Haketilo

/**

 * This file is part of Haketilo.

 *

 * Function: Determining what to do on a given web page.

 *

 * Copyright (C) 2021 Wojtek Kosior

 *

 * 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/patterns_query_tree.js AS pqt

#FROM common/sha256.js IMPORT sha256

/*

 * CSP rule that either blocks all scripts or only allows scripts with specified

 * nonce attached.

 */

function make_csp(nonce) {

    const rule = nonce ? `'nonce-${nonce}'` : "'none'";

    const csp_list = [

	["prefetch-src",    "'none'"],

	["script-src-attr", "'none'"],

	["script-src",      rule, "'unsafe-eval'"],

	["script-src-elem", rule]

    ];

    return csp_list.map(words => `${words.join(" ")};`).join(" ");

}

function decide_policy(patterns_tree, url, default_allow, secret)

{

    const policy = {allow: default_allow};

    try {

	var payloads = pqt.search(patterns_tree, url).next().value;

    } catch (e) {

	console.error("Haketilo:", e);

	policy.allow = false;

	policy.error = {haketilo_error_type: "deciding_policy"};

    }

    if (payloads !== undefined) {

	/*

	 * mapping will be either the actual mapping identifier or "~allow" if

	 * we matched a simple script block/allow rule.

	 */

	policy.mapping = Object.keys(payloads).sort()[0];

	const payload = payloads[policy.mapping];

	if (policy.mapping === "~allow") {

	    /* Convert 0/1 back to false/true. */

	    policy.allow = !!payload;

	} else /* if (payload.identifier) */ {

	    policy.allow = false;

	    policy.payload = payload;

	    /*

	     * Hash a secret and other values into a string that's unpredictable

	     * to someone who does not know these values. What we produce here

	     * is not a true "nonce" because it might get produced multiple

	     * times given the same url and mapping choice. Nevertheless, this

	     * is reasonably good given the limitations WebExtension APIs and

	     * environments give us. If we were using a true nonce, we'd have no

	     * reliable way of passing it to our content scripts.

	     */

	    const nonce_source = [

		policy.mapping,

		policy.payload.identifier,

		url,

		secret

	    ];

	    policy.nonce = sha256(nonce_source.join(":"));

	}

    }

    if (!policy.allow)

	policy.csp = make_csp(policy.nonce);

    return policy;

}

#EXPORT decide_policy

#EXPORT  () => ({allow: false, csp: make_csp()})  AS fallback_policy

#IF NEVER

/*

 * Note: the functions below were overeagerly written and are not used now but

 * might prove useful to once we add more functionalities and are hence kept...

 */

function relaxed_csp_eval(csp) {

    const new_csp_list = [];

    for (const directive of csp.split(";")) {

	const directive_words = directive.trim().split(" ");

	if (directive_words[0] === "script-src")

	    directive_words.push("'unsafe-eval'");

	new_csp_list.push(directive_words);

    }

    new_policy.csp = new_csp_list.map(d => `${d.join(" ")}';`).join(" ");

}

function relax_policy_eval(policy) {

    const new_policy = Object.assign({}, policy);

    return Object.assign(new_policy, {csp: relaxed_csp_eval(policy.csp)});

}

#EXPORT relax_policy_eval

#ENDIF