path: root/common/misc.js

/**
 * Hachette miscellaneous operations refactored to a separate file
 *
 * Copyright (C) 2021 Wojtek Kosior
 * Copyright (C) 2021 jahoti
 * Redistribution terms are gathered in the `copyright' file.
 */

/*
 * IMPORTS_START
 * IMPORT sha256
 * IMPORT browser
 * IMPORT is_chrome
 * IMPORT TYPE_NAME
 * IMPORT TYPE_PREFIX
 * IMPORTS_END
 */

/* Generate a random base64-encoded 128-bit sequence */
function gen_nonce()
{
    let randomData = new Uint8Array(16);
    crypto.getRandomValues(randomData);
    return btoa(String.fromCharCode.apply(null, randomData));
}

/*
 * generating unique, per-site value that can be computed synchronously
 * and is impossible to guess for a malicious website
 */

/* Uint8toHex is a separate function not exported as (a) it's useful and (b) it will be used in crypto.subtle-based digests */
function Uint8toHex(data)
{
    let returnValue = '';
    for (let byte of data)
	returnValue += ('00' + byte.toString(16)).slice(-2);
    return returnValue;
}

function gen_nonce(length) // Default 16
{
    let randomData = new Uint8Array(length || 16);
    crypto.getRandomValues(randomData);
    return Uint8toHex(randomData);
}

function gen_unique(url)
{
    return sha256(get_secure_salt() + url);
}

function get_secure_salt()
{
    if (is_chrome)
	return browser.runtime.getManifest().key.substring(0, 50);
    else
	return browser.runtime.getURL("dummy");
}

/*
 * stripping url from query and target (everything after `#' or `?'
 * gets removed)
 */
function url_item(url)
{
    let url_re = /^([^?#]*).*$/;
    let match = url_re.exec(url);
    return match[1];
}

/*
 * Assume a url like:
 *     https://example.com/green?illuminati=confirmed#<injected-policy>#winky
 * This function will make it into an object like:
 * {
 *     "base_url": "https://example.com/green?illuminati=confirmed",
 *     "target":   "#<injected-policy>",
 *     "target2":  "#winky",
 *     "policy":   <injected-policy-as-js-object>,
 *     "current":  <boolean-indicating-whether-policy-url-matches>
 * }
 * In case url doesn't have 2 #'s, target2 and target can be set to undefined.
 */
function url_extract_target(url)
{
    const url_re = /^([^#]*)((#[^#]*)(#.*)?)?$/;
    const match = url_re.exec(url);
    const targets  = {
	base_url: match[1],
	target:   match[3] || "",
	target2:  match[4] || ""
    };
    if (!targets.target)
	return targets;

    /* %7B -> { */
    const index = targets.target.indexOf('%7B');
    if (index === -1)
	return targets;

    const now = new Date();
    const sig = targets.target.substring(1, index);
    const policy = targets.target.substring(index);
    if (sig !== sign_policy(policy, now) &&
	sig !== sign_policy(policy, now, -1))
	return targets;

    try {
	targets.policy = JSON.parse(decodeURIComponent(policy));
	targets.current = targets.policy.base_url === targets.base_url;
    } catch (e) {
	/* This should not be reached - it's our self-produced valid JSON. */
	console.log("Unexpected internal error - invalid JSON smuggled!", e);
    }

    return targets;
}

/* csp rule that blocks all scripts except for those injected by us */
function csp_rule(nonce)
{
    let rule = `script-src 'nonce-${nonce}';`;
    if (is_chrome)
	rule += `script-src-elem 'nonce-${nonce}';`;
    return rule;
}

/*
 * Print item together with type, e.g.
 * nice_name("s", "hello") → "hello (script)"
 */
function nice_name(prefix, name)
{
    return `${name} (${TYPE_NAME[prefix]})`;
}

/* Open settings tab with given item's editing already on. */
function open_in_settings(prefix, name)
{
    name = encodeURIComponent(name);
    const url = browser.runtime.getURL("html/options.html#" + prefix + name);
    window.open(url, "_blank");
}

/* Check if url corresponds to a browser's special page */
function is_privileged_url(url)
{
    return !!/^(chrome(-extension)?|moz-extension):\/\/|^about:/i.exec(url);
}

/* Sign a given policy for a given time */
function sign_policy(policy, now, hours_offset) {
    let time = Math.floor(now / 3600000) + (hours_offset || 0);
    return gen_unique(time + policy);
}

/* Parse a CSP header */
function parse_csp(csp) {
    let directive, directive_array;
    let directives = {};
    for (directive of csp.split(';')) {
	directive = directive.trim();
	if (directive === '')
	    continue;

	directive_array = directive.split(/\s+/);
	directive = directive_array.shift();
	/* The "true" case should never occur; nevertheless... */
	directives[directive] = directive in directives ?
	    directives[directive].concat(directive_array) :
	    directive_array;
    }
    return directives;
}

/* Make CSP headers do our bidding, not interfere */
function sanitize_csp_header(header, rule, block)
{
    const csp = parse_csp(header.value);

    if (block) {
	/* No snitching */
	delete csp['report-to'];
	delete csp['report-uri'];

	delete csp['script-src'];
	delete csp['script-src-elem'];

	csp['script-src-attr'] = ["'none'"];
	csp['prefetch-src'] = ["'none'"];
    }

    if ('script-src' in csp)
	csp['script-src'].push(rule);
    else
	csp['script-src'] = [rule];

    if ('script-src-elem' in csp)
	csp['script-src-elem'].push(rule);
    else
	csp['script-src-elem'] = [rule];

    const new_policy = Object.entries(csp).map(
	i => `${i[0]} ${i[1].join(' ')};`
    );

    return {name: header.name, value: new_policy.join('')};
}

/* Regexes and objest to use as/in schemas for parse_json_with_schema(). */
const nonempty_string_matcher = /.+/;

const matchers = {
    sha256: /^[0-9a-f]{64}$/,
    nonempty_string: nonempty_string_matcher,
    component: [
	new RegExp(`^[${TYPE_PREFIX.SCRIPT}${TYPE_PREFIX.BAG}]$`),
	nonempty_string_matcher
    ]
};

/*
 * EXPORTS_START
 * EXPORT gen_nonce
 * EXPORT gen_unique
 * EXPORT url_item
 * EXPORT url_extract_target
 * EXPORT sign_policy
 * EXPORT csp_rule
 * EXPORT nice_name
 * EXPORT open_in_settings
 * EXPORT is_privileged_url
 * EXPORT sanitize_csp_header
 * EXPORT matchers
 * EXPORTS_END
 */