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fix(crypto): request persistent storage on client init (KE-1 mitigation)

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The IndexedDB crypto store is evictable while the localStorage session survives,
so the browser can drop it out from under a live login -> the device resurrects
with a blank key store and re-uploads a one-time key at an id Synapse already
holds -> a permanent '400 M_UNKNOWN: One time key ... already exists' upload
storm (and undecryptable to-device/media keys downstream).

initClient now calls navigator.storage.persist() before creating the crypto
store, so the origin's storage is marked persistent and won't be evicted.
Best-effort (granted by engagement/PWA-install, no prompt; denial is non-fatal).
Preventive only -- an already-diverged device still needs a clean re-login.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Jared Vititoe
2026-07-07 20:18:32 -04:00
parent fd87a27251
commit 45afc9ba7e
1 changed files with 26 additions and 0 deletions
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src/client/initMatrix.ts
+26
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@@ -12,7 +12,33 @@ import { deleteSearchCacheDatabase } from '../app/utils/searchCache';
// This happens after a downgrade (e.g. matrix-js-sdk was briefly upgraded and then reverted).
export const IDB_VERSION_CONFLICT = 'IDB_VERSION_CONFLICT';
/**
* KE-1 mitigation. Ask the browser to make this origin's storage persistent so the
* IndexedDB **crypto store** isn't evicted from under a surviving `localStorage`
* session. When that happens the device "resurrects" with a blank key store and the
* client re-uploads a one-time key at an id Synapse already holds → a permanent
* `400 M_UNKNOWN: … already exists` upload-conflict storm (and, downstream,
* undecryptable to-device/media keys). `persist()` grants based on engagement / PWA
* install and shows no prompt; denial/absence is non-fatal.
*/
export const requestPersistentStorage = async (): Promise<boolean> => {
try {
if (!navigator.storage?.persist) return false;
if (await navigator.storage.persisted()) return true;
const granted = await navigator.storage.persist();
if (!granted) {
console.warn('Persistent storage not granted — the crypto store remains evictable (KE-1).');
}
return granted;
} catch {
return false;
}
};
export const initClient = async (session: Session): Promise<MatrixClient> => {
// Protect the crypto store from eviction before we create and write to it.
await requestPersistentStorage();
const indexedDBStore = new IndexedDBStore({
indexedDB: globalThis.indexedDB,
localStorage: globalThis.localStorage,