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[mediawiki.git] / includes / ZipDirectoryReader.php

<?php
/**
 * ZIP file directories reader, for the purposes of upload verification.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 */

/**
 * A class for reading ZIP file directories, for the purposes of upload
 * verification.
 *
 * Only a functional interface is provided: ZipFileReader::read(). No access is
 * given to object instances.
 *
 */
class ZipDirectoryReader {
        /**
         * Read a ZIP file and call a function for each file discovered in it.
         *
         * Because this class is aimed at verification, an error is raised on
         * suspicious or ambiguous input, instead of emulating some standard
         * behavior.
         *
         * @param string $fileName The archive file name
         * @param array $callback The callback function. It will be called for each file
         *   with a single associative array each time, with members:
         *
         *      - name: The file name. Directories conventionally have a trailing
         *        slash.
         *
         *      - mtime: The file modification time, in MediaWiki 14-char format
         *
         *      - size: The uncompressed file size
         *
         * @param array $options An associative array of read options, with the option
         *    name in the key. This may currently contain:
         *
         *      - zip64: If this is set to true, then we will emulate a
         *        library with ZIP64 support, like OpenJDK 7. If it is set to
         *        false, then we will emulate a library with no knowledge of
         *        ZIP64.
         *
         *        NOTE: The ZIP64 code is untested and probably doesn't work. It
         *        turned out to be easier to just reject ZIP64 archive uploads,
         *        since they are likely to be very rare. Confirming safety of a
         *        ZIP64 file is fairly complex. What do you do with a file that is
         *        ambiguous and broken when read with a non-ZIP64 reader, but valid
         *        when read with a ZIP64 reader? This situation is normal for a
         *        valid ZIP64 file, and working out what non-ZIP64 readers will make
         *        of such a file is not trivial.
         *
         * @return Status object. The following fatal errors are defined:
         *
         *      - zip-file-open-error: The file could not be opened.
         *
         *      - zip-wrong-format: The file does not appear to be a ZIP file.
         *
         *      - zip-bad: There was something wrong or ambiguous about the file
         *        data.
         *
         *      - zip-unsupported: The ZIP file uses features which
         *        ZipDirectoryReader does not support.
         *
         * The default messages for those fatal errors are written in a way that
         * makes sense for upload verification.
         *
         * If a fatal error is returned, more information about the error will be
         * available in the debug log.
         *
         * Note that the callback function may be called any number of times before
         * a fatal error is returned. If this occurs, the data sent to the callback
         * function should be discarded.
         */
        public static function read( $fileName, $callback, $options = array() ) {
                $zdr = new self( $fileName, $callback, $options );
                return $zdr->execute();
        }

        /** The file name */
        var $fileName;

        /** The opened file resource */
        var $file;

        /** The cached length of the file, or null if it has not been loaded yet. */
        var $fileLength;

        /** A segmented cache of the file contents */
        var $buffer;

        /** The file data callback */
        var $callback;

        /** The ZIP64 mode */
        var $zip64 = false;

        /** Stored headers */
        var $eocdr, $eocdr64, $eocdr64Locator;

        var $data;

        /** The "extra field" ID for ZIP64 central directory entries */
        const ZIP64_EXTRA_HEADER = 0x0001;

        /** The segment size for the file contents cache */
        const SEGSIZE = 16384;

        /** The index of the "general field" bit for UTF-8 file names */
        const GENERAL_UTF8 = 11;

        /** The index of the "general field" bit for central directory encryption */
        const GENERAL_CD_ENCRYPTED = 13;

        /**
         * Private constructor
         */
        protected function __construct( $fileName, $callback, $options ) {
                $this->fileName = $fileName;
                $this->callback = $callback;

                if ( isset( $options['zip64'] ) ) {
                        $this->zip64 = $options['zip64'];
                }
        }

