Run the custom policy in a worker for security

Dockerfile

@@ -1,7 +1,7 @@
 FROM denoland/deno:1.43.3
 EXPOSE 4036
 WORKDIR /app
-RUN mkdir -p data && chown -R deno data
+RUN mkdir -p data/policy && chown -R deno data
 USER deno
 COPY . .
 RUN deno cache src/server.ts

data/.gitignore

@@ -1,2 +1,3 @@
 *
-!.gitignore
+!.gitignore
+!/policy

data/policy/.gitignore

@@ -0,0 +1,2 @@
+*
+!.gitignore

deno.json

@@ -13,7 +13,7 @@
     "admin:role": "deno run -A scripts/admin-role.ts",
     "stats:recompute": "deno run -A scripts/stats-recompute.ts"
   },
-  "unstable": ["ffi", "kv"],
+  "unstable": ["ffi", "kv", "worker-options"],
   "exclude": ["./public"],
   "imports": {
     "@/": "./src/",

src/config.ts

@@ -221,7 +221,7 @@ class Conf {
   }
   /** Path to the custom policy module. Must be an absolute path, https:, npm:, or jsr: URI. */
   static get policy(): string {
-    return Deno.env.get('DITTO_POLICY') || new URL('../data/policy.ts', import.meta.url).toString();
+    return Deno.env.get('DITTO_POLICY') || new URL('../data/policy.ts', import.meta.url).pathname;
   }
 }
 

src/pipeline.ts

@@ -16,6 +16,7 @@ import { Storages } from '@/storages.ts';
 import { getTagSet } from '@/tags.ts';
 import { eventAge, nostrDate, nostrNow, parseNip05, Time } from '@/utils.ts';
 import { fetchWorker } from '@/workers/fetch.ts';
+import { policyWorker } from '@/workers/policy.ts';
 import { TrendsWorker } from '@/workers/trends.ts';
 import { verifyEventWorker } from '@/workers/verify.ts';
 import { AdminSigner } from '@/signers/AdminSigner.ts';
@@ -62,11 +63,11 @@ async function policyFilter(event: NostrEvent): Promise<void> {
   ];
 
   try {
-    const CustomPolicy = (await import(Conf.policy)).default;
-    policies.push(new CustomPolicy());
+    await policyWorker.import(Conf.policy);
+    policies.push(policyWorker);
     debug(`Using custom policy: ${Conf.policy}`);
   } catch (e) {
-    if (e.code === 'ERR_MODULE_NOT_FOUND') {
+    if (e.message.includes('Module not found')) {
       debug('Custom policy not found <https://docs.soapbox.pub/ditto/policies/>');
     } else {
       console.error(`DITTO_POLICY (error importing policy): ${Conf.policy}`, e);

src/workers/policy.ts

@@ -0,0 +1,23 @@
+import * as Comlink from 'comlink';
+
+import { Conf } from '@/config.ts';
+import type { CustomPolicy } from '@/workers/policy.worker.ts';
+
+const policyDir = new URL('../../data/policy', import.meta.url).pathname;
+
+export const policyWorker = Comlink.wrap<CustomPolicy>(
+  new Worker(
+    new URL('./policy.worker.ts', import.meta.url),
+    {
+      type: 'module',
+      deno: {
+        permissions: {
+          read: [Conf.policy, policyDir],
+          write: [policyDir],
+          net: 'inherit',
+          env: false,
+        },
+      },
+    },
+  ),
+);

src/workers/policy.worker.ts

@@ -0,0 +1,19 @@
+import { NostrEvent, NostrRelayOK, NPolicy } from '@nostrify/nostrify';
+import { ReadOnlyPolicy } from '@nostrify/nostrify/policies';
+import * as Comlink from 'comlink';
+
+export class CustomPolicy implements NPolicy {
+  private policy: NPolicy = new ReadOnlyPolicy();
+
+  // deno-lint-ignore require-await
+  async call(event: NostrEvent): Promise<NostrRelayOK> {
+    return this.policy.call(event);
+  }
+
+  async import(path: string): Promise<void> {
+    const Policy = (await import(path)).default;
+    this.policy = new Policy();
+  }
+}
+
+Comlink.expose(new CustomPolicy());