From cfcb23d0da5893a7dd4c88bce8b4ca1798e5c645 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marie=20P=C3=ADchov=C3=A1?= <mapichov@microsoft.com>
Date: Tue, 3 Mar 2020 17:07:08 +0100
Subject: [PATCH] Fixed heap corruption by ensuring that FreeHGlobal is called
 only once even in multi-threaded and multiple Dispose calls.

---
 .../src/System/Net/Windows/RequestContextBase.cs           | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/libraries/System.Net.HttpListener/src/System/Net/Windows/RequestContextBase.cs b/src/libraries/System.Net.HttpListener/src/System/Net/Windows/RequestContextBase.cs
index c92a66840df5c5..9dfab0c8447d50 100644
--- a/src/libraries/System.Net.HttpListener/src/System/Net/Windows/RequestContextBase.cs
+++ b/src/libraries/System.Net.HttpListener/src/System/Net/Windows/RequestContextBase.cs
@@ -4,6 +4,7 @@
 
 using System.Diagnostics;
 using System.Runtime.InteropServices;
+using System.Threading;
 
 namespace System.Net
 {
@@ -49,10 +50,10 @@ public void Dispose()
 
         protected virtual void Dispose(bool disposing)
         {
-            if (_backingBuffer != IntPtr.Zero)
+            IntPtr backingBuffer = Interlocked.Exchange(ref _backingBuffer, IntPtr.Zero);
+            if (backingBuffer != IntPtr.Zero)
             {
-                Marshal.FreeHGlobal(_backingBuffer);
-                _backingBuffer = IntPtr.Zero;
+                Marshal.FreeHGlobal(backingBuffer);
             }
         }