From efc393625496a7467550edfbc4af4bde3aaeff1f Mon Sep 17 00:00:00 2001
From: Paul Bouchon <mail@bitpshr.net>
Date: Thu, 27 Aug 2026 08:51:13 -0400
Subject: [PATCH] src: disable V8 external memory reasonable size check

V8 aborts the process when external memory grows by more than
--external-memory-max-reasonable-size gigabytes in a single step. The
32 GB default is a Chromium-oriented sanity check; allocating a buffer
larger than that is legitimate in Node and should raise a RangeError
rather than terminate the process.

Default the flag to 0 unless the user supplied a value, alongside the
other V8 defaults Node sets explicitly.

Fixes: https://github.com/nodejs/node/issues/65534
Signed-off-by: Paul Bouchon <mail@bitpshr.net>
---
 src/node.cc                                   | 14 ++++++++
 .../test-external-memory-reasonable-size.js   | 33 +++++++++++++++++++
 2 files changed, 47 insertions(+)
 create mode 100644 test/parallel/test-external-memory-reasonable-size.js

diff --git a/src/node.cc b/src/node.cc
index 5e00996c1ba3..b4e8cdaf2aaa 100644
--- a/src/node.cc
+++ b/src/node.cc
@@ -777,6 +777,20 @@ static ExitCode ProcessGlobalArgsInternal(std::vector<std::string>* args,
     v8_args.emplace_back("--js-source-phase-imports");
   }
 
+  // V8 aborts the process when external memory grows by more than
+  // --external-memory-max-reasonable-size gigabytes in a single step. That
+  // limit is a Chromium-oriented sanity check; allocating a buffer larger
+  // than it is a legitimate thing to do in Node, and should raise a
+  // RangeError rather than crash. Disable the check unless the user asked
+  // for a specific limit.
+  // Refs: https://github.com/nodejs/node/issues/65534
+  if (std::ranges::none_of(v8_args, [](const std::string& arg) {
+        return arg.starts_with("--external-memory-max-reasonable-size") ||
+               arg.starts_with("--external_memory_max_reasonable_size");
+      })) {
+    v8_args.emplace_back("--external-memory-max-reasonable-size=0");
+  }
+
 #ifdef __POSIX__
   // Block SIGPROF signals when sleeping in epoll_wait/kevent/etc.  Avoids the
   // performance penalty of frequent EINTR wakeups when the profiler is running.
diff --git a/test/parallel/test-external-memory-reasonable-size.js b/test/parallel/test-external-memory-reasonable-size.js
new file mode 100644
index 000000000000..14e2573328ba
--- /dev/null
+++ b/test/parallel/test-external-memory-reasonable-size.js
@@ -0,0 +1,33 @@
+'use strict';
+
+// V8 aborts the process when external memory grows by more than
+// --external-memory-max-reasonable-size gigabytes in a single step. Node
+// disables that check by default, but an explicit value on the command line
+// must still be honored.
+// Refs: https://github.com/nodejs/node/issues/65534
+
+const common = require('../common');
+const assert = require('assert');
+const { spawnSync } = require('child_process');
+const { totalmem } = require('os');
+
+// The smallest limit V8 accepts is 1 GB, so the child has to allocate more
+// than that before the check can fire.
+if (totalmem() < 4 * 1024 ** 3)
+  common.skip('not enough memory to exceed a 1 GB external memory limit');
+
+for (const flag of [
+  '--external-memory-max-reasonable-size=1',
+  '--external_memory_max_reasonable_size=1',
+]) {
+  const child = spawnSync(process.execPath, [
+    flag, '-e', 'new Float64Array(150_000_000)',
+  ]);
+
+  assert.notStrictEqual(
+    child.status,
+    0,
+    `${flag} was not honored, the child exited cleanly`,
+  );
+  assert.match(child.stderr.toString(), /kMaxReasonableBytes/);
+}