[BUG] Flawed UI Settings handling causes 500 error

[AMoo-Miki]

Describe the bug

OSD fetches the config:<version> from the metadata store and uses the output without proper if it is correctly formatted. This can result in unhelpful 500 errors.

SavedObjectsRepository.get makes the call to get the metadata attributes; here type = 'config'

OpenSearch-Dashboards/src/core/server/saved_objects/service/lib/repository.ts

Lines 988 to 998 in fe1f1d1

	return {
	id,
	type,
	namespaces,
	...(originId && { originId }),
	...(updatedAt && { updated_at: updatedAt }),
	version: encodeHitVersion(body),
	attributes: body._source[type],
	references: body._source.references || [],
	migrationVersion: body._source.migrationVersion,
	};

The output can contain attributes: undefined when _source = {}. The attributes are indiscriminately passed on:

OpenSearch-Dashboards/src/core/server/ui_settings/ui_settings_client.ts

Lines 234 to 235 in fe1f1d1

	const resp = await this.savedObjectsClient.get<Record<string, any>>(this.type, this.id);
	return this.translateChanges(resp.attributes, 'timelion', 'timeline');

And are used without any care in

OpenSearch-Dashboards/src/core/server/ui_settings/ui_settings_client.ts

Lines 280 to 285 in fe1f1d1

	private translateChanges(changes: Record<string, any>, source: string, dest: string) {
	return Object.keys(changes).reduce((translatedChanges: Record<string, any>, key: string) => {
	translatedChanges[key.replace(source, dest)] = changes[key];
	return translatedChanges;
	}, {});
	}

This results in a TypeError which caught and re-thrown.

Expected behavior
A beautiful notification telling me that my configuration is corrupted because _source is expected to have something in it. Or, at least don't show a 500 error. The code should not attempt to create it because _source being empty could be due to Field Level Security.

[kavilla]

@AMoo-Miki can another issue/campaign be implemented to avoid this common re-occurrence that plugins gives end users the ability to directly impact system indices without them knowing about it?

Within core OpenSearch Dashboards, the default behavior is to hide system indices so the user can have no clue that requests related to indices and pass wildcard can hit system indices. Nor do I think they usually want to. For this, I wouldn't see the benefit in FLS on non-data indices. Or applying a index mapping template to system indices (modifying .kibana).