https://bugzilla.wikimedia.org/show_bug.cgi?id=20364
Summary: GIFMetadataExtractor.php throws "Unexpected non-
MediaWiki exception encountered, of type 'Exception'",
halts if metadata in user-provided image not accepted
Product: MediaWiki
Version: 1.16-svn
Platform: PC
URL: http://jpe.gs/wiki/File:Sucrose_b.gif
OS/Version: Linux
Status: NEW
Severity: normal
Priority: Normal
Component: Images and files
AssignedTo: [email protected]
ReportedBy: [email protected]
The error handling in GIFMetadataExtractor.php appears to create more problems
than it solves. If the script finds the smallest bit of the metadata
objectionable in a user-supplied image, it does not allow any part of the page
on which the image appears to display.
Errors which could be safely ignored (for instance, the
http://jpe.gs/wiki/File:Sucrose_b.gif file triggering an error at
GIFMetadataExtractor.php:133) instead now prevent the display of the entire
page, for every page in every wiki on which the image appears.
This issue appeared on 'upgrade' from MediaWiki 1.14 to the August 15, 2009 SVN
version 1.16alpha - header in the metadata extractor file claims to be avoiding
use of the MWException class for portability reasons, but even no displayed
metadata at all would be better than entire wiki pages turned into:
Unexpected non-MediaWiki exception encountered, of type "Exception"
exception 'Exception' with message 'At position: 208, Unknown byte 11' in
...mw116a/includes/media/GIFMetadataExtractor.php:133
Stack trace:
#0 ...mw116a/includes/media/GIF.php(16):
GIFMetadataExtractor::getMetadata('/var/im...')
#1 ...mw116a/includes/filerepo/UnregisteredLocalFile.php(89):
GIFHandler->getMetadata(Object(UnregisteredLocalFile), '/var/im...')
#2 ...mw116a/includes/filerepo/File.php(899):
UnregisteredLocalFile->getMetadata()
#3 ...mw116a/includes/ImagePage.php(90): File->formatMetadata()
#4 ...mw116a/includes/Wiki.php(463): ImagePage->view()
#5 ...mw116a/includes/Wiki.php(67):
MediaWiki->performAction(Object(OutputPage), Object(ImagePage), Object(Title),
Object(User), Object(WebRequest))
#6 ...mw116a/index.php(116): MediaWiki->performRequestForTitle(Object(Title),
Object(ImagePage), Object(OutputPage), Object(User), Object(WebRequest))
#7 {main}
#0 ...mw116a/includes/media/GIF.php(16):
GIFMetadataExtractor::getMetadata('/var/im...')
#1 ...mw116a/includes/filerepo/UnregisteredLocalFile.php(89):
GIFHandler->getMetadata(Object(UnregisteredLocalFile), '/var/im...')
#2 ...mw116a/includes/filerepo/File.php(899):
UnregisteredLocalFile->getMetadata()
#3 ...mw116a/includes/ImagePage.php(90): File->formatMetadata()
#4 ...mw116a/includes/Wiki.php(463): ImagePage->view()
#5 ...mw116a/includes/Wiki.php(67):
MediaWiki->performAction(Object(OutputPage), Object(ImagePage), Object(Title),
Object(User), Object(WebRequest))
#6 ...mw116a/index.php(116): MediaWiki->performRequestForTitle(Object(Title),
Object(ImagePage), Object(OutputPage), Object(User), Object(WebRequest))
#7 {main}
Disabling the one "throw new Exception" line of code throwing the error
(includes/media/GIFMetadataExtractor.php:133) allows the image to display
normally:
} else {
$byte = unpack( 'C', $buf );
$byte = $byte[1];
#throw new Exception( "At position:
".ftell($fh). ", Unknown byte ".$byte );
}
Oddly, the image itself looks fine in the browser. Whatever supposed 'error'
exists in this animated .gif file is not valid enough that is should be used to
justify MediaWiki 1.16a refusing to display the entire page, for every page
where the image appears.
Any chance the code could be changed to recover just a wee bit more gracefully?
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