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Commit 1851cf4

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jasnelltargos
jasnell
authored and
targos
committed
doc, test: document and test vm timeout escapes
Using `process.nextTick()`, `Promise`, or `queueMicrotask()`, it is possible to escape the `timeout` set when running code with `vm.runInContext()`, `vm.runInThisContext()`, and `vm.runInNewContext()`. This documents the issue and adds three known_issues tests. Refs: #3020 PR-URL: #23743 Refs: #3020 Reviewed-By: Luigi Pinca <luigipinca@gmail.com> Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
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‎doc/api/vm.md‎

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@@ -962,6 +962,38 @@ within which it can operate. The process of creating the V8 Context and
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associating it with the `sandbox` object is what this document refers to as
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"contextifying" the `sandbox`.
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## Timeout limitations when using process.nextTick(), Promises, and queueMicrotask()
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Because of the internal mechanics of how the `process.nextTick()` queue and
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the microtask queue that underlies Promises are implemented within V8 and
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Node.js, it is possible for code running within a context to "escape" the
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`timeout` set using `vm.runInContext()`, `vm.runInNewContext()`, and
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`vm.runInThisContext()`.
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For example, the following code executed by `vm.runInNewContext()` with a
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timeout of 5 milliseconds schedules an infinite loop to run after a promise
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resolves. The scheduled loop is never interrupted by the timeout:
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```js
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const vm = require('vm');
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function loop() {
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while (1) console.log(Date.now());
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}
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vm.runInNewContext(
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'Promise.resolve().then(loop);',
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{ loop, console },
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{ timeout: 5 }
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);
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```
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This issue also occurs when the `loop()` call is scheduled using
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the `process.nextTick()` and `queueMicrotask()` functions.
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This issue occurs because all contexts share the same microtask and nextTick
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queues.
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[`Error`]: errors.html#errors_class_error
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[`ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING`]: errors.html#ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING
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[`URL`]: url.html#url_class_url
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‎test/known_issues/test-vm-timeout-escape-nexttick.js‎

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'use strict';
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// https://github.com/nodejs/node/issues/3020
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// Promises, nextTick, and queueMicrotask allow code to escape the timeout
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// set for runInContext, runInNewContext, and runInThisContext
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require('../common');
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const assert = require('assert');
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const vm = require('vm');
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const NS_PER_MS = 1000000n;
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const hrtime = process.hrtime.bigint;
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const nextTick = process.nextTick;
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function loop() {
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const start = hrtime();
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while (1) {
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const current = hrtime();
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const span = (current - start) / NS_PER_MS;
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if (span >= 100n) {
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throw new Error(
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`escaped timeout at ${span} milliseconds!`);
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}
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}
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}
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assert.throws(() => {
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vm.runInNewContext(
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'nextTick(loop); loop();',
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{
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hrtime,
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nextTick,
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loop
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},
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{ timeout: 5 }
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);
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}, {
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code: 'ERR_SCRIPT_EXECUTION_TIMEOUT',
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message: 'Script execution timed out after 5ms'
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});
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‎test/known_issues/test-vm-timeout-escape-promise.js‎

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'use strict';
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// https://github.com/nodejs/node/issues/3020
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// Promises, nextTick, and queueMicrotask allow code to escape the timeout
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// set for runInContext, runInNewContext, and runInThisContext
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require('../common');
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const assert = require('assert');
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const vm = require('vm');
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const NS_PER_MS = 1000000n;
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const hrtime = process.hrtime.bigint;
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function loop() {
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const start = hrtime();
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while (1) {
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const current = hrtime();
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const span = (current - start) / NS_PER_MS;
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if (span >= 100n) {
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throw new Error(
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`escaped timeout at ${span} milliseconds!`);
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}
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}
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}
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assert.throws(() => {
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vm.runInNewContext(
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'Promise.resolve().then(loop); loop();',
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{
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hrtime,
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loop
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},
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{ timeout: 5 }
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);
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}, {
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code: 'ERR_SCRIPT_EXECUTION_TIMEOUT',
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message: 'Script execution timed out after 5ms'
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});
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‎test/known_issues/test-vm-timeout-escape-queuemicrotask.js‎

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'use strict';
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// https://github.com/nodejs/node/issues/3020
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// Promises, nextTick, and queueMicrotask allow code to escape the timeout
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// set for runInContext, runInNewContext, and runInThisContext
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require('../common');
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const assert = require('assert');
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const vm = require('vm');
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const NS_PER_MS = 1000000n;
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const hrtime = process.hrtime.bigint;
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function loop() {
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const start = hrtime();
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while (1) {
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const current = hrtime();
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const span = (current - start) / NS_PER_MS;
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if (span >= 100n) {
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throw new Error(
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`escaped timeout at ${span} milliseconds!`);
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}
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}
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}
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assert.throws(() => {
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vm.runInNewContext(
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'queueMicrotask(loop); loop();',
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{
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hrtime,
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queueMicrotask,
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loop
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},
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{ timeout: 5 }
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);
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}, {
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code: 'ERR_SCRIPT_EXECUTION_TIMEOUT',
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message: 'Script execution timed out after 5ms'
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});

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