diff options
| -rw-r--r-- | background/main.js | 2 | ||||
| -rw-r--r-- | background/policy_injector.js | 33 | ||||
| -rw-r--r-- | common/misc.js | 38 | ||||
| -rw-r--r-- | common/signing.js | 73 | ||||
| -rw-r--r-- | content/main.js | 33 |
5 files changed, 118 insertions, 61 deletions
diff --git a/background/main.js b/background/main.js index 85f8ce8..2c8a87b 100644 --- a/background/main.js +++ b/background/main.js @@ -69,7 +69,7 @@ function on_headers_received(details) skip = true; } - headers = inject_csp_headers(details, headers, policy); + headers = inject_csp_headers(headers, policy); skip = skip || (details.statusCode >= 300 && details.statusCode < 400); if (!skip) { diff --git a/background/policy_injector.js b/background/policy_injector.js index 1d4db6f..72318d4 100644 --- a/background/policy_injector.js +++ b/background/policy_injector.js @@ -16,25 +16,27 @@ * IMPORTS_END */ -function inject_csp_headers(details, headers, policy) +function inject_csp_headers(headers, policy) { - const url = details.url; - - let orig_csp_headers; + let csp_headers; let old_signature; let hachette_header; for (const header of headers.filter(h => h.name === "x-hachette")) { - const match = /^([^%])(%.*)$/.exec(header.value); + /* x-hachette header has format: <signature>_0_<data> */ + const match = /^([^_]+)_(0_.*)$/.exec(header.value); if (!match) continue; - const old_data = extract_signed(...match.splice(1, 2), [[0]]); - if (!old_data || old_data.url !== url) + const result = extract_signed(...match.slice(1, 3)); + if (result.fail) continue; + /* This should succeed - it's our self-produced valid JSON. */ + const old_data = JSON.parse(decodeURIComponent(result.data)); + /* Confirmed- it's the originals, smuggled in! */ - orig_csp_headers = old_data.csp_headers; + csp_headers = old_data.csp_headers; old_signature = old_data.policy_sig; hachette_header = header; @@ -46,24 +48,23 @@ function inject_csp_headers(details, headers, policy) headers.push(hachette_header); } - orig_csp_headers = orig_csp_headers || + csp_headers = csp_headers || headers.filter(h => is_csp_header_name(h.name)); /* When blocking remove report-only CSP headers that snitch on us. */ headers = headers.filter(h => !is_csp_header_name(h.name, !policy.allow)); if (old_signature) - headers = headers.filter(h => h.name.search(old_signature) === -1); + headers = headers.filter(h => h.value.search(old_signature) === -1); - const sanitizer = h => sanitize_csp_header(h, policy); - headers.push(...orig_csp_headers.map(sanitizer)); + headers.push(...csp_headers.map(h => sanitize_csp_header(h, policy))); const policy_str = encodeURIComponent(JSON.stringify(policy)); - const policy_sig = sign_data(policy_str, new Date()); + const signed_policy = sign_data(policy_str, new Date().getTime()); const later_30sec = new Date(new Date().getTime() + 30000).toGMTString(); headers.push({ name: "Set-Cookie", - value: `hachette-${policy_sig}=${policy_str}; Expires=${later_30sec};` + value: `hachette-${signed_policy.join("=")}; Expires=${later_30sec};` }); /* @@ -71,9 +72,9 @@ function inject_csp_headers(details, headers, policy) * These are signed with a time of 0, as it's not clear there is a limit on * how long Firefox might retain headers in the cache. */ - let hachette_data = {csp_headers: orig_csp_headers, policy_sig, url}; + let hachette_data = {csp_headers, policy_sig: signed_policy[0]}; hachette_data = encodeURIComponent(JSON.stringify(hachette_data)); - hachette_header.value = sign_data(hachette_data, 0) + hachette_data; + hachette_header.value = sign_data(hachette_data, 0).join("_"); /* To ensure there is a CSP header if required */ if (!policy.allow) diff --git a/common/misc.js b/common/misc.js index 8894d60..d6b9662 100644 --- a/common/misc.js +++ b/common/misc.js @@ -8,9 +8,7 @@ /* * IMPORTS_START - * IMPORT sha256 * IMPORT browser - * IMPORT is_chrome * IMPORT TYPE_NAME * IMPORT TYPE_PREFIX * IMPORTS_END @@ -45,32 +43,6 @@ function gen_nonce(length) // Default 16 return Uint8toHex(randomData); } -function get_secure_salt() -{ - if (is_chrome) - return browser.runtime.getManifest().key.substring(0, 50); - else - return browser.runtime.getURL("dummy"); -} - -function extract_signed(signature, data, times) -{ - const now = new Date(); - times = times || [[now], [now, -1]]; - - const reductor = - (ok, time) => ok || signature === sign_data(data, ...time); - if (!times.reduce(reductor, false)) - return undefined; - - try { - return JSON.parse(decodeURIComponent(data)); - } catch (e) { - /* This should not be reached - it's our self-produced valid JSON. */ - console.log("Unexpected internal error - invalid JSON smuggled!", e); - } -} - /* csp rule that blocks all scripts except for those injected by us */ function csp_rule(nonce) { @@ -89,7 +61,7 @@ const report_only_header_name = "content-security-policy-report-only"; function is_csp_header_name(string, include_report_only) { - string = string && string.toLowerCase() || ""; + string = string && string.toLowerCase().trim() || ""; return (include_report_only && string === report_only_header_name) || csp_header_names.has(string); @@ -118,12 +90,6 @@ function is_privileged_url(url) return !!