        /**
         * Read the directory according to settings in $this.
         *
         * @return Status
         */
        function execute() {
                $this->file = fopen( $this->fileName, 'r' );
                $this->data = array();
                if ( !$this->file ) {
                        return Status::newFatal( 'zip-file-open-error' );
                }

                $status = Status::newGood();
                try {
                        $this->readEndOfCentralDirectoryRecord();
                        if ( $this->zip64 ) {
                                list( $offset, $size ) = $this->findZip64CentralDirectory();
                                $this->readCentralDirectory( $offset, $size );
                        } else {
                                if ( $this->eocdr['CD size'] == 0xffffffff
                                        || $this->eocdr['CD offset'] == 0xffffffff
                                        || $this->eocdr['CD entries total'] == 0xffff )
                                {
                                        $this->error( 'zip-unsupported', 'Central directory header indicates ZIP64, ' .
                                                'but we are in legacy mode. Rejecting this upload is necessary to avoid ' .
                                                'opening vulnerabilities on clients using OpenJDK 7 or later.' );
                                }

                                list( $offset, $size ) = $this->findOldCentralDirectory();
                                $this->readCentralDirectory( $offset, $size );
                        }
                } catch ( ZipDirectoryReaderError $e ) {
                        $status->fatal( $e->getErrorCode() );
                }

                fclose( $this->file );
                return $status;
        }

        /**
         * Throw an error, and log a debug message
         */
        function error( $code, $debugMessage ) {
                wfDebug( __CLASS__ . ": Fatal error: $debugMessage\n" );
                throw new ZipDirectoryReaderError( $code );
        }

        /**
         * Read the header which is at the end of the central directory,
         * unimaginatively called the "end of central directory record" by the ZIP
         * spec.
         */
        function readEndOfCentralDirectoryRecord() {
                $info = array(
                        'signature' => 4,
                        'disk' => 2,
                        'CD start disk' => 2,
                        'CD entries this disk' => 2,
                        'CD entries total' => 2,
                        'CD size' => 4,
                        'CD offset' => 4,
                        'file comment length' => 2,
                );
                $structSize = $this->getStructSize( $info );
                $startPos = $this->getFileLength() - 65536 - $structSize;
                if ( $startPos < 0 ) {
                        $startPos = 0;
                }

                $block = $this->getBlock( $startPos );
                $sigPos = strrpos( $block, "PK\x05\x06" );
                if ( $sigPos === false ) {
                        $this->error( 'zip-wrong-format',
                                "zip file lacks EOCDR signature. It probably isn't a zip file." );
                }

                $this->eocdr = $this->unpack( substr( $block, $sigPos ), $info );
                $this->eocdr['EOCDR size'] = $structSize + $this->eocdr['file comment length'];

                if ( $structSize + $this->eocdr['file comment length'] != strlen( $block ) - $sigPos ) {
                        $this->error( 'zip-bad', 'trailing bytes after the end of the file comment' );
                }
                if ( $this->eocdr['disk'] !== 0
                        || $this->eocdr['CD start disk'] !== 0 )
                {
                        $this->error( 'zip-unsupported', 'more than one disk (in EOCDR)' );
                }
                $this->eocdr += $this->unpack(
                        $block,
                        array( 'file comment' => array( 'string', $this->eocdr['file comment length'] ) ),
                        $sigPos + $structSize );
                $this->eocdr['position'] = $startPos + $sigPos;
        }

        /**
         * Read the header called the "ZIP64 end of central directory locator". An
         * error will be raised if it does not exist.
         */
        function readZip64EndOfCentralDirectoryLocator() {
                $info = array(
                        'signature' => array( 'string', 4 ),
                        'eocdr64 start disk' => 4,
                        'eocdr64 offset' => 8,
                        'number of disks' => 4,
                );
                $structSize = $this->getStructSize( $info );

