null, undefined].includes(script.haketilo_blocked_type))

	script.removeAttribute("type");

    delete script.haketilo_blocked_type;

}

const bad_url_reg = /^data:([^,;]*ml|unknown-content-type)/i;

function sanitize_urls(element)

{

    for (const attr of [...element.attributes || []]

	       .filter(attr => /^(href|src|data)$/i.test(attr.localName))

	       .filter(attr => bad_url_reg.test(attr.value)))

	block_attribute(element, attr.localName, attr.namespaceURI);

}

function start_data_urls_sanitizing(doc)

{

    doc.querySelectorAll("*[href], *[src], *[data]").forEach(sanitize_urls);

    if (!doc.content_loaded) {

	const mutation_handler = m => m.addedNodes.forEach(sanitize_urls);

	const mo = new MutationObserver(ms => ms.forEach(mutation_handler));

	mo.observe(doc, {childList: true, subtree: true});

	wait_loaded(doc).then(() => mo.disconnect());

    }

}

/*

 * Normally, we block scripts with CSP. However, Mozilla does optimizations that

 * cause part of the DOM to be loaded when our content scripts get to run. Thus,

 * before the CSP rules we inject (for non-HTTP pages) become effective, we need

 * to somehow block the execution of `<script>'s and intrinsics that were

 * already there. Additionally, some browsers (IceCat 60) seem to have problems

 * applying this CSP to non-inline `<scripts>' in certain scenarios.

 */

function prevent_script_execution(event)

{

    if (!event.target.haketilo_payload)

	event.preventDefault();

}

function mozilla_initial_block(doc)

{

    doc.addEventListener("beforescriptexecute", prevent_script_execution);

    for (const elem of doc.querySelectorAll("*")) {

	[...elem.attributes].map(attr => attr.localName)

	    .filter(attr => /^on/.test(attr) && elem.wrappedJSObject[attr])

	    .forEach(attr => elem.wrappedJSObject[attr] = null);

    }

}

/*

 * Here we block all scripts of a document which might be either and

 * HTMLDocument or an XMLDocument. Modifying an XML document might disrupt

 * Mozilla's XML preview. This is an unfortunate thing we have to accept for

 * now. XML documents *have to* be sanitized as well because they might

 * contain `<script>' tags (or on* attributes) with namespace declared as

 * "http://www.w3.org/1999/xhtml" or "http://www.w3.org/2000/svg" which allows

 * javascript execution.

 */

async function sanitize_document(doc, policy)

{

    /*

     * Blocking of scripts that are in the DOM from the beginning. Needed for

     * Mozilla.

     */

    if (is_mozilla)

	mozilla_initial_block(doc);

    /*

     * Ensure our CSP rules are employed from the beginning. This CSP injection

     * method is, when possible, going to be applied together with CSP rules

     * injected using webRequest.

     * Using elements namespaced as HTML makes this CSP injection also work for

     * non-HTML documents.

     */

    const html = new DOMParser().parseFromString(`<html><head><meta \

http-equiv="Content-Security-Policy" content="${make_csp_rule(policy)}"\

/></head><body>Loading...</body></html>`, "text/html").documentElement;

    /*

     * Root node gets hijacked now, to be re-attached after <head> is loaded

     * and sanitized.

     */

    const root = doc.documentElement;

    root.replaceWith(html);

    /*

     * When we don't inject payload, we neither block document's CSP `<meta>'

     * tags nor wait for `<head>' to be parsed.

     */

    if (policy.has_payload) {

	await wait_for_head(doc, root);

	root.querySelectorAll("head meta")

	    .forEach(m => sanitize_meta(m, policy));

    }

    root.querySelectorAll("script").forEach(s => sanitize_script(s, policy));

    html.replaceWith(root);

    root.querySelectorAll("script").forEach(s => desanitize_script(s, policy));

    start_data_urls_sanitizing(doc);

}

async function disable_service_workers()

{

    if (!navigator.serviceWorker)

	return;

    const registrations = await navigator.serviceWorker.getRegistrations();

    if (registrations.length === 0)

	return;

    console.warn("Service Workers detected on this page! Unregistering and reloading");

    try {

	await Promise.all(registrations.map(r => r.unregister()));

    } finally {

	location.reload();

    }

    /* Never actually return! */

    return new Promise(() => 0);

}

if (!is_privileged_url(document.URL)) {

    let policy_received_callback = () => undefined;

    let policy;

    /* Signature valid for half an hour. */

    const min_time = new Date().getTime() - 1800 * 1000;

    if (/^https?:/.test(document.URL)) {

	let signatures;

	[policy, signatures] = extract_cookie_policy(document.cookie, min_time);

	for (const signature of signatures)

	    document.cookie = `haketilo-${signature}=; Max-Age=-1;`;

    } else {

	const scheme = /^([^:]*)/.exec(document.URL)[1];

	const known_scheme = ["file", "ftp"].includes(scheme);

	if (!known_scheme)

	    console.warn(`Unknown url scheme: \`${scheme}'!`);

	let original_url;

	[policy, original_url] = extract_url_policy(document.URL, min_time);

	history.replaceState(null, "", original_url);

	if (known_scheme && !policy)

	    policy_received_callback = employ_nonhttp_policy;

    }

    if (!policy) {

	console.debug("Using fallback policy!");

	policy = {allow: false, nonce: gen_nonce()};

    }

    if (!(document instanceof HTMLDocument))

	policy.has_payload = false;

    console.debug("current policy", policy);

    const doc_ready = Promise.all([

	policy.allow ? Promise.resolve() : sanitize_document(document, policy),

	policy.allow ? Promise.resolve() : disable_service_workers(),

	wait_loaded(document)

    ]);

    handle_page_actions(policy.nonce, policy_received_callback, doc_ready);

    start_activity_info_server();

}