From ea45c6c841edff4d3db6c532217f9851678c29c7 Mon Sep 17 00:00:00 2001
From: Robert Nagy <ronagy@icloud.com>
Date: Thu, 15 Aug 2024 08:17:05 +0200
Subject: [PATCH] buffer: properly apply offset on fast path

Refs: https://github.com/nodejs/node/pull/54311#issuecomment-2290453437
PR-URL: https://github.com/nodejs/node/pull/54391
---
 src/node_buffer.cc | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/node_buffer.cc b/src/node_buffer.cc
index 0e1881eeb5f16d..9e7b634720f2bb 100644
--- a/src/node_buffer.cc
+++ b/src/node_buffer.cc
@@ -1479,9 +1479,10 @@ uint32_t FastWriteString(Local<Value> receiver,
   CHECK(offset <= dst.length());
   CHECK(dst.length() - offset <= std::numeric_limits<uint32_t>::max());
 
-  max_length = std::min<uint32_t>(dst.length() - offset, max_length);
+  const auto size = std::min(
+      {static_cast<uint32_t>(dst.length() - offset), max_length, src.length});
 
-  memcpy(dst_data, src.data, max_length);
+  memcpy(dst_data + offset, src.data, size);
 
   return max_length;
 }