Haketilo

/**

 * This file is part of Haketilo.

 *

 * Function: Modify HTTP traffic usng webRequest API.

 *

 * Copyright (C) 2021, 2022 Wojtek Kosior <koszko@koszko.org>

 *

 * 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 of this code in a

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

 */

#IMPORT common/indexeddb.js AS haketilodb

#IF MOZILLA

#IMPORT background/stream_filter.js

#ENDIF

#FROM common/browser.js IMPORT browser

#FROM common/misc.js    IMPORT is_privileged_url, csp_header_regex, \

                               sha256_async AS sha256

#FROM common/policy.js  IMPORT decide_policy

#FROM background/patterns_query_manager.js IMPORT tree, default_allow

let secret;

#IF MOZILLA

/*

 * Under Mozilla-based browsers, responses are cached together with headers as

 * they appear *after* modifications by Haketilo. This means Haketilo's CSP

 * script-blocking headers might be present in responses loaded from cache. In

 * the meantime the user might have changes Haketilo settings to instead allow

 * the scripts on the page in question. This causes a problem and creates the

 * need to somehow restore the response headers to the state in which they

 * arrived from the server.

 * To cope with this, Haketilo will inject some additional headers with private

 * data. Those will include a hard-to-guess value derived from extension's

 * internal ID. It is assumed the internal ID has a longer lifetime than cached

 * responses.

 */

const settings_page_url = browser.runtime.getURL("html/settings.html");

const header_prefix_prom = sha256(settings_page_url)

      .then(hash => `X-Haketilo-${hash}`);

/*

 * Mozilla, unlike Chrome, allows webRequest callbacks to return promises. Here

 * we leverage that to be able to use asynchronous sha256 computation.

 */

async function on_headers_received(details) {

#IF NEVER

} /* Help auto-indent in editors. */

#ENDIF

#ELSE

function on_headers_received(details) {

#ENDIF

    const url = details.url;

    if (is_privileged_url(details.url))

	return;

    let headers = details.responseHeaders;

#IF MOZILLA

    const prefix = await header_prefix_prom;

    /*

     * We assume that the original CSP headers of a response are always

     * preserved under names of the form:

     *     X-Haketilo-<some_secret>-<original_name>

     * In some cases the original response may contain no CSP headers. To still

     * be able to tell whether the headers we were provided were modified by

     * Haketilo in the past, all modifications are accompanied by addition of an

     * extra header with name:

     *     X-Haketilo-<some_secret>

     */

    const restore_old_headers = details.fromCache &&

	  !!headers.filter(h => h.name === prefix).length;

    if (restore_old_headers) {

	const restored_headers = [];

	for (const h of headers) {

	    if (csp_header_regex.test(h.name) || h.name === prefix)

		continue;

	    if (h.name.startsWith(prefix)) {

		restored_headers.push({

		    name:  h.name.substring(prefix.length + 1),

		    value: h.value

		});

	    } else {

		restored_headers.push(h);

	    }

	}

	headers = restored_headers;

    }

#ENDIF

    const policy =

	  decide_policy(tree, details.url, !!default_allow.value, secret);

    if (!policy.allow) {

#IF MOZILLA

	const to_append = [{name: prefix, value: ":)"}];

	for (const h of headers.filter(h => csp_header_regex.test(h.name))) {

	    if (!policy.payload)

		to_append.push(Object.assign({}, h));

	    h.name = `${prefix}-${h.name}`;

	}

	headers.push(...to_append);

#ELSE

	if (policy.payload)

	    headers = headers.filter(h => !csp_header_regex.test(h.name));

#ENDIF

	headers.push({name: "Content-Security-Policy", value: policy.csp});

    }

#IF MOZILLA

    /*

     * When page is meant to be viewed in the browser, use streamFilter to

     * inject a dummy <script> at the very beginning of it. This <script>

     * will cause extension's content scripts to run before page's first <meta>

     * tag is rendered so that they can prevent CSP rules inside <meta> tags

     * from blocking the payload we want to inject.

     */

    let use_stream_filter = !!policy.payload;

    if (use_stream_filter) {

	for (const header of headers) {

	    if (header.name.toLowerCase().trim() !== "content-disposition")

		continue;

	    if (/^\s*attachment\s*(;.*)$/i.test(header.value)) {

		use_stream_filter = false;

	    } else {

		use_stream_filter = true;

		break;

	    }

	}

    }

    use_stream_filter = use_stream_filter &&

	(details.statusCode < 300 || details.statusCode >= 400);

    if (use_stream_filter)

	headers = stream_filter.apply(details, headers, policy);

#ENDIF

    return {responseHeaders: headers};

}

#IF CHROMIUM && MV2

const request_url_regex = /^[^?]*\?url=(.*)$/;

const redirect_url_template = browser.runtime.getURL("dummy") + "?settings=";

function on_before_request(details)

{

    /*

     * Content script will make a synchronous XmlHttpRequest to extension's

     * `dummy` file to query settings for given URL. We smuggle that

     * information in query parameter of the URL we redirect to.

     * A risk of fingerprinting arises if a page with script execution allowed

     * guesses the dummy file URL and makes an AJAX call to it. It is currently

     * a problem in ManifestV2 Chromium-family port of Haketilo because Chromium

     * uses predictable URLs for web-accessible resources. We plan to fix it in

     * the future ManifestV3 port.

     */

    if (details.type !== "xmlhttprequest")

	return {cancel: true};

    if (details.url.startsWith(redirect_url_template))

	return;

#IF DEBUG

    console.debug(`Haketilo: Settings queried using XHR for '${details.url}'.`);

#ENDIF

    /*

     * request_url should be of the following format:

     *     <url_for_extension's_dummy_file>?url=<valid_urlencoded_url>

     */

    const match = request_url_regex.exec(details.url);

    if (match) {

	const queried_url = decodeURIComponent(match[1]);

	if (details.initiator && details.initiator !== "null" &&

	    !queried_url.startsWith(details.initiator)) {

	    console.warn(`Haketilo: Blocked suspicious query of '${queried_url}' by '${details.initiator}'. This might be the result of page fingerprinting the browser.`);

	    return {cancel: true};

	}

	const policy =

	      decide_policy(tree, queried_url, !!default_allow.value, secret);

	if (!policy.error) {

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

	    return {redirectUrl: redirect_url_template + encoded_policy};

	}

    }

    console.warn(`Haketilo: Bad request! Expected ${browser.runtime.getURL("dummy")}?url=<valid_urlencoded_url>. Got ${details.url}. This might be the result of page fingerprinting the browser.`);

    return {cancel: true};

}

const all_types = [

    "main_frame", "sub_frame", "stylesheet", "script", "image", "font",

    "object", "xmlhttprequest", "ping", "csp_report", "media", "websocket",

    "other", "main_frame", "sub_frame"

];

#ENDIF

async function start(secret_)

{

    secret = secret_;

#IF CHROMIUM

    const extra_opts = ["blocking", "extraHeaders"];

#ELSE

    const extra_opts = ["blocking"];

#ENDIF

    browser.webRequest.onHeadersReceived.addListener(

	on_headers_received,

	{urls: ["<all_urls>"], types: ["main_frame", "sub_frame"]},

	extra_opts.concat("responseHeaders")

    );

#IF CHROMIUM && MV2

    browser.webRequest.onBeforeRequest.addListener(

	on_before_request,

	{urls: [browser.runtime.getURL("dummy") + "*"], types: all_types},

	extra_opts

    );

#ENDIF

}

#EXPORT start