From 7c2870d5f367ec57e5319a716e1a8bca944a8029 Mon Sep 17 00:00:00 2001
From: cjihrig <cjihrig@gmail.com>
Date: Thu, 30 Apr 2020 22:04:03 -0400
Subject: [PATCH] wasi: avoid hard crash if start() is never called

Prior to this commit, calling the WebAssembly instance's _start()
export directly would hard crash the process because the memory
was never configured. This commit adds an additional check that
the memory is usable. With this commit, calling _start() directly
will still lead to WASI exiting with a non-zero exit code, but
Node does not crash.
---
 src/node_wasi.cc                |  8 ++++----
 test/wasi/test-no-start-call.js | 35 +++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 4 deletions(-)
 create mode 100644 test/wasi/test-no-start-call.js

diff --git a/src/node_wasi.cc b/src/node_wasi.cc
index 0330656b29e926..3ad666cce2506d 100644
--- a/src/node_wasi.cc
+++ b/src/node_wasi.cc
@@ -1791,11 +1791,11 @@ uvwasi_errno_t WASI::backingStore(char** store, size_t* byte_length) {
   Local<Object> memory = PersistentToLocal::Strong(this->memory_);
   Local<Value> prop;
 
-  if (!memory->Get(env->context(), env->buffer_string()).ToLocal(&prop))
-    return UVWASI_EINVAL;
-
-  if (!prop->IsArrayBuffer())
+  if (this->memory_.IsEmpty() ||
+      !memory->Get(env->context(), env->buffer_string()).ToLocal(&prop) ||
+      !prop->IsArrayBuffer()) {
     return UVWASI_EINVAL;
+  }
 
   Local<ArrayBuffer> ab = prop.As<ArrayBuffer>();
   std::shared_ptr<BackingStore> backing_store = ab->GetBackingStore();
diff --git a/test/wasi/test-no-start-call.js b/test/wasi/test-no-start-call.js
new file mode 100644
index 00000000000000..e7fc23c75115de
--- /dev/null
+++ b/test/wasi/test-no-start-call.js
@@ -0,0 +1,35 @@
+'use strict';
+const common = require('../common');
+
+if (process.argv[2] === 'child') {
+  (async () => {
+    const fs = require('fs');
+    const path = require('path');
+    const { WASI } = require('wasi');
+    const wasmDir = path.join(__dirname, 'wasm');
+    const modulePath = path.join(wasmDir, 'main_args.wasm');
+    const buffer = fs.readFileSync(modulePath);
+    const wasi = new WASI();
+    const importObject = { wasi_snapshot_preview1: wasi.wasiImport };
+    const { instance } = await WebAssembly.instantiate(buffer, importObject);
+
+    // Verify that calling the _start() export instead of start() does not
+    // crash. The application will fail with a non-zero exit code.
+    instance.exports._start();
+  })().then(common.mustCall());
+} else {
+  const assert = require('assert');
+  const { spawnSync } = require('child_process');
+  const child = spawnSync(process.execPath, [
+    '--experimental-wasi-unstable-preview1',
+    '--experimental-wasm-bigint',
+    '--no-warnings',
+    __filename,
+    'child'
+  ]);
+
+  assert.strictEqual(child.stdout.toString(), '');
+  assert.strictEqual(child.stderr.toString(), '');
+  assert.strictEqual(child.signal, null);
+  assert.notStrictEqual(child.status, 0);
+}