From 8d68062cc4dc34d63bd4e614d818f7c415a10251 Mon Sep 17 00:00:00 2001
From: Justin Kotalik <jkotalik12@gmail.com>
Date: Mon, 5 Aug 2019 08:51:55 -0700
Subject: [PATCH] Always load hostfxr.dll by absolute path (#12807)

---
 .../AspNetCoreModuleV2/CommonLib/HostFxr.cpp  | 19 ++++++++++++-------
 .../AspNetCoreModuleV2/CommonLib/HostFxr.h    |  1 -
 .../inprocessapplication.cpp                  |  2 +-
 3 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxr.cpp b/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxr.cpp
index b05a4d1a50..545791610b 100644
--- a/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxr.cpp
+++ b/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxr.cpp
@@ -30,16 +30,17 @@ void HostFxrErrorRedirector::HostFxrErrorRedirectorCallback(const WCHAR* message
     m_writeFunction->Append(std::wstring(message) + L"\r\n");
 }
 
-void HostFxr::Load()
-{
-    HMODULE hModule;
-    THROW_LAST_ERROR_IF(!GetModuleHandleEx(0, L"hostfxr.dll", &hModule));
-    Load(hModule);
-}
-
 void HostFxr::Load(HMODULE moduleHandle)
 {
+    // A hostfxr may already be loaded here if we tried to start with an
+    // invalid configuration. Release hostfxr before loading it again.
+    if (m_hHostFxrDll != nullptr)
+    {
+        m_hHostFxrDll.release();
+    }
+
     m_hHostFxrDll = moduleHandle;
+
     try
     {
         m_hostfxr_get_native_search_directories_fn = ModuleHelpers::GetKnownProcAddress<hostfxr_get_native_search_directories_fn>(moduleHandle, "hostfxr_get_native_search_directories");
@@ -63,9 +64,13 @@ void HostFxr::Load(HMODULE moduleHandle)
 
 void HostFxr::Load(const std::wstring& location)
 {
+    // Make sure to always load hostfxr via an absolute path.
+    // If the process fails to start for whatever reason, a mismatched hostfxr
+    // may be already loaded in the process.
     try
     {
         HMODULE hModule;
+        LOG_INFOF(L"Loading hostfxr from location %s", location.c_str());
         THROW_LAST_ERROR_IF_NULL(hModule = LoadLibraryW(location.c_str()));
         Load(hModule);
     }
diff --git a/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxr.h b/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxr.h
index 526222322e..ced4dd1940 100644
--- a/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxr.h
+++ b/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxr.h
@@ -60,7 +60,6 @@ public:
     {
     }
 
-    void Load();
     void Load(HMODULE moduleHandle);
     void Load(const std::wstring& location);
 
diff --git a/src/Servers/IIS/AspNetCoreModuleV2/InProcessRequestHandler/inprocessapplication.cpp b/src/Servers/IIS/AspNetCoreModuleV2/InProcessRequestHandler/inprocessapplication.cpp
index 5707e4cd77..b671e7dba2 100644
--- a/src/Servers/IIS/AspNetCoreModuleV2/InProcessRequestHandler/inprocessapplication.cpp
+++ b/src/Servers/IIS/AspNetCoreModuleV2/InProcessRequestHandler/inprocessapplication.cpp
@@ -210,7 +210,7 @@ IN_PROCESS_APPLICATION::ExecuteApplication()
 
             hostFxrResolutionResult->GetArguments(context->m_argc, context->m_argv);
             THROW_IF_FAILED(SetEnvironmentVariablesOnWorkerProcess());
-            context->m_hostFxr.Load();
+            context->m_hostFxr.Load(hostFxrResolutionResult->GetHostFxrLocation());
         }
         else
         {