Use URL-based policy smuggling

Increase the power of URL-based smuggling by making it (effectively)
compulsory in all cases and adapting a <salt><unique value><JSON-encoded
settings> structure. While the details still need to be worked out, the
potential for future expansion is there.

1 files changed, 34 insertions, 2 deletions

diff --git a/common/misc.js b/common/misc.js
index 8b56e79..825a117 100644
--- a/common/misc.js
+++ b/common/misc.js
@@ -2,6 +2,7 @@
  * Myext miscellaneous operations refactored to a separate file
  *
  * Copyright (C) 2021 Wojtek Kosior
+ * Copyright (C) 2021 jahoti
  * Redistribution terms are gathered in the `copyright' file.
  */
 
@@ -14,6 +15,14 @@
  * 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
@@ -26,9 +35,9 @@ function gen_unique(url)
 function get_secure_salt()
 {
     if (is_chrome)
-	return browser.runtime.getManifest().key.substring(0, 50);
+	return browser.runtime.getManifest().key.substring(0, 36);
     else
-	return browser.runtime.getURL("dummy");
+	return browser.runtime.getURL("dummy").substr(16, 36);
 }
 
 /*
@@ -95,11 +104,34 @@ function is_privileged_url(url)
     return !!/^(chrome(-extension)?|moz-extension):\/\/|^about:/i.exec(url);
 }
 
+/* Extract any policy present in the URL */
+function url_extract_policy(url)
+{
+    const targets = url_extract_target(url);
+    const key = '#' + get_secure_salt();
+    targets.sig = key + gen_unique(targets.base_url);
+    
+    if (targets.target && targets.target.startsWith(key)) {
+	targets.signed = true;
+	if (targets.target.startsWith(targets.sig))
+	    try {
+		const policy_string = targets.target.substring(101);
+		targets.policy = JSON.parse(decodeURIComponent(policy_string));
+	    } catch (e) {
+		/* TODO what should happen here? */
+	    }
+    }
+
+    return targets;
+}
+
 /*
  * EXPORTS_START
+ * EXPORT gen_nonce
  * EXPORT gen_unique
  * EXPORT url_item
  * EXPORT url_extract_target
+ * EXPORT url_extract_policy
  * EXPORT csp_rule
  * EXPORT nice_name
  * EXPORT open_in_settings