File rubygem-actionpack-2.1.2_timing_weakness.patch of Package rubygem-actionpack-2_1

From 674f780d59a5a7ec0301755d43a7b277a3ad2978 Mon Sep 17 00:00:00 2001
From: Michael Koziarski <michael@koziarski.com>
Date: Sun, 23 Aug 2009 17:26:46 +1200
Subject: [PATCH] Fix timing attack vulnerability in the Cookie Store

Use a constant-time comparison algorithm to compare the candidate HMAC with the calculated HMAC to prevent leaking information about the calculated HMAC
---
 .../lib/action_controller/session/cookie_store.rb  |   15 ++++++++++++++-
 1 files changed, 14 insertions(+), 1 deletions(-)

Index: lib/action_controller/session/cookie_store.rb
===================================================================
--- lib/action_controller/session/cookie_store.rb.orig	1970-01-01 01:00:00.000000000 +0100
+++ lib/action_controller/session/cookie_store.rb	2009-09-16 15:04:36.743029435 +0200
@@ -139,7 +139,7 @@ class CGI::Session::CookieStore
         data, digest = cookie.split('--')
 
         # Do two checks to transparently support old double-escaped data.
-        unless digest == generate_digest(data) || digest == generate_digest(data = CGI.unescape(data))
+        unless secure_compare(digest, generate_digest(data)) || secure_compare(digest, generate_digest(data = CGI.unescape(data)))
           delete
           raise TamperedWithCookie
         end
@@ -163,4 +163,17 @@ class CGI::Session::CookieStore
     def clear_old_cookie_value
       @session.cgi.cookies[@cookie_options['name']].clear
     end
+
+    # constant-time comparison algorithm to prevent timing attacks
+    def secure_compare(a, b)
+      if a.length == b.length
+        result = 0
+        for i in 0..(a.length - 1)
+          result |= a[i] ^ b[i]
+        end
+        result == 0
+      else
+        false
+      end
+    end
 end