fix(preview): check mime type before processing with Imagick

Signed-off-by: Varun Patil <varunpatil@ucla.edu>

Author: pulsejet

lib/private/Preview/Bitmap.php

@@ -37,6 +37,15 @@
  * @package OC\Preview
  */
 abstract class Bitmap extends ProviderV2 {
+	/**
+	 * List of MIME types that this preview provider is allowed to process.
+	 *
+	 * @return string Regular expression
+	 */
+	public function getAllowedMimeTypes(): string {
+		return '/.*/';
+	}
+
 	/**
 	 * {@inheritDoc}
 	 */
@@ -90,6 +99,13 @@ public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
 	private function getResizedPreview($tmpPath, $maxX, $maxY) {
 		$bp = new Imagick();
 
+		// Validate mime type
+		$bp->pingImage($tmpPath . '[0]');
+		$mimeType = $bp->getImageMimeType();
+		if (!preg_match($this->getAllowedMimeTypes(), $mimeType)) {
+			throw new \Exception('File mime type does not match the preview provider: ' . $mimeType);
+		}
+
 		// Layer 0 contains either the bitmap or a flat representation of all vector layers
 		$bp->readImage($tmpPath . '[0]');
 

lib/private/Preview/Font.php

@@ -30,4 +30,11 @@ class Font extends Bitmap {
 	public function getMimeType(): string {
 		return '/application\/(?:font-sfnt|x-font$)/';
 	}
+
+	/**
+	 * {@inheritDoc}
+	 */
+	public function getAllowedMimeTypes(): string {
+		return '/(application|image)\/(?:font-sfnt|x-font|x-otf|x-ttf|x-pfb$)/';
+	}
 }

lib/private/Preview/HEIC.php

@@ -44,7 +44,7 @@ class HEIC extends ProviderV2 {
 	 * {@inheritDoc}
 	 */
 	public function getMimeType(): string {
-		return '/image\/hei(f|c)/';
+		return '/image\/(x-)?hei(f|c)/';
 	}
 
 	/**
@@ -112,6 +112,14 @@ public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
 	private function getResizedPreview($tmpPath, $maxX, $maxY) {
 		$bp = new \Imagick();
 
+		// Some HEIC files just contain (or at least are identified as) other formats
+		// like JPEG. We just need to check if the image is safe to process.
+		$bp->pingImage($tmpPath . '[0]');
+		$mimeType = $bp->getImageMimeType();
+		if (!preg_match('/^image\/(x-)?(png|jpeg|gif|bmp|tiff|webp|hei(f|c)|avif)$/', $mimeType)) {
+			throw new \Exception('File mime type does not match the preview provider: ' . $mimeType);
+		}
+
 		// Layer 0 contains either the bitmap or a flat representation of all vector layers
 		$bp->readImage($tmpPath . '[0]');
 

lib/private/Preview/IMagickSupport.php

@@ -37,4 +37,8 @@ public function supportsFormat(string $format): bool {
 		$this->cache->set($format, $cached);
 		return $formatSupported;
 	}
+
+	public static function isSafeMimeType(string $mimeType): bool {
+		return preg_match('/^image\/(png|jpeg|gif|bmp|tiff|webp|hei(f|c))$/', $mimeType) > 0;
+	}
 }

lib/private/Preview/Illustrator.php

@@ -31,4 +31,11 @@ class Illustrator extends Bitmap {
 	public function getMimeType(): string {
 		return '/application\/illustrator/';
 	}
+
+	/**
+	 * {@inheritDoc}
+	 */
+	public function getAllowedMimeTypes(): string {
+		return '/application\/(illustrator|pdf)/';
+	}
 }

lib/private/Preview/PDF.php

@@ -31,4 +31,11 @@ class PDF extends Bitmap {
 	public function getMimeType(): string {
 		return '/application\/pdf/';
 	}
+
+	/**
+	 * {@inheritDoc}
+	 */
+	public function getAllowedMimeTypes(): string {
+		return '/application\/pdf/';
+	}
 }

lib/private/Preview/Photoshop.php

@@ -31,4 +31,11 @@ class Photoshop extends Bitmap {
 	public function getMimeType(): string {
 		return '/application\/x-photoshop/';
 	}
+
+	/**
+	 * {@inheritDoc}
+	 */
+	public function getAllowedMimeTypes(): string {
+		return '/(application|image)\/(x-photoshop|x-psd)/';
+	}
 }

lib/private/Preview/Postscript.php

@@ -31,4 +31,11 @@ class Postscript extends Bitmap {
 	public function getMimeType(): string {
 		return '/application\/postscript/';
 	}
+
+	/**
+	 * {@inheritDoc}
+	 */
+	public function getAllowedMimeTypes(): string {
+		return '/application\/postscript/';
+	}
 }

lib/private/Preview/SGI.php

@@ -28,6 +28,13 @@ class SGI extends Bitmap {
 	 * {@inheritDoc}
 	 */
 	public function getMimeType(): string {
-		return '/image\/sgi/';
+		return '/image\/(x-)?sgi/';
+	}
+
+	/**
+	 * {@inheritDoc}
+	 */
+	public function getAllowedMimeTypes(): string {
+		return '/image\/(x-)?sgi/';
 	}
 }

lib/private/Preview/SVG.php

@@ -44,9 +44,6 @@ public function getMimeType(): string {
 	 */
 	public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
 		try {
-			$svg = new \Imagick();
-			$svg->setBackgroundColor(new \ImagickPixel('transparent'));
-
 			$content = stream_get_contents($file->fopen('r'));
 			if (substr($content, 0, 5) !== '<?xml') {
 				$content = '<?xml version="1.0" encoding="UTF-8" standalone="no"?>' . $content;
@@ -57,13 +54,25 @@ public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
 				return null;
 			}
 
+			$svg = new \Imagick();
+
+			$svg->pingImageBlob($content);
+			$mimeType = $svg->getImageMimeType();
+			if (!preg_match($this->getMimeType(), $mimeType)) {
+				throw new \Exception('File mime type does not match the preview provider: ' . $mimeType);
+			}
+
+			$svg->setBackgroundColor(new \ImagickPixel('transparent'));
 			$svg->readImageBlob($content);
 			$svg->setImageFormat('png32');
 		} catch (\Exception $e) {
-			\OC::$server->get(LoggerInterface::class)->error($e->getMessage(), [
-				'exception' => $e,
-				'app' => 'core',
-			]);
+			\OC::$server->get(LoggerInterface::class)->error(
+				'File: ' . $file->getPath() . ' Imagick says:',
+				[
+					'exception' => $e,
+					'app' => 'core',
+				]
+			);
 			return null;
 		}