                $block = $this->getBlock( $this->getFileLength() - $this->eocdr['EOCDR size']
                        - $structSize, $structSize );
                $this->eocdr64Locator = $data = $this->unpack( $block, $info );

                if ( $data['signature'] !== "PK\x06\x07" ) {
                        // Note: Java will allow this and continue to read the
                        // EOCDR64, so we have to reject the upload, we can't
                        // just use the EOCDR header instead.
                        $this->error( 'zip-bad', 'wrong signature on Zip64 end of central directory locator' );
                }
        }

        /**
         * Read the header called the "ZIP64 end of central directory record". It
         * may replace the regular "end of central directory record" in ZIP64 files.
         */
        function readZip64EndOfCentralDirectoryRecord() {
                if ( $this->eocdr64Locator['eocdr64 start disk'] != 0
                        || $this->eocdr64Locator['number of disks'] != 0 )
                {
                        $this->error( 'zip-unsupported', 'more than one disk (in EOCDR64 locator)' );
                }

                $info = array(
                        'signature' => array( 'string', 4 ),
                        'EOCDR64 size' => 8,
                        'version made by' => 2,
                        'version needed' => 2,
                        'disk' => 4,
                        'CD start disk' => 4,
                        'CD entries this disk' => 8,
                        'CD entries total' => 8,
                        'CD size' => 8,
                        'CD offset' => 8
                );
                $structSize = $this->getStructSize( $info );
                $block = $this->getBlock( $this->eocdr64Locator['eocdr64 offset'], $structSize );
                $this->eocdr64 = $data = $this->unpack( $block, $info );
                if ( $data['signature'] !== "PK\x06\x06" ) {
                        $this->error( 'zip-bad', 'wrong signature on Zip64 end of central directory record' );
                }
                if ( $data['disk'] !== 0
                        || $data['CD start disk'] !== 0 )
                {
                        $this->error( 'zip-unsupported', 'more than one disk (in EOCDR64)' );
                }
        }

        /**
         * Find the location of the central directory, as would be seen by a
         * non-ZIP64 reader.
         *
         * @return List containing offset, size and end position.
         */
        function findOldCentralDirectory() {
                $size = $this->eocdr['CD size'];
                $offset = $this->eocdr['CD offset'];
                $endPos = $this->eocdr['position'];

                // Some readers use the EOCDR position instead of the offset field
                // to find the directory, so to be safe, we check if they both agree.
                if ( $offset + $size != $endPos ) {
                        $this->error( 'zip-bad', 'the central directory does not immediately precede the end ' .
                                'of central directory record' );
                }
                return array( $offset, $size );
        }

        /**
         * Find the location of the central directory, as would be seen by a
         * ZIP64-compliant reader.
         *
         * @return array List containing offset, size and end position.
         */
        function findZip64CentralDirectory() {
                // The spec is ambiguous about the exact rules of precedence between the
                // ZIP64 headers and the original headers. Here we follow zip_util.c
                // from OpenJDK 7.
                $size = $this->eocdr['CD size'];
                $offset = $this->eocdr['CD offset'];
                $numEntries = $this->eocdr['CD entries total'];
                $endPos = $this->eocdr['position'];
                if ( $size == 0xffffffff
                        || $offset == 0xffffffff
                        || $numEntries == 0xffff )
                {
                        $this->readZip64EndOfCentralDirectoryLocator();

                        if ( isset( $this->eocdr64Locator['eocdr64 offset'] ) ) {
                                $this->readZip64EndOfCentralDirectoryRecord();
                                if ( isset( $this->eocdr64['CD offset'] ) ) {
                                        $size = $this->eocdr64['CD size'];
                                        $offset = $this->eocdr64['CD offset'];
                                        $endPos = $this->eocdr64Locator['eocdr64 offset'];
                                }
                        }
                }
                // Some readers use the EOCDR position instead of the offset field
                // to find the directory, so to be safe, we check if they both agree.
                if ( $offset + $size != $endPos ) {
                        $this->error( 'zip-bad', 'the central directory does not immediately precede the end ' .
                                'of central directory record' );
                }
                return array( $offset, $size );
        }

