GIF metadata extraction fixes:

* Fast failure when inconsistencies are detected.
* Skip non-GCF, non-application extensions too.
* Fix error where seeking was not being done properly for non-netscape application extensions.

diff --git a/includes/media/GIFMetadataExtractor.php b/includes/media/GIFMetadataExtractor.php
index 1b6589b..0e9c62b 100644 (file)
--- a/includes/media/GIFMetadataExtractor.php
+++ b/includes/media/GIFMetadataExtractor.php
@@ -57,7 +57,7 @@ class GIFMetadataExtractor {
                                // Found a frame
                                $frameCount++;
                                
-                               ## Skip dimensions (Why is this 8 bytes and not 4?)
+                               ## Skip bounding box
                                fread( $fh, 8 );
                                
                                ## Read BPP
@@ -76,6 +76,7 @@ class GIFMetadataExtractor {
                                if ($extension_code == 0xF9) {
                                        // Graphics Control Extension.
                                        fread( $fh, 1 ); // Block size
+                                       
                                        fread( $fh, 1 ); // Transparency, disposal method, user input
                                        
                                        $buf = fread( $fh, 2 ); // Delay, in hundredths of seconds.
@@ -99,11 +100,16 @@ class GIFMetadataExtractor {
                                        
                                        // NETSCAPE2.0 (application name)
                                        if ($blockLength != 11 || $data != 'NETSCAPE2.0') {
+                                               fseek( $fh, -($blockLength + 1), SEEK_CUR );
                                                self::skipBlock();
                                                continue;
                                        }
                                        
-                                       fread( $fh, 2 ); // Block length and introduction, should be 03 01
+                                       $data = fread( $fh, 2 ); // Block length and introduction, should be 03 01
+                                       
+                                       if ($data != "\x03\x01") {
+                                               throw new Exception( "Expected \x03\x01, got $data" );
+                                       }
                                        
                                        // Unsigned little-endian integer, loop count or zero for "forever"
                                        $loopData = fread( $fh, 2 );
@@ -116,6 +122,8 @@ class GIFMetadataExtractor {
                                        
                                        // Read out terminator byte
                                        fread( $fh, 1 );
+                               } else {
+                                       self::skipBlock( $fh );
                                }
                        } elseif ( $buf == self::$gif_term ) {
                                break;
@@ -164,4 +172,4 @@ class GIFMetadataExtractor {
                }
        }
 
-}
\ No newline at end of file
+}