Server: getPreview on a broken image shouldn't crash

[leo-b]

When trying to obtain a preview from a broken image file, nextcloud 12 currently crashes:

An unhandled exception has been thrown:
Error: Call to a member function file_get_contents() on null in /usr/local/nextcloud/nextcloud-12.0.2/lib/private/Files/Filesystem.php:717
Stack trace:
#0 /usr/local/nextcloud/nextcloud-12.0.2/lib/private/legacy/image.php(628): OC\Files\Filesystem::file_get_contents('/srv/nextcloud/...')
#1 /usr/local/nextcloud/nextcloud-12.0.2/lib/private/Preview/Image.php(57): OC_Image->loadFromFile('/srv/nextcloud/...')
#2 /usr/local/nextcloud/nextcloud-12.0.2/lib/private/Preview/GeneratorHelper.php(54): OC\Preview\Image->getThumbnail('/files/MALE/alb...', 2048, 2048, false, Object(OC\Files\View))
#3 /usr/local/nextcloud/nextcloud-12.0.2/lib/private/Preview/Generator.php(162): OC\Preview\GeneratorHelper->getThumbnail(Object(OC\Preview\JPEG), Object(OC\Files\Node\File), 2048, 2048)
#4 /usr/local/nextcloud/nextcloud-12.0.2/lib/private/Preview/Generator.php(110): OC\Preview\Generator->getMaxPreview(Object(OC\Files\SimpleFS\SimpleFolder), Object(OC\Files\Node\File), 'image/jpeg')
#5 /usr/local/nextcloud/nextcloud-12.0.2/lib/private/PreviewManager.php(201): OC\Preview\Generator->getPreview(Object(OC\Files\Node\File), 32, 32, true, 'fill', 'image/jpeg')
#6 /usr/local/nextcloud/nextcloud-12.0.2/apps/previewgenerator/lib/Command/PreGenerate.php(213): OC\PreviewManager->getPreview(Object(OC\Files\Node\File), 32, 32, true)
#7 /usr/local/nextcloud/nextcloud-12.0.2/apps/previewgenerator/lib/Command/PreGenerate.php(245): OCA\PreviewGenerator\Command\PreGenerate->processFile(Object(OC\Files\Node\File))
#8 /usr/local/nextcloud/nextcloud-12.0.2/apps/previewgenerator/lib/Command/PreGenerate.php(247): OCA\PreviewGenerator\Command\PreGenerate->processFolder(Object(OC\Files\Node\Folder))
#9 /usr/local/nextcloud/nextcloud-12.0.2/apps/previewgenerator/lib/Command/PreGenerate.php(247): OCA\PreviewGenerator\Command\PreGenerate->processFolder(Object(OC\Files\Node\Folder))
#10 /usr/local/nextcloud/nextcloud-12.0.2/apps/previewgenerator/lib/Command/PreGenerate.php(247): OCA\PreviewGenerator\Command\PreGenerate->processFolder(Object(OC\Files\Node\Folder))
#11 /usr/local/nextcloud/nextcloud-12.0.2/apps/previewgenerator/lib/Command/PreGenerate.php(201): OCA\PreviewGenerator\Command\PreGenerate->processFolder(Object(OC\Files\Node\Folder))
#12 /usr/local/nextcloud/nextcloud-12.0.2/apps/previewgenerator/lib/Command/PreGenerate.php(170): OCA\PreviewGenerator\Command\PreGenerate->processRow(Array)
#13 /usr/local/nextcloud/nextcloud-12.0.2/apps/previewgenerator/lib/Command/PreGenerate.php(137): OCA\PreviewGenerator\Command\PreGenerate->startProcessing()
#14 /usr/local/nextcloud/nextcloud-12.0.2/3rdparty/symfony/console/Command/Command.php(256): OCA\PreviewGenerator\Command\PreGenerate->execute(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#15 /usr/local/nextcloud/nextcloud-12.0.2/3rdparty/symfony/console/Application.php(818): Symfony\Component\Console\Command\Command->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#16 /usr/local/nextcloud/nextcloud-12.0.2/3rdparty/symfony/console/Application.php(186): Symfony\Component\Console\Application->doRunCommand(Object(OCA\PreviewGenerator\Command\PreGenerate), Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#17 /usr/local/nextcloud/nextcloud-12.0.2/3rdparty/symfony/console/Application.php(117): Symfony\Component\Console\Application->doRun(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#18 /usr/local/nextcloud/nextcloud-12.0.2/lib/private/Console/Application.php(170): Symfony\Component\Console\Application->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#19 /usr/local/nextcloud/nextcloud-12.0.2/console.php(100): OC\Console\Application->run()
#20 /usr/local/nextcloud/nextcloud-12.0.2/occ(11): require_once('/usr/local/next...')
#21 {main}

(Tested with a _.jpg_ file containing only null characters. Preview generation was triggered by the preview generator app.)

exif_imagetype($imagePath) fails determining the image type. The following file-type switch statement falls back to the default case and fails because Filesystem isn't configured:

            default:

                // this is mostly file created from encrypted file
                $this->resource = imagecreatefromstring(\OC\Files\Filesystem::file_get_contents(\OC\Files\Filesystem::getLocalPath($imagePath)));
                $iType = IMAGETYPE_PNG;
                $this->logger->debug('OC_Image->loadFromFile, Default', array('app' => 'core'));
                break;

My workaround for this is:

            default:

                // this is mostly file created from encrypted file
                if (\OC\Files\Filesystem::getView() === null) {
                    $this->logger->warning('LEO: Bad image: '.$imagePath);
                    $this->resource = file_get_contents($imagePath);
                    // return false;
                } else {
                    $this->resource = imagecreatefromstring(\OC\Files\Filesystem::file_get_contents(\OC\Files\Filesystem::getLocalPath($imagePath)));
                }
                $iType = IMAGETYPE_PNG;
                $this->logger->debug('OC_Image->loadFromFile, Default', array('app' => 'core'));
                break;

... which certainly isn't the optimal solution. (I don't know if the file contents are useful at all in this case.) But at least it doesn't crash.

[MorrisJobke]

cc @rullzer

[blizzz]

Is this still a thing?

[rullzer]

yeah it is.
I guess we can do better now with php7.

But I would need a broken jpg to test with

[matiasdelellis]

Hi @rullzer

The bug is still present. Come here for this report. https://github.com/matiasdelellis/facerecognition/issues/295

But I would need a broken jpg to test with.

MMM.. The main problem is that Nexcloud trusts the extensions very much. if the file has .jpg extension, already returns mimetype 'image/jpeg'. I trust in this mimetype, and try to open it with OC_Image. and for example the file is an mp4 video, with jpeg extension (This is the case that started our bug report.), fails miserably as this report. :sweat:

So, here an example: https://delellis.com.ar/s/x7yw66odGqPCKwF

It is just an mp4 with jpg extension..

[cliffalbert]

I am experiencing the same issues. For example if a file with a .jpg extension is actually a html file it will generate this same problem.

[strugee]

You don't need an MP4 file or a corrupted picture to trigger this. Just create an empty file and stick .jpg onto the end of the filename. I've got a bunch of empty .jpg files lying around (legacy of a filesystem crash without proper backups...) and they consistently trigger this bug in the Face Recognition app.