fix(auth): harden restore verification transaction

tools/tht/internal/backup/restore_file_windows_test.go

@@ -0,0 +1,83 @@
+//go:build windows
+
+package backup
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/aritmolab/thothii/tools/tht/internal/safeio"
+)
+
+func TestReplaceRestoreFileWindowsCreatesAndReplacesOwnerