From: Tim Starling <tstarling@users.mediawiki.org>
Date: Thu, 16 Feb 2012 23:27:00 +0000 (+0000)
Subject: (bug 34428) Fixed hash mismatch errors in DiffHistoryBlob::patch() by simulating... 
X-Git-Tag: 1.31.0-rc.0~24659
X-Git-Url: http://git.cyclocoop.org/%24image?a=commitdiff_plain;h=e1ee5c469b685cbdb345f2cfcbef66855e05a01a;p=lhc%2Fweb%2Fwiklou.git

(bug 34428) Fixed hash mismatch errors in DiffHistoryBlob::patch() by simulating LibXDiff's broken Adler-32 implementation.
---

diff --git a/RELEASE-NOTES-1.20 b/RELEASE-NOTES-1.20
index bb894f86e5..5090672bdf 100644
--- a/RELEASE-NOTES-1.20
+++ b/RELEASE-NOTES-1.20
@@ -29,6 +29,8 @@ production.
 * (bug 12021) Added user talk link on Special:Listusers
 * (bug 34445) section edit and TOC hide/show links are excluded from selection and
   copy/paste on supporting browsers
+* (bug 34428) Fixed incorrect hash mismatch errors in the DiffHistoryBlob 
+  history compression method.
 
 === API changes in 1.20 ===
 * (bug 34316) Add ability to retrieve maximum upload size from MediaWiki API.
diff --git a/includes/HistoryBlob.php b/includes/HistoryBlob.php
index cece3ec1fa..7887ff85d9 100644
--- a/includes/HistoryBlob.php
+++ b/includes/HistoryBlob.php
@@ -515,14 +515,11 @@ class DiffHistoryBlob implements HistoryBlob {
 
 		$header = unpack( 'Vofp/Vcsize', substr( $diff, 0, 8 ) );
 		
-		# Check the checksum if mhash is available
-		if ( extension_loaded( 'mhash' ) ) {
-			$ofp = mhash( MHASH_ADLER32, $base );
-			if ( $ofp !== substr( $diff, 0, 4 ) ) {
-				wfDebug( __METHOD__. ": incorrect base checksum\n" );
-				// Temp patch for bug 34428: don't return false
-				//return false;
-			}
+		# Check the checksum if hash/mhash is available
+		$ofp = $this->xdiffAdler32( $base );
+		if ( $ofp !== false && $ofp !== substr( $diff, 0, 4 ) ) {
+			wfDebug( __METHOD__. ": incorrect base checksum\n" );
+			return false;
 		}
 		if ( $header['csize'] != strlen( $base ) ) {
 			wfDebug( __METHOD__. ": incorrect base length\n" );
@@ -561,6 +558,29 @@ class DiffHistoryBlob implements HistoryBlob {
 		return $out;
 	}
 
+	/**
+	 * Compute a binary "Adler-32" checksum as defined by LibXDiff, i.e. with 
+	 * the bytes backwards and initialised with 0 instead of 1. See bug 34428.
+	 *
+	 * Returns false if no hashing library is available
+	 */
+	function xdiffAdler32( $s ) {
+		static $init;
+		if ( $init === null ) {
+			// The real Adler-32 checksum of this string is zero, so it 
+			// initialises the state to the LibXDiff initial value.
+			$init = str_repeat( "\xf0", 205 ) . "\xee" . str_repeat( "\xf0", 67 ) . "\x02";
+		}
+		if ( function_exists( 'hash' ) ) {
+			$hash = hash( 'adler32', $init . $s, true );
+		} elseif ( function_exists( 'mhash' ) ) {
+			$hash = mhash( MHASH_ADLER32, $init . $s );
+		} else {
+			return false;
+		}
+		return strrev( $hash );
+	}
+
 	function uncompress() {
 		if ( !$this->mDiffs ) {
 			return;
diff --git a/tests/phpunit/includes/DiffHistoryBlobTest.php b/tests/phpunit/includes/DiffHistoryBlobTest.php
new file mode 100644
index 0000000000..eda55e0654
--- /dev/null
+++ b/tests/phpunit/includes/DiffHistoryBlobTest.php
@@ -0,0 +1,36 @@
+<?php
+
+class DiffHistoryBlobTest extends MediaWikiTestCase {
+	function setUp() {
+		if ( !extension_loaded( 'xdiff' ) ) {
+			$this->markTestSkipped( 'The xdiff extension is not available' );
+			return;
+		}
+		if ( !extension_loaded( 'hash' ) && !extension_loaded( 'mhash' ) ) {
+			$this->markTestSkipped( 'Neither the hash nor mhash extension is available' );
+			return;
+		}
+	}
+
+	/**
+	 * Test for DiffHistoryBlob::xdiffAdler32()
+	 * @dataProvider provideXdiffAdler32
+	 */
+	function testXdiffAdler32( $input ) {
+		$xdiffHash = substr( xdiff_string_rabdiff( $input, '' ),  0, 4 );
+		$dhb = new DiffHistoryBlob;
+		$myHash = $dhb->xdiffAdler32( $input );
+		$this->assertSame( bin2hex( $xdiffHash ), bin2hex( $myHash ),
+			"Hash of " . addcslashes( $input, "\0..\37!@\@\177..\377" ) );
+	}
+
+	function provideXdiffAdler32() {
+		return array(
+			array( '', 'Empty string' ),
+			array( "\0", 'Null' ),
+			array( "\0\0\0", "Several nulls" ),
+			array( "Hello", "An ASCII string" ),
+			array( str_repeat( "x", 6000 ), "A string larger than xdiff's NMAX (5552)" )
+		);
+	}
+}