fix(peer): grant forgery bug and stale comment

src/backend/controllers/peer/PeerController.ts

@@ -24,11 +24,7 @@ import { computeNetworkFingerprint } from '../../core/http/middleware/rateLimit.
 import type { PuterRouter } from '../../core/http/PuterRouter.js';
 import { PuterController } from '../types.js';
 import { PEER_COSTS } from './costs.js';
-import {
-    readClaimedGrantIdentifier,
-    signGuestGrant,
-    verifyGuestGrant,
-} from './guestGrant.js';
+import { signGuestGrant, verifyGuestGrant } from './guestGrant.js';
 import {
     DEFAULT_FREE_SUBSCRIPTION,
     DEFAULT_TEMP_SUBSCRIPTION,
@@ -191,19 +187,30 @@ export class PeerController extends PuterController {
                 // guests share one bucket and no host can be relayed for by
                 // more guests per minute than this — the only ceiling on guest
                 // spend we can apply before the bytes are already spent.
-                // A grant that doesn't parse can't name a bucket, so those
-                // requests fall back to the caller's own network.
+                // The limiter counts a request when it admits it, so only a
+                // grant that would redeem names a host; otherwise anyone
+                // holding the host's identifier could drain the bucket and
+                // lock out every real guest. Anything else - forged, expired,
+                // malformed, or no secret configured - is charged to the
+                // caller's own network.
                 rateLimit: {
                     scope: 'peer-guest-turn',
                     limit: 60,
                     window: 60_000,
                     key: (req: Request) => {
-                        const claimed = readClaimedGrantIdentifier(
-                            (req.body as { grant?: unknown } | undefined)
-                                ?.grant,
-                        );
-                        return claimed
-                            ? `host:${claimed}`
+                        const secret =
+                            this.config.peers?.guest_turn?.grant_secret;
+                        const verified = secret
+                            ? verifyGuestGrant({
+                                  grant: (
+                                      req.body as
+                                          { grant?: unknown } | undefined
+                                  )?.grant,
+                                  secret,
+                              })
+                            : null;
+                        return verified?.status === 'ok'
+                            ? `host:${verified.customIdentifier}`
                             : `net:${computeNetworkFingerprint(req)}`;
                     },
                 },

src/backend/controllers/peer/costs.ts

@@ -19,7 +19,7 @@
 
 import { toMicroCents } from '../../services/metering/utils';
 
-// Microcents per byte of TURN egress ($0.05/GB).
+// Microcents per byte of TURN egress ($0.10/GB).
 export const PEER_COSTS = {
     'turn:egress-bytes': toMicroCents(0.1 / 1000 ** 3),
 } as const;

src/backend/controllers/peer/guestGrant.test.ts

@@ -1,7 +1,6 @@
 import { createHmac } from 'node:crypto';
 import { describe, expect, it } from 'vitest';
 import {
-    readClaimedGrantIdentifier,
     signGuestGrant,
     verifyGuestGrant,
 } from './guestGrant.js';
@@ -243,59 +242,3 @@ describe('signGuestGrant / verifyGuestGrant', () => {
         });
     });
 });
-
-describe('readClaimedGrantIdentifier', () => {
-    it('reads the identifier from a valid grant', () => {
-        const { grant } = signGuestGrant({
-            customIdentifier: USER_ID,
-            ttlSeconds: 60,
-            secret: SECRET,
-        });
-
-        expect(readClaimedGrantIdentifier(grant)).toBe(USER_ID);
-    });
-
-    it('reads the claimed identifier without checking the signature', () => {
-        // Bucketing runs before verification, so this is expected: a forged
-        // grant still names a bucket, and the handler still rejects it.
-        const grant = forgeGrant(
-            { id: USER_ID, exp: 9_999_999_999, n: 'x' },
-            { secret: 'wrong-secret' },
-        );
-
-        expect(readClaimedGrantIdentifier(grant)).toBe(USER_ID);
-    });
-
-    it('reads an expired grant, which the handler then rejects', () => {
-        const { grant } = signGuestGrant({
-            customIdentifier: USER_ID,
-            ttlSeconds: 60,
-            secret: SECRET,
-            now: 1_000_000_000_000,
-        });
-
-        expect(readClaimedGrantIdentifier(grant)).toBe(USER_ID);
-        expect(verifyGuestGrant({ grant, secret: SECRET })).toEqual({
-            status: 'expired',
-        });
-    });
-
-    it.each([
-        ['a non-string', 42],
-        ['undefined', undefined],
-        ['a wrong-shaped string', 'not-a-grant'],
-        ['an unknown version', 'pg2.abc.def'],
-        ['an over-long string', `pg1.${'a'.repeat(600)}.sig`],
-        [
-            'a non-JSON payload',
-            `pg1.${Buffer.from('x').toString('base64url')}.sig`,
-        ],
-    ])('returns null for %s', (_label, grant) => {
-        expect(readClaimedGrantIdentifier(grant)).toBeNull();
-    });
-
-    it('returns null for an identifier of the wrong shape', () => {
-        const grant = forgeGrant({ id: 'nope', exp: 9_999_999_999 });
-        expect(readClaimedGrantIdentifier(grant)).toBeNull();
-    });
-});

src/backend/controllers/peer/guestGrant.ts

@@ -171,37 +171,3 @@ export const verifyGuestGrant = ({
         expiresAt: payload.exp,
     };
 };
-
-/**
- * Read the claimed identifier out of a grant _without_ verifying it, for
- * rate-limit bucketing only.
- *
- * Bucketing has to happen before the handler runs, and a forged grant is
- * rejected there without reaching the upstream API — so an unverified read is
- * enough to put a host's guests in one bucket, and the worst a forger achieves
- * is choosing which bucket their own rejections land in. Never use this to
- * decide attribution.
- *
- * @returns The claimed identifier, or null if the grant doesn't parse.
- */
-export const readClaimedGrantIdentifier = (grant: unknown): string | null => {
-    if (typeof grant !== 'string' || grant.length > MAX_GRANT_LENGTH) {
-        return null;
-    }
-    const parts = grant.split('.');
-    if (parts.length !== 3 || parts[0] !== GRANT_VERSION) return null;
-    try {
-        const payload = JSON.parse(
-            Buffer.from(parts[1]!, 'base64url').toString('utf8'),
-        ) as { id?: unknown };
-        if (
-            typeof payload?.id !== 'string' ||
-            !IDENTIFIER_RE.test(payload.id)
-        ) {
-            return null;
-        }
-        return payload.id;
-    } catch {
-        return null;
-    }
-};