        /**
         * Read the central directory at the given location
         */
        function readCentralDirectory( $offset, $size ) {
                $block = $this->getBlock( $offset, $size );

                $fixedInfo = array(
                        'signature' => array( 'string', 4 ),
                        'version made by' => 2,
                        'version needed' => 2,
                        'general bits' => 2,
                        'compression method' => 2,
                        'mod time' => 2,
                        'mod date' => 2,
                        'crc-32' => 4,
                        'compressed size' => 4,
                        'uncompressed size' => 4,
                        'name length' => 2,
                        'extra field length' => 2,
                        'comment length' => 2,
                        'disk number start' => 2,
                        'internal attrs' => 2,
                        'external attrs' => 4,
                        'local header offset' => 4,
                );
                $fixedSize = $this->getStructSize( $fixedInfo );

                $pos = 0;
                while ( $pos < $size ) {
                        $data = $this->unpack( $block, $fixedInfo, $pos );
                        $pos += $fixedSize;

                        if ( $data['signature'] !== "PK\x01\x02" ) {
                                $this->error( 'zip-bad', 'Invalid signature found in directory entry' );
                        }

                        $variableInfo = array(
                                'name' => array( 'string', $data['name length'] ),
                                'extra field' => array( 'string', $data['extra field length'] ),
                                'comment' => array( 'string', $data['comment length'] ),
                        );
                        $data += $this->unpack( $block, $variableInfo, $pos );
                        $pos += $this->getStructSize( $variableInfo );

                        if ( $this->zip64 && (
                                   $data['compressed size'] == 0xffffffff
                                || $data['uncompressed size'] == 0xffffffff
                                || $data['local header offset'] == 0xffffffff ) )
                        {
                                $zip64Data = $this->unpackZip64Extra( $data['extra field'] );
                                if ( $zip64Data ) {
                                        $data = $zip64Data + $data;
                                }
                        }

                        if ( $this->testBit( $data['general bits'], self::GENERAL_CD_ENCRYPTED ) ) {
                                $this->error( 'zip-unsupported', 'central directory encryption is not supported' );
                        }

                        // Convert the timestamp into MediaWiki format
                        // For the format, please see the MS-DOS 2.0 Programmer's Reference,
                        // pages 3-5 and 3-6.
                        $time = $data['mod time'];
                        $date = $data['mod date'];

                        $year = 1980 + ( $date >> 9 );
                        $month = ( $date >> 5 ) & 15;
                        $day = $date & 31;
                        $hour = ( $time >> 11 ) & 31;
                        $minute = ( $time >> 5 ) & 63;
                        $second = ( $time & 31 ) * 2;
                        $timestamp = sprintf( "%04d%02d%02d%02d%02d%02d",
                                $year, $month, $day, $hour, $minute, $second );

                        // Convert the character set in the file name
                        if ( !function_exists( 'iconv' )
                                || $this->testBit( $data['general bits'], self::GENERAL_UTF8 ) )
                        {
                                $name = $data['name'];
                        } else {
                                $name = iconv( 'CP437', 'UTF-8', $data['name'] );
                        }

                        // Compile a data array for the user, with a sensible format
                        $userData = array(
                                'name' => $name,
                                'mtime' => $timestamp,
                                'size' => $data['uncompressed size'],
                        );
                        call_user_func( $this->callback, $userData );
                }
        }

        /**
         * Interpret ZIP64 "extra field" data and return an associative array.
         * @return array|bool
         */
        function unpackZip64Extra( $extraField ) {
                $extraHeaderInfo = array(
                        'id' => 2,
                        'size' => 2,
                );
                $extraHeaderSize = $this->getStructSize( $extraHeaderInfo );

                $zip64ExtraInfo = array(
                        'uncompressed size' => 8,
                        'compressed size' => 8,
                        'local header offset' => 8,
                        'disk number start' => 4,
                );