/^(chrome(-extension)?|moz-extension):\/\/|^about:/i.exec(url); } -/* Sign a given string for a given time */ -function sign_data(data, now, hours_offset) { - let time = Math.floor(now / 3600000) + (hours_offset || 0); - return sha256(get_secure_salt() + time + data); -} - /* Parse a CSP header */ function parse_csp(csp) { let directive, directive_array; @@ -193,8 +159,6 @@ const matchers = { /* * EXPORTS_START * EXPORT gen_nonce - * EXPORT extract_signed - * EXPORT sign_data * EXPORT csp_rule * EXPORT is_csp_header_name * EXPORT nice_name diff --git a/common/signing.js b/common/signing.js new file mode 100644 index 0000000..2171714 --- /dev/null +++ b/common/signing.js @@ -0,0 +1,73 @@ +/** + * part of Hachette + * Functions related to "signing" of data, refactored to a separate file. + * + * Copyright (C) 2021 Wojtek Kosior + * Redistribution terms are gathered in the `copyright' file. + */ + +/* + * IMPORTS_START + * IMPORT sha256 + * IMPORT browser + * IMPORT is_chrome + * IMPORTS_END + */ + +/* + * In order to make certain data synchronously accessible in certain contexts, + * hachette smuggles it in string form in places like cookies, URLs and headers. + * When using the smuggled data, we first need to make sure it isn't spoofed. + * For that, we use this pseudo-signing mechanism. + * + * Despite what name suggests, no assymetric cryptography is involved, as it + * would bring no additional benefits and would incur bigger performance + * overhead. Instead, we hash the string data together with some secret value + * that is supposed to be known only by this browser instance. Resulting hash + * sum plays the role of the signature. In the hash we also include current + * time. This way, even if signed data leaks (which shouldn't happen in the + * first place), an attacker won't be able to re-use it indefinitely. + * + * The secret shared between execution contexts has to be available + * synchronously. Under Mozilla, this is the extension's per-session id. Under + * Chromium, this is the key that resides in the manifest. + * + * An idea to (under Chromium) instead store the secret in a file fetched + * synchronously using XMLHttpRequest is being considered. + */ + +function get_secret() +{ + if (is_chrome) + return browser.runtime.getManifest().key.substring(0, 50); + else + return browser.runtime.getURL("dummy"); +} + +function extract_signed(signature, signed_data) +{ + const match = /^([1-9][0-9]{12}|0)_(.*)$/.exec(signed_data); + if (!match) + return {fail: "bad format"}; + + const result = {time: parseInt(match[1]), data: match[2]}; + if (sign_data(result.data, result.time)[0] !== signature) + result.fail = "bad signature"; + + return result; +} + +/* + * Sign a given string for a given time. Time should be either 0 or in the range + * 10^12 <= time < 10^13. + */ +function sign_data(data, time) { + return [sha256(get_secret() + time + data), `${time}_${data}`]; +} + +/* + * EXPORTS_START + * EXPORT extract_signed + * EXPORT sign_data + * EXPORTS_END + */ diff --git a/content/main.js b/content/main.js index 4ae7738..984b3cb 100644 --- a/content/main.js +++ b/content/main.js @@ -32,17 +32,36 @@ function accept_node(node, parent) } if (!is_privileged_url(document.URL)) { - const reductor = - (ac, [_, sig, pol]) => ac[0] && ac || [extract_signed(sig, pol), sig]; - const matches = [...document.cookie.matchAll(/hachette-(\w*)=([^;]*)/g)]; - let [policy, signature] = matches.reduce(reductor, []); + /* Signature valid for half an hour. */ + const min_time = new Date().getTime() - 1800 * 1000; + let best_result = {time: -1}; + let policy = null; + const extracted_signatures = []; + for (const match of document.cookie.matchAll(/hachette-(\w*)=([^;]*)/g)) { + const new_result = extract_signed(...match.slice(1, 3)); + if (new_result.fail) + continue; - if (!policy || policy.url !== document.URL) { - console.log("WARNING! Using default policy!!!"); + 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; + } + + if (!policy) { + console.warn("WARNING! Using default policy!!!"); policy = {allow: false, nonce: gen_nonce()}; } - if (signature) + for (const signature of extracted_signatures) document.cookie = `hachette-${signature}=; Max-Age=-1;`; handle_page_actions(policy.nonce); |