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fix(security): cache device salt in-process to survive fs-unwritable

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getDeviceSalt returned a new randomBytes(16) on every call when the
salt file couldn't be persisted (read-only home, disk full). That
broke correlation: two attacks with identical payloads from the same
session would hash different, defeating both the cross-device
rainbow-table protection and the dashboard's top-attack aggregation.

Cache the salt in a module-level variable on first generation. If
persistence fails, the in-memory value holds for the process lifetime.
Next process gets a new salt, but within-session correlation works.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Garry Tan
2026-04-20 07:17:23 +08:00
parent 7f7249d3d2
commit 905d5a2e29
1 changed files with 20 additions and 10 deletions
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browse/src/security.ts
+20 -10
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@@ -107,11 +107,12 @@ export function combineVerdict(signals: LayerSignal[]): SecurityResult {
const mlHighSignals = [content, deberta, transcript].filter(c => c >= THRESHOLDS.WARN);
const hasDebertaSignal = deberta > 0;
// Ensemble rule:
// * 2-of-3 ML classifiers >= WARN → BLOCK when DeBERTa is in the pool
// * 2-of-2 (content + transcript) >= WARN → BLOCK when DeBERTa disabled
// In both cases, cross-model agreement is what upgrades from WARN to BLOCK.
const requiredForBlock = hasDebertaSignal ? 2 : 2;
// Ensemble rule: cross-model agreement is what upgrades from WARN to BLOCK.
// Requires >= 2 ML classifiers at WARN regardless of whether DeBERTa is
// in the pool (hasDebertaSignal kept in scope for future threshold tuning,
// but today the count-based rule is 2 in both configurations).
void hasDebertaSignal;
const requiredForBlock = 2;
if (mlHighSignals.length >= requiredForBlock) {
return {
verdict: 'block',
@@ -223,22 +224,31 @@ const MAX_LOG_GENERATIONS = 5;
* ~/.gstack/security/device-salt (0600). Random per-device, prevents rainbow
* table attacks across devices (Codex tier-2 finding).
*/
let cachedSalt: string | null = null;
function getDeviceSalt(): string {
if (cachedSalt) return cachedSalt;
try {
if (fs.existsSync(SALT_FILE)) return fs.readFileSync(SALT_FILE, 'utf8').trim();
if (fs.existsSync(SALT_FILE)) {
cachedSalt = fs.readFileSync(SALT_FILE, 'utf8').trim();
return cachedSalt;
}
} catch {
// fall through to generate
}
try {
fs.mkdirSync(SECURITY_DIR, { recursive: true, mode: 0o700 });
} catch {}
const salt = randomBytes(16).toString('hex');
cachedSalt = randomBytes(16).toString('hex');
try {
fs.writeFileSync(SALT_FILE, salt, { mode: 0o600 });
fs.writeFileSync(SALT_FILE, cachedSalt, { mode: 0o600 });
} catch {
// Non-fatal: we still return salt, just can't persist. Next call regenerates.
// Can't persist (read-only fs, disk full). Keep the in-memory salt
// for this process so cross-log correlation still works within a
// session. Next process gets a new salt, but that's a degraded-mode
// acceptable cost.
}
return salt;
return cachedSalt;
}
export function hashPayload(payload: string): string {