                $extraPos = 0;
                while ( $extraPos < strlen( $extraField ) ) {
                        $extra = $this->unpack( $extraField, $extraHeaderInfo, $extraPos );
                        $extraPos += $extraHeaderSize;
                        $extra += $this->unpack( $extraField,
                                array( 'data' => array( 'string', $extra['size'] ) ),
                                $extraPos );
                        $extraPos += $extra['size'];

                        if ( $extra['id'] == self::ZIP64_EXTRA_HEADER ) {
                                return $this->unpack( $extra['data'], $zip64ExtraInfo );
                        }
                }

                return false;
        }

        /**
         * Get the length of the file.
         */
        function getFileLength() {
                if ( $this->fileLength === null ) {
                        $stat = fstat( $this->file );
                        $this->fileLength = $stat['size'];
                }
                return $this->fileLength;
        }

        /**
         * Get the file contents from a given offset. If there are not enough bytes
         * in the file to satisfy the request, an exception will be thrown.
         *
         * @param int $start The byte offset of the start of the block.
         * @param int $length The number of bytes to return. If omitted, the remainder
         *    of the file will be returned.
         *
         * @return string
         */
        function getBlock( $start, $length = null ) {
                $fileLength = $this->getFileLength();
                if ( $start >= $fileLength ) {
                        $this->error( 'zip-bad', "getBlock() requested position $start, " .
                                "file length is $fileLength" );
                }
                if ( $length === null ) {
                        $length = $fileLength - $start;
                }
                $end = $start + $length;
                if ( $end > $fileLength ) {
                        $this->error( 'zip-bad', "getBlock() requested end position $end, " .
                                "file length is $fileLength" );
                }
                $startSeg = floor( $start / self::SEGSIZE );
                $endSeg = ceil( $end / self::SEGSIZE );

                $block = '';
                for ( $segIndex = $startSeg; $segIndex <= $endSeg; $segIndex++ ) {
                        $block .= $this->getSegment( $segIndex );
                }

                $block = substr( $block,
                        $start - $startSeg * self::SEGSIZE,
                        $length );

                if ( strlen( $block ) < $length ) {
                        $this->error( 'zip-bad', 'getBlock() returned an unexpectedly small amount of data' );
                }

                return $block;
        }

        /**
         * Get a section of the file starting at position $segIndex * self::SEGSIZE,
         * of length self::SEGSIZE. The result is cached. This is a helper function
         * for getBlock().
         *
         * If there are not enough bytes in the file to satisfy the request, the
         * return value will be truncated. If a request is made for a segment beyond
         * the end of the file, an empty string will be returned.
         * @return string
         */
        function getSegment( $segIndex ) {
                if ( !isset( $this->buffer[$segIndex] ) ) {
                        $bytePos = $segIndex * self::SEGSIZE;
                        if ( $bytePos >= $this->getFileLength() ) {
                                $this->buffer[$segIndex] = '';
                                return '';
                        }
                        if ( fseek( $this->file, $bytePos ) ) {
                                $this->error( 'zip-bad', "seek to $bytePos failed" );
                        }
                        $seg = fread( $this->file, self::SEGSIZE );
                        if ( $seg === false ) {
                                $this->error( 'zip-bad', "read from $bytePos failed" );
                        }
                        $this->buffer[$segIndex] = $seg;
                }
                return $this->buffer[$segIndex];
        }

        /**
         * Get the size of a structure in bytes. See unpack() for the format of $struct.
         * @return int
         */
        function getStructSize( $struct ) {
                $size = 0;
                foreach ( $struct as $type ) {
                        if ( is_array( $type ) ) {
                                list( , $fieldSize ) = $type;
                                $size += $fieldSize;
                        } else {
                                $size += $type;
                        }
                }
                return $size;
        }

