Fix "The operation is insecure" when accessing cssRules

In Firefox accessing "cssRules" may throw a "SecurityError" if the style
sheet was loaded from a different domain. The style sheets loaded by
Nextcloud all come from the same domain, but some Firefox extensions
inject their own stylesheets from a different domain. Due to this, when
the style sheet from the vue-at component was being looked for those
style sheets from a different domain could be iterated over, which
caused the exception to be thrown and stopped the load of Talk, which
ended causing a blank page.

In a similar way this caused an exception to be thrown when starting a
call in the Files app sidebar, which ended causing the call view to not
be shown in the sidebar.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>

1 files changed, 35 insertions, 14 deletions

diff --git a/src/FilesSidebarCallViewApp.vue b/src/FilesSidebarCallViewApp.vue
index ad5b9d98c..c7226244d 100644
--- a/src/FilesSidebarCallViewApp.vue
+++ b/src/FilesSidebarCallViewApp.vue
@@ -161,23 +161,44 @@ export default {
 		 * call.
 		 */
 		addCallInFilesSidebarStyleSheet() {
-			for (let i = 0; i < document.styleSheets.length; i++) {
-				const sheet = document.styleSheets[i]
-				// None of the default properties of a style sheet can be used
-				// as an ID. Adding a "data-id" attribute would work in Firefox,
-				// but not in Chromium, as it does not provide a "dataset"
-				// property in styleSheet objects. Therefore it is necessary to
-				// check the rules themselves, but as the order is undefined a
-				// matching rule needs to be looked for in all of them.
-				if (sheet.cssRules.length !== 2) {
-					continue
-				}
+			const isCallInFilesSidebarStyleSheet = (sheet) => {
+				try {
+					// cssRules may not be defined in Chromium if the stylesheet
+					// is loaded from a different domain.
+					if (!sheet.cssRules) {
+						return false
+					}
 
-				for (const cssRule of sheet.cssRules) {
-					if (cssRule.cssText === '.app-sidebar-header .hidden-by-call { display: none !important; }') {
-						return
+					// None of the default properties of a style sheet can be used
+					// as an ID. Adding a "data-id" attribute would work in Firefox,
+					// but not in Chromium, as it does not provide a "dataset"
+					// property in styleSheet objects. Therefore it is necessary to
+					// check the rules themselves, but as the order is undefined a
+					// matching rule needs to be looked for in all of them.
+					if (sheet.cssRules.length !== 2) {
+						return false
+					}
+
+					for (const cssRule of sheet.cssRules) {
+						if (cssRule.cssText === '.app-sidebar-header .hidden-by-call { display: none !important; }') {
+							return true
+						}
+					}
+				} catch (exception) {
+					// Accessing cssRules may throw a SecurityError in Firefox
+					// if the style sheet is loaded from a different domain.
+					if (exception.name !== 'SecurityError') {
+						throw exception
 					}
 				}
+
+				return false
+			}
+
+			for (let i = 0; i < document.styleSheets.length; i++) {
+				if (isCallInFilesSidebarStyleSheet(document.styleSheets[i])) {
+					return
+				}
 			}
 
 			const style = document.createElement('style')