Use safe DLL loading (avoid current directory) (#1293)

Author: oldnewthing

strings/base_activation.h

@@ -39,7 +39,7 @@ namespace winrt::impl
 
         if (hr == impl::error_not_initialized)
         {
-            auto usage = reinterpret_cast<int32_t(__stdcall*)(void** cookie) noexcept>(WINRT_IMPL_GetProcAddress(WINRT_IMPL_LoadLibraryW(L"combase.dll"), "CoIncrementMTAUsage"));
+            auto usage = reinterpret_cast<int32_t(__stdcall*)(void** cookie) noexcept>(WINRT_IMPL_GetProcAddress(load_library(L"combase.dll"), "CoIncrementMTAUsage"));
 
             if (!usage)
             {
@@ -66,7 +66,7 @@ namespace winrt::impl
         {
             path.resize(count);
             path += L".dll";
-            library_handle library(WINRT_IMPL_LoadLibraryW(path.c_str()));
+            library_handle library(load_library(path.c_str()));
             path.resize(path.size() - 4);
 
             if (!library)

strings/base_agile_ref.h

@@ -126,6 +126,11 @@ namespace winrt::impl
         atomic_ref_count m_references{ 1 };
     };
 
+    inline void* load_library(wchar_t const* library) noexcept
+    {
+        return WINRT_IMPL_LoadLibraryExW(library, nullptr, 0x00001000 /* LOAD_LIBRARY_SEARCH_DEFAULT_DIRS */);
+    }
+
     template <typename F, typename L>
     void load_runtime_function(wchar_t const* library, char const* name, F& result, L fallback) noexcept
     {
@@ -134,7 +139,7 @@ namespace winrt::impl
             return;
         }
 
-        result = reinterpret_cast<F>(WINRT_IMPL_GetProcAddress(WINRT_IMPL_LoadLibraryW(library), name));
+        result = reinterpret_cast<F>(WINRT_IMPL_GetProcAddress(load_library(library), name));
 
         if (result)
         {

strings/base_extern.h

@@ -24,7 +24,7 @@ __declspec(selectany) int32_t(__stdcall* winrt_activation_handler)(void* classId
 
 extern "C"
 {
-    void* __stdcall WINRT_IMPL_LoadLibraryW(wchar_t const* name) noexcept WINRT_IMPL_LINK(LoadLibraryW, 4);
+    void* __stdcall WINRT_IMPL_LoadLibraryExW(wchar_t const* name, void* unused, uint32_t flags) noexcept WINRT_IMPL_LINK(LoadLibraryExW, 12);
     int32_t __stdcall WINRT_IMPL_FreeLibrary(void* library) noexcept WINRT_IMPL_LINK(FreeLibrary, 4);
     void* __stdcall WINRT_IMPL_GetProcAddress(void* library, char const* name) noexcept WINRT_IMPL_LINK(GetProcAddress, 8);