fix(entity): prevent deadloops during recursive entity delete

fixes #10836

engine/classes/Elgg/Database/EntityTable.php

@@ -82,6 +82,11 @@ class EntityTable {
 	 * @var Translator
 	 */
 	protected $translator;
+
+	/**
+	 * @var int[]
+	 */
+	protected $deleted_guids = [];
 
 	/**
 	 * Constructor
@@ -561,6 +566,9 @@ public function delete(\ElggEntity $entity, $recursive = true) {
 			$entity->ban();
 		}
 
+		// we're going to delete this entity, log the guid to prevent deadloops
+		$this->deleted_guids[] = $entity->guid;
+
 		if ($recursive) {
 			$this->deleteRelatedEntities($entity);
 		}
@@ -606,6 +614,12 @@ protected function deleteRelatedEntities(\ElggEntity $entity) {
 			]);
 			/* @var $e \ElggEntity */
 			foreach ($batch as $e) {
+				if (in_array($e->guid, $this->deleted_guids)) {
+					// prevent deadloops, doing this here in case of large deletes which could cause query length issues
+					$batch->reportFailure();
+					continue;
+				}
+
 				if (!$this->delete($e, true)) {
 					$batch->reportFailure();
 				}

engine/tests/phpunit/integration/Elgg/Integration/ElggCoreEntityTest.php

@@ -696,4 +696,38 @@ public function emptyValues() {
 		];
 	}
 
+	public function testDeleteDeadloopPrevented() {
+		$user = $this->getAdmin();
+
+		$session = elgg_get_session();
+		$session->setLoggedInUser($user);
+
+		$object1 = $this->createObject([
+			'owner_guid' => $user->guid,
+		]);
+		$object2 = $this->createObject([
+			'owner_guid' => $user->guid,
+			'container_guid' => $object1->guid,
+		]);
+		$object3 = $this->createObject([
+			'owner_guid' => $user->guid,
+			'container_guid' => $object2->guid,
+		]);
+
+		$object1->container_guid = $object3->guid;
+		$object1->save();
+
+		$called_guids = [];
+		$testing_event = $this->registerTestingEvent('delete:before', 'object', function(\Elgg\Event $event) use (&$called_guids) {
+			$object = $event->getObject();
+			$this->assertNotContains($object->guid, $called_guids, 'Deadloop detected during entity delete');
+
+			$called_guids[] = $object->guid;
+		});
+
+		$object1->delete();
+
+		$testing_event->assertNumberOfCalls(3);
+		$testing_event->unregister();
+	}
 }