Properly catch whether a share is `null`

Despite it's PHPDoc the function might return `null` which was not properly catched and thus in some situations the share was resolved to the sharing users root directory.

To test this perform the following steps:

* Share file in owncloud 7 (7.0.4.2)
* Delete the parent folder of the shared file
* The share stays is in the DB and the share via the sharelink is inaccessible. (which is good)
* Upgrade to owncloud 8 (8.0.2) (This step is crucial. The bug is not reproduceable without upgrading from 7 to 8. It seems like the old tokens are handled different than the newer ones)
* Optional Step: Logout, Reset Browser Session, etc.
* Access the share via the old share url: almost empty page, but there is a dowload button which adds a "/download" to the URL.
* Upon clicking, a download.zip is downloaded which contains EVERYTHING from the owncloud directory (of the user who shared the file)
* No exception is thrown and no error is logged.

This will add a check whether the share is a valid one and also adds unit tests to prevent further regressions in the future. Needs to be backported to ownCloud 8.

Adding a proper clean-up of the orphaned shares is out-of-scope and would probably require some kind of FK or so.

Fixes https://github.com/owncloud/core/issues/15097

1 files changed, 2 insertions, 1 deletions

diff --git a/apps/files_sharing/lib/middleware/sharingcheckmiddleware.php b/apps/files_sharing/lib/middleware/sharingcheckmiddleware.php
index 3508407f2a0..3e7cdf4aa34 100644
--- a/apps/files_sharing/lib/middleware/sharingcheckmiddleware.php
+++ b/apps/files_sharing/lib/middleware/sharingcheckmiddleware.php
@@ -11,6 +11,7 @@
 namespace OCA\Files_Sharing\Middleware;
 
 use OCP\App\IAppManager;
+use OCP\AppFramework\Http\NotFoundResponse;
 use OCP\AppFramework\Middleware;
 use OCP\AppFramework\Http\TemplateResponse;
 use OCP\IConfig;
@@ -59,7 +60,7 @@ class SharingCheckMiddleware extends Middleware {
 	 * @return TemplateResponse
 	 */
 	public function afterException($controller, $methodName, \Exception $exception){
-		return new TemplateResponse('core', '404', array(), 'guest');
+		return new NotFoundResponse();
 	}
 
 	/**