collector: release HCS result documents on operation failure (#2600)

Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

internal/headers/hcs/operation_result_test.go

@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: Apache-2.0
+//
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build windows
+
+package hcs
+
+import (
+	"testing"
+	"unsafe"
+
+	"github.com/stretchr/testify/require"
+	"golang.org/x/sys/windows"
+)
+
+func TestOperationResultDocumentCleanup(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		name     string
+		result   uintptr
+		document bool
+	}{
+		{"successful document", 0, true},
+		{"successful empty", 0, false},
+		{"failure diagnostic", 0x80070005, true},
+		{"failure empty", 0x80070005, false},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			var document *uint16
+			if tc.document {
+				encoded, err := windows.UTF16FromString("diagnostic")
+				require.NoError(t, err)
+
+				document = &encoded[0]
+			}
+
+			releases := 0
+			release := func(pointer unsafe.Pointer) {
+				require.Equal(t, unsafe.Pointer(document), pointer)
+
+				releases++
+			}
+
+			result, err := consumeOperationResult(tc.result, document, release)
+			if tc.result != 0 {
+				require.ErrorIs(t, err, windows.ERROR_ACCESS_DENIED)
+				require.Empty(t, result)
+			} else {
+				require.NoError(t, err)
+
+				if tc.document {
+					require.Equal(t, "diagnostic", result)
+				} else {
+					require.Empty(t, result)
+				}
+			}
+
+			if tc.document {
+				require.Equal(t, 1, releases)
+			} else {
+				require.Zero(t, releases)
+			}
+		})
+	}
+}

internal/headers/hcs/syscall.go

@@ -60,14 +60,22 @@ func WaitForOperationResult(operation Operation, timeout uint32) (string, error)
 	var resultDocument *uint16
 
 	r1, _, _ := procHcsWaitForOperationResult.Call(uintptr(operation), uintptr(timeout), uintptr(unsafe.Pointer(&resultDocument)))
-	if r1 != 0 {
-		return "", fmt.Errorf("HcsWaitForOperationResult failed: HRESULT 0x%X: %w", r1, Win32FromHResult(r1))
+
+	return consumeOperationResult(r1, resultDocument, windows.CoTaskMemFree)
+}
+
+// consumeOperationResult releases every caller-owned result document, including
+// the diagnostic documents returned by failed operations.
+func consumeOperationResult(resultCode uintptr, resultDocument *uint16, release func(unsafe.Pointer)) (string, error) {
+	if resultDocument != nil {
+		defer release(unsafe.Pointer(resultDocument))
 	}
 
-	result := windows.UTF16PtrToString(resultDocument)
-	windows.CoTaskMemFree(unsafe.Pointer(resultDocument))
+	if resultCode != 0 {
+		return "", fmt.Errorf("HcsWaitForOperationResult failed: HRESULT 0x%X: %w", resultCode, Win32FromHResult(resultCode))
+	}
 
-	return result, nil
+	return windows.UTF16PtrToString(resultDocument), nil
 }
 
 // CloseOperation closes an operation.