From 9c56134978403ff7edeac12d21a2fb39cfba8e3e Mon Sep 17 00:00:00 2001
From: Anna Henningsen <anna@addaleax.net>
Date: Wed, 30 Sep 2020 11:55:59 +0200
Subject: [PATCH] src: make MakeCallback() check can_call_into_js before
 getting method
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There is a check for this in the inner `MakeCallback()` function
called by it, but since the `Get()` call here can also result in a
call into JS, we should ideally check the flag before that.

PR-URL: https://github.com/nodejs/node/pull/35424
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Denys Otrishko <shishugi@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Andrey Pechkurov <apechkurov@gmail.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>
---
 src/api/callback.cc | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/api/callback.cc b/src/api/callback.cc
index 84664c089594eb..3d4f91a866ea39 100644
--- a/src/api/callback.cc
+++ b/src/api/callback.cc
@@ -223,10 +223,19 @@ MaybeLocal<Value> MakeCallback(Isolate* isolate,
                                int argc,
                                Local<Value> argv[],
                                async_context asyncContext) {
-  Local<Value> callback_v =
-      recv->Get(isolate->GetCurrentContext(), symbol).ToLocalChecked();
-  if (callback_v.IsEmpty()) return Local<Value>();
-  if (!callback_v->IsFunction()) return Local<Value>();
+  // Check can_call_into_js() first because calling Get() might do so.
+  Environment* env = Environment::GetCurrent(recv->CreationContext());
+  CHECK_NOT_NULL(env);
+  if (!env->can_call_into_js()) return Local<Value>();
+
+  Local<Value> callback_v;
+  if (!recv->Get(isolate->GetCurrentContext(), symbol).ToLocal(&callback_v))
+    return Local<Value>();
+  if (!callback_v->IsFunction()) {
+    // This used to return an empty value, but Undefined() makes more sense
+    // since no exception is pending here.
+    return Undefined(isolate);
+  }
   Local<Function> callback = callback_v.As<Function>();
   return MakeCallback(isolate, recv, callback, argc, argv, asyncContext);
 }