        /**
         * Unpack a binary structure. This is like the built-in unpack() function
         * except nicer.
         *
         * @param string $string The binary data input
         *
         * @param array $struct An associative array giving structure members and their
         *    types. In the key is the field name. The value may be either an
         *    integer, in which case the field is a little-endian unsigned integer
         *    encoded in the given number of bytes, or an array, in which case the
         *    first element of the array is the type name, and the subsequent
         *    elements are type-dependent parameters. Only one such type is defined:
         *       - "string": The second array element gives the length of string.
         *          Not null terminated.
         *
         * @param int $offset The offset into the string at which to start unpacking.
         *
         * @throws MWException
         * @return array Unpacked associative array. Note that large integers in the input
         *    may be represented as floating point numbers in the return value, so
         *    the use of weak comparison is advised.
         */
        function unpack( $string, $struct, $offset = 0 ) {
                $size = $this->getStructSize( $struct );
                if ( $offset + $size > strlen( $string ) ) {
                        $this->error( 'zip-bad', 'unpack() would run past the end of the supplied string' );
                }

                $data = array();
                $pos = $offset;
                foreach ( $struct as $key => $type ) {
                        if ( is_array( $type ) ) {
                                list( $typeName, $fieldSize ) = $type;
                                switch ( $typeName ) {
                                case 'string':
                                        $data[$key] = substr( $string, $pos, $fieldSize );
                                        $pos += $fieldSize;
                                        break;
                                default:
                                        throw new MWException( __METHOD__ . ": invalid type \"$typeName\"" );
                                }
                        } else {
                                // Unsigned little-endian integer
                                $length = intval( $type );

                                // Calculate the value. Use an algorithm which automatically
                                // upgrades the value to floating point if necessary.
                                $value = 0;
                                for ( $i = $length - 1; $i >= 0; $i-- ) {
                                        $value *= 256;
                                        $value += ord( $string[$pos + $i] );
                                }

                                // Throw an exception if there was loss of precision
                                if ( $value > pow( 2, 52 ) ) {
                                        $this->error( 'zip-unsupported', 'number too large to be stored in a double. ' .
                                                'This could happen if we tried to unpack a 64-bit structure ' .
                                                'at an invalid location.' );
                                }
                                $data[$key] = $value;
                                $pos += $length;
                        }
                }

                return $data;
        }

        /**
         * Returns a bit from a given position in an integer value, converted to
         * boolean.
         *
         * @param $value integer
         * @param int $bitIndex The index of the bit, where 0 is the LSB.
         * @return bool
         */
        function testBit( $value, $bitIndex ) {
                return (bool)( ( $value >> $bitIndex ) & 1 );
        }

        /**
         * Debugging helper function which dumps a string in hexdump -C format.
         */
        function hexDump( $s ) {
                $n = strlen( $s );
                for ( $i = 0; $i < $n; $i += 16 ) {
                        printf( "%08X ", $i );
                        for ( $j = 0; $j < 16; $j++ ) {
                                print " ";
                                if ( $j == 8 ) {
                                        print " ";
                                }
                                if ( $i + $j >= $n ) {
                                        print "  ";
                                } else {
                                        printf( "%02X", ord( $s[$i + $j] ) );
                                }
                        }

                        print "  |";
                        for ( $j = 0; $j < 16; $j++ ) {
                                if ( $i + $j >= $n ) {
                                        print " ";
                                } elseif ( ctype_print( $s[$i + $j] ) ) {
                                        print $s[$i + $j];
                                } else {
                                        print '.';
                                }
                        }
                        print "|\n";
                }
        }
}

/**
 * Internal exception class. Will be caught by private code.
 */
class ZipDirectoryReaderError extends Exception {
        var $errorCode;

        function __construct( $code ) {
                $this->errorCode = $code;
                parent::__construct( "ZipDirectoryReader error: $code" );
        }

        /**
         * @return mixed
         */
        function getErrorCode() {
                return $this->errorCode;
        }
}