Set frame-ancestors to none if none are filled

frame-ancestors doesn't fall back to default-src. So when we apply a
very restricted CSP we should make sure to set it to 'none' and not
leave it empty.

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

build/integration/sharing_features/sharing-v1.feature

@@ -14,7 +14,7 @@ Feature: sharing
     Then the OCS status code should be "100"
     And the HTTP status code should be "200"
     And The following headers should be set
-      | Content-Security-Policy | default-src 'none';base-uri 'none';manifest-src 'self' |
+      | Content-Security-Policy | default-src 'none';base-uri 'none';manifest-src 'self';frame-ancestors 'none' |
 
   Scenario: Creating a share with a group
     Given user "user0" exists

lib/public/AppFramework/Http/EmptyContentSecurityPolicy.php

@@ -509,6 +509,8 @@ public function buildPolicy() {
 		if (!empty($this->allowedFrameAncestors)) {
 			$policy .= 'frame-ancestors ' . implode(' ', $this->allowedFrameAncestors);
 			$policy .= ';';
+		} else {
+			$policy .= 'frame-ancestors \'none\';';
 		}
 
 		if (!empty($this->allowedWorkerSrcDomains)) {

tests/lib/AppFramework/Controller/ControllerTest.php

@@ -112,7 +112,7 @@ public function testFormatDataResponseJSON() {
 			'test' => 'something',
 			'Cache-Control' => 'no-cache, no-store, must-revalidate',
 			'Content-Type' => 'application/json; charset=utf-8',
-			'Content-Security-Policy' => "default-src 'none';base-uri 'none';manifest-src 'self'",
+			'Content-Security-Policy' => "default-src 'none';base-uri 'none';manifest-src 'self';frame-ancestors 'none'",
 			'Feature-Policy' => "autoplay 'none';camera 'none';fullscreen 'none';geolocation 'none';microphone 'none';payment 'none'",
 			'X-Robots-Tag' => 'none',
 		];

tests/lib/AppFramework/Http/DataResponseTest.php

@@ -65,7 +65,7 @@ public function testConstructorAllowsToSetHeaders() {
 
 		$expectedHeaders = [
 			'Cache-Control' => 'no-cache, no-store, must-revalidate',
-			'Content-Security-Policy' => "default-src 'none';base-uri 'none';manifest-src 'self'",
+			'Content-Security-Policy' => "default-src 'none';base-uri 'none';manifest-src 'self';frame-ancestors 'none'",
 			'Feature-Policy' => "autoplay 'none';camera 'none';fullscreen 'none';geolocation 'none';microphone 'none';payment 'none'",
 			'X-Robots-Tag' => 'none',
 		];