0001-SECURITY-API-Use-constant-time-comparison-for-watchl.patch
demon (Chad Horohoe)
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	• demon
	Aug 10 2015, 7:37 PM

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0001-SECURITY-API-Use-constant-time-comparison-for-watchl.patch
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	From ef942c1cfc2b75cdaca47d96ce3bd53e3fb3d9da Mon Sep 17 00:00:00 2001
	From: Chad Horohoe <chadh@wikimedia.org>
	Date: Mon, 10 Aug 2015 12:33:18 -0700
	Subject: [PATCH] SECURITY: API: Use constant-time comparison for watchlist
	token

	Avoids a theoretical timing attack.

	Includes backport of hash_equals() compat function from Iece006e

	Bug: T94116
	Change-Id: Ia4a2b13bd5d3cd256c6b2deada224148dc2888a6
	---
	includes/GlobalFunctions.php \| 47 ++++++++++++++++++++++++++++++++++++++++++++
	includes/api/ApiBase.php \| 2 +-
	2 files changed, 48 insertions(+), 1 deletion(-)

	diff --git a/includes/GlobalFunctions.php b/includes/GlobalFunctions.php
	index c292892..8941b97 100644
	--- a/includes/GlobalFunctions.php
	+++ b/includes/GlobalFunctions.php
	@@ -104,6 +104,53 @@ if ( !function_exists( 'gzdecode' ) ) {
	return gzinflate( substr( $data, 10, -8 ) );
	}
	}
	+
	+// hash_equals function only exists in PHP >= 5.6.0
	+if ( !function_exists( 'hash_equals' ) ) {
	+ /**
	+ * Check whether a user-provided string is equal to a fixed-length secret without
	+ * revealing bytes of the secret through timing differences.
	+ *
	+ * This timing guarantee -- that a partial match takes the same time as a complete
	+ * mismatch -- is why this function is used in some security-sensitive parts of the code.
	+ * For example, it shouldn't be possible to guess an HMAC signature one byte at a time.
	+ *
	+ * Longer explanation: http://www.emerose.com/timing-attacks-explained
	+ *
	+ * @codeCoverageIgnore
	+ * @param string $known_string Fixed-length secret to compare against
	+ * @param string $user_string User-provided string
	+ * @return bool True if the strings are the same, false otherwise
	+ */
	+ function hash_equals( $known_string, $user_string ) {
	+ // Strict type checking as in PHP's native implementation
	+ if ( !is_string( $known_string ) ) {
	+ trigger_error( 'hash_equals(): Expected known_string to be a string, ' .
	+ gettype( $known_string ) . ' given', E_USER_WARNING );
	+
	+ return false;
	+ }
	+
	+ if ( !is_string( $user_string ) ) {
	+ trigger_error( 'hash_equals(): Expected user_string to be a string, ' .
	+ gettype( $user_string ) . ' given', E_USER_WARNING );
	+
	+ return false;
	+ }
	+
	+ // Note that we do one thing PHP doesn't: try to avoid leaking information about
	+ // relative lengths of $known_string and $user_string, and of multiple $known_strings.
	+ // However, lengths may still inevitably leak through, for example, CPU cache misses.
	+ $known_string_len = strlen( $known_string );
	+ $user_string_len = strlen( $user_string );
	+ $result = $known_string_len ^ $user_string_len;
	+ for ( $i = 0; $i < $user_string_len; $i++ ) {
	+ $result \|= ord( $known_string[$i % $known_string_len] ) ^ ord( $user_string[$i] );
	+ }
	+
	+ return ( $result === 0 );
	+ }
	+}
	/// @endcond

	/**
	diff --git a/includes/api/ApiBase.php b/includes/api/ApiBase.php
	index 7b91952..8aec787 100644
	--- a/includes/api/ApiBase.php
	+++ b/includes/api/ApiBase.php
	@@ -2079,7 +2079,7 @@ abstract class ApiBase extends ContextSource {
	$this->dieUsage( 'Specified user does not exist', 'bad_wlowner' );
	}
	$token = $user->getOption( 'watchlisttoken' );
	- if ( $token == '' \|\| $token != $params['token'] ) {
	+ if ( $token == '' \|\| !hash_equals( $token, $params['token'] ) ) {
	$this->dieUsage(
	'Incorrect watchlist token provided -- please set a correct token in Special:Preferences',
	'bad_wltoken'
	--
	2.4.6

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0001-SECURITY-API-Use-constant-time-comparison-for-watchl.patch
demon (Chad Horohoe)
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0001-SECURITY-API-Use-constant-time-comparison-for-watchl.patch
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