From ecb787046271de708b94da70240713e725299d86 Mon Sep 17 00:00:00 2001
From: jahoti <jahoti@tilde.team>
Date: Sun, 18 Jul 2021 00:00:00 +0000
Subject: Streamline and harden unique values/settings

The base URL is now included in the settings. The unique value no longer uses
it directly, as it is included by virtue of the settings; however, the number
of full hours since the epoch (UTC) is now incorporated.
---
 background/policy_injector.js | 21 +++++++++++++--------
 common/misc.js                | 34 ++++++++++++++++++++++++++--------
 content/main.js               |  2 +-
 3 files changed, 40 insertions(+), 17 deletions(-)

diff --git a/background/policy_injector.js b/background/policy_injector.js
index 8a767fb..2cd7b6e 100644
--- a/background/policy_injector.js
+++ b/background/policy_injector.js
@@ -17,6 +17,7 @@
  * IMPORT gen_nonce
  * IMPORT url_item
  * IMPORT url_extract_policy
+ * IMPORT sign_policy
  * IMPORT get_query_best
  * IMPORT csp_rule
  * IMPORTS_END
@@ -46,7 +47,7 @@ function is_our_header(header, rule)
 function url_inject(details)
 {
     const targets = url_extract_policy(details.url);
-    if (targets.valid_sig) {
+    if (targets.current) {
 	return;
     } else if (targets.policy) {
 	/* Redirect; update policy */
@@ -59,11 +60,16 @@ function url_inject(details)
 	/* Defaults */
 	settings = {};
     
-    const policy = {allow: settings.allow, nonce: gen_nonce()};
-    const policy_string = encodeURIComponent(JSON.stringify(policy));
-    const sig = gen_unique(policy_string + targets.base_url);
+    const policy = encodeURIComponent(
+	JSON.stringify({
+	    allow: settings.allow,
+	    nonce: gen_nonce(),
+	    base_url: targets.base_url
+	})
+    );
     
-    let redirect_url = targets.base_url + '#' + sig + policy_string;
+    let redirect_url = targets.base_url;
+    redirect_url += '#' + sign_policy(policy, new Date()) + policy;
     if (targets.target)
 	redirect_url += targets.target;
     if (targets.target2)
@@ -75,12 +81,11 @@ function url_inject(details)
 function inject(details)
 {
     const targets = url_extract_policy(details.url);
-    if (!targets.valid_sig)
-	/* Block unsigned requests */
+    if (!targets.current)
+	/* Block mis-/unsigned requests */
 	return {cancel: true};
 
     const rule = csp_rule(targets.policy.nonce);
-
     var headers = details.responseHeaders;
 
     if (!targets.policy.allow || is_mozilla)
diff --git a/common/misc.js b/common/misc.js
index 036eb45..472620e 100644
--- a/common/misc.js
+++ b/common/misc.js
@@ -104,23 +104,40 @@ 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);
+}
+
 /* Extract any policy present in the URL */
 function url_extract_policy(url)
 {
-    var policy_string;
     const targets = url_extract_target(url);
+    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) &&
+	sig !== sign_policy(policy, now, 1)
+    )
+	return targets;
     
     try {
-	policy_string = targets.target.substring(65);
-	targets.policy = JSON.parse(decodeURIComponent(policy_string));
+	targets.policy = JSON.parse(decodeURIComponent(policy));
+	targets.current = targets.policy.base_url === targets.base_url;
     } catch (e) {
 	/* TODO what should happen here? */
     }
-    
-    if (targets.policy) {
-	const sig = gen_unique(policy_string + targets.base_url);
-	targets.valid_sig = targets.target.substring(1, 65) === sig;
-    }
 
     return targets;
 }
@@ -132,6 +149,7 @@ function url_extract_policy(url)
  * EXPORT url_item
  * EXPORT url_extract_target
  * EXPORT url_extract_policy
+ * EXPORT sign_policy
  * EXPORT csp_rule
  * EXPORT nice_name
  * EXPORT open_in_settings
diff --git a/content/main.js b/content/main.js
index 317b319..a5e04fd 100644
--- a/content/main.js
+++ b/content/main.js
@@ -107,7 +107,7 @@ if (!is_privileged_url(document.URL)) {
 	    history.replaceState(null, "", targets.base_url);
     }
     
-    targets.policy = targets.valid_sig ? targets.policy : {};
+    targets.policy = targets.current ? targets.policy : {};
     
     const nonce = targets.policy.nonce || gen_nonce();
     start_activity_info_server();
-- 
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