From 4653394a1fbd29cf50a77202fac539a6984c9aaf Mon Sep 17 00:00:00 2001
From: Travis Ralston <travisr@matrix.org>
Date: Thu, 16 Jun 2022 23:15:02 -0600
Subject: [PATCH] Guard watchers against invalid settings (#8857)

---
 src/settings/SettingsStore.ts | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/src/settings/SettingsStore.ts b/src/settings/SettingsStore.ts
index b0d2bb75f32..c1c488bf9ec 100644
--- a/src/settings/SettingsStore.ts
+++ b/src/settings/SettingsStore.ts
@@ -174,6 +174,14 @@ export default class SettingsStore {
         const watcherId = `${new Date().getTime()}_${SettingsStore.watcherCount++}_${settingName}_${roomId}`;
 
         const localizedCallback = (changedInRoomId: string | null, atLevel: SettingLevel, newValAtLevel: any) => {
+            if (!SettingsStore.doesSettingSupportLevel(originalSettingName, atLevel)) {
+                logger.warn(
+                    `Setting handler notified for an update of an invalid setting level: ` +
+                    `${originalSettingName}@${atLevel} - this likely means a weird setting value ` +
+                    `made it into the level's storage. The notification will be ignored.`,
+                );
+                return;
+            }
             const newValue = SettingsStore.getValue(originalSettingName);
             const newValueAtLevel = SettingsStore.getValueAt(atLevel, originalSettingName) ?? newValAtLevel;
             callbackFn(originalSettingName, changedInRoomId, atLevel, newValueAtLevel, newValue);
@@ -516,6 +524,23 @@ export default class SettingsStore {
         return LEVEL_HANDLERS[level].isSupported();
     }
 
+    /**
+     * Determines if a setting supports a particular level.
+     * @param settingName The setting name.
+     * @param level The level.
+     * @returns True if supported, false otherwise. Note that this will not check to see if
+     * the level itself can be supported by the runtime (ie: you will need to call #isLevelSupported()
+     * on your own).
+     */
+    public static doesSettingSupportLevel(settingName: string, level: SettingLevel): boolean {
+        const setting = SETTINGS[settingName];
+        if (!setting) {
+            throw new Error("Setting '" + settingName + "' does not appear to be a setting.");
+        }
+
+        return level === SettingLevel.DEFAULT || (setting.supportedLevels.includes(level));
+    }
+
     /**
      * Determines the first supported level out of all the levels that can be used for a
      * specific setting.