From: csteipp <csteipp@wikimedia.org>
Date: Fri, 14 Feb 2014 01:18:40 +0000 (-0800)
Subject: SECURITY: Make token comparison constant time
X-Git-Tag: 1.31.0-rc.0~16803^2
X-Git-Url: http://git.cyclocoop.org/%40spipnet%40?a=commitdiff_plain;h=74ce391e9c115320e74c06772ee4fcb610ae33c4;p=lhc%2Fweb%2Fwiklou.git

SECURITY: Make token comparison constant time

It seems like our token comparison would be vulnerable to timing
attacks. This will take constant time.

Bug: 61346
Change-Id: I2a9e89120f7092015495e638c6fa9f67adc9b84f
---

diff --git a/includes/User.php b/includes/User.php
index 4b57dd2964..0b28f664ad 100644
--- a/includes/User.php
+++ b/includes/User.php
@@ -1056,7 +1056,8 @@ class User {
 			# Get the token from DB/cache and clean it up to remove garbage padding.
 			# This deals with historical problems with bugs and the default column value.
 			$token = rtrim( $proposedUser->getToken( false ) ); // correct token
-			$passwordCorrect = ( strlen( $token ) && $token === $request->getCookie( 'Token' ) );
+			// Make comparison in constant time (bug 61346)
+			$passwordCorrect = strlen( $token ) && $this->compareSecrets( $token, $request->getCookie( 'Token' ) );
 			$from = 'cookie';
 		} else {
 			// No session or persistent login cookie
@@ -1075,6 +1076,25 @@ class User {
 		}
 	}
 
+	/**
+	 * A comparison of two strings, not vulnerable to timing attacks
+	 * @param string $answer the secret string that you are comparing against.
+	 * @param string $test compare this string to the $answer.
+	 * @return bool True if the strings are the same, false otherwise
+	 */
+	protected function compareSecrets( $answer, $test ) {
+		if ( strlen( $answer ) !== strlen( $test ) ) {
+			$passwordCorrect = false;
+		} else {
+			$result = 0;
+			for ( $i = 0; $i < strlen( $answer ); $i++ ) {
+				$result |= ord( $answer{$i} ) ^ ord( $test{$i} );
+			}
+			$passwordCorrect = ( $result == 0 );
+		}
+		return $passwordCorrect;
+	}
+
 	/**
 	 * Load user and user_group data from the database.
 	 * $this->mId must be set, this is how the user is identified.