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authorWojtek Kosior <koszko@koszko.org>2021-08-26 11:50:36 +0200
committerWojtek Kosior <koszko@koszko.org>2021-08-26 11:50:36 +0200
commit2875397fb887a5b09b5f39d6b3a75419a516dd07 (patch)
tree36773a9bb3a60c2cb271191b7aaf2f75db5a191a
parent6b53d6c840140fc5df6d7638808b978d96502a35 (diff)
downloadbrowser-extension-2875397fb887a5b09b5f39d6b3a75419a516dd07.tar.gz
browser-extension-2875397fb887a5b09b5f39d6b3a75419a516dd07.zip
improve signing\n\nSignature timestamp is now handled in a saner way. Sha256 implementation is no longer pulled in contexts that don't require it.
-rw-r--r--background/main.js2
-rw-r--r--background/policy_injector.js33
-rw-r--r--common/misc.js38
-rw-r--r--common/signing.js73
-rw-r--r--content/main.js33
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);