Fix E_ACCESSDENIED during download if temp is hidden

src/windows/common/wslutil.cpp

@@ -368,8 +368,20 @@ std::wstring wsl::windows::common::wslutil::DownloadFileImpl(
         Filename = Url.substr(lastSlash + 1);
     }
 
-    const auto downloadFolder =
-        winrt::Windows::Storage::StorageFolder::GetFolderFromPathAsync(std::filesystem::temp_directory_path().wstring()).get();
+    // GetFolderFromPathAsync does not accept hidden or system path.
+    // To avoid the temp path having those attributes (mainly hidden),
+    // we need to create a subfolder without those attributes.
+    auto downloadFolderPath = std::filesystem::temp_directory_path() / L"wsl-downloads";
+    std::filesystem::create_directories(downloadFolderPath);
+
+    const auto attributes = GetFileAttributesW(downloadFolderPath.c_str());
+    THROW_LAST_ERROR_IF(attributes == INVALID_FILE_ATTRIBUTES);
+    if (attributes & (FILE_ATTRIBUTE_HIDDEN | FILE_ATTRIBUTE_SYSTEM))
+    {
+        THROW_IF_WIN32_BOOL_FALSE(SetFileAttributesW(downloadFolderPath.c_str(), attributes & ~(FILE_ATTRIBUTE_HIDDEN | FILE_ATTRIBUTE_SYSTEM)));
+    }
+
+    const auto downloadFolder = winrt::Windows::Storage::StorageFolder::GetFolderFromPathAsync(downloadFolderPath.wstring()).get();
 
     const auto file =
         downloadFolder.CreateFileAsync(Filename, winrt::Windows::Storage::CreationCollisionOption::GenerateUniqueName).get();

test/windows/Common.cpp

@@ -2474,14 +2474,32 @@ void Trim(std::wstring& string)
     std::erase_if(string, [](auto c) { return !isalnum(c); });
 }
 
-ScopedEnvVariable::ScopedEnvVariable(const std::wstring& Name, const std::wstring& Value) : m_name(Name)
+ScopedEnvVariable::ScopedEnvVariable(const std::wstring& Name, const std::wstring& Value, bool restore) : m_name(Name)
 {
+    if (restore)
+    {
+        std::wstring value;
+        const auto result = wil::GetEnvironmentVariableW(Name.c_str(), value);
+        if (result != HRESULT_FROM_WIN32(ERROR_ENVVAR_NOT_FOUND))
+        {
+            VERIFY_SUCCEEDED(result);
+            m_originalValue = std::move(value);
+        }
+    }
+
     VERIFY_IS_TRUE(SetEnvironmentVariable(Name.c_str(), Value.c_str()));
 }
 
 ScopedEnvVariable::~ScopedEnvVariable()
 {
-    VERIFY_IS_TRUE(SetEnvironmentVariable(m_name.c_str(), nullptr));
+    if (m_originalValue.has_value())
+    {
+        VERIFY_IS_TRUE(SetEnvironmentVariable(m_name.c_str(), m_originalValue->c_str()));
+    }
+    else
+    {
+        VERIFY_IS_TRUE(SetEnvironmentVariable(m_name.c_str(), nullptr));
+    }
 }
 
 UniqueWebServer::UniqueWebServer(LPCWSTR Endpoint, LPCWSTR Content)

test/windows/Common.h

@@ -309,16 +309,15 @@ class RegistryKeyChange
 class ScopedEnvVariable
 {
 public:
-    ScopedEnvVariable(const std::wstring& Name, const std::wstring& Value);
+    ScopedEnvVariable(const std::wstring& Name, const std::wstring& Value, bool restore = false);
     ~ScopedEnvVariable();
 
-    ScopedEnvVariable(const WslConfigChange&) = delete;
-    ScopedEnvVariable(WslConfigChange&&) = delete;
-    const ScopedEnvVariable& operator=(ScopedEnvVariable&&) = delete;
-    const ScopedEnvVariable& operator=(ScopedEnvVariable&) = delete;
+    NON_COPYABLE(ScopedEnvVariable);
+    NON_MOVABLE(ScopedEnvVariable);
 
 private:
     std::wstring m_name;
+    std::optional<std::wstring> m_originalValue{std::nullopt};
 };
 
 class UniqueWebServer

test/windows/UnitTests.cpp

@@ -5143,7 +5143,7 @@ Error code: Wsl/Service/RegisterDistro/E_INVALIDARG\r\n";
             wsl::shared::string::MultiByteToWide("01:23:45:67:89:AB"));
     }
 
-    TEST_METHOD(ModernDistroInstall)
+    static void ModernDistroInstallImpl()
     {
         auto tarPath = "file://" + wsl::shared::string::WideToMultiByte(EscapePath(g_testDistroPath));
 
@@ -5779,6 +5779,31 @@ Error code: Wsl/InstallDistro/WSL_E_INVALID_JSON\r\n",
         }
     }
 
+    TEST_METHOD(ModernDistroInstall)
+    {
+        ModernDistroInstallImpl();
+    }
+
+    TEST_METHOD(ModernDistroInstallWithHiddenTempFolder)
+    {
+        // Avoid contaminating the real temp folder.
+        const auto testTempFolder = std::filesystem::temp_directory_path() / L"wsl-install-test";
+        std::filesystem::create_directories(testTempFolder);
+        auto cleanupTempFolder = wil::scope_exit_log(WI_DIAGNOSTICS_INFO, [&] {
+            std::error_code error;
+            std::filesystem::remove_all(testTempFolder, error);
+        });
+
+        const auto originalAttributes = GetFileAttributesW(testTempFolder.c_str());
+        VERIFY_IS_TRUE(originalAttributes != INVALID_FILE_ATTRIBUTES);
+        VERIFY_IS_TRUE(SetFileAttributesW(testTempFolder.c_str(), originalAttributes | FILE_ATTRIBUTE_HIDDEN));
+
+        ScopedEnvVariable temp(L"TEMP", testTempFolder.wstring(), true);
+        ScopedEnvVariable tmp(L"TMP", testTempFolder.wstring(), true);
+
+        ModernDistroInstallImpl();
+    }
+
     TEST_METHOD(ModernInstallEndToEnd)
     {
         constexpr auto tarName = L"end2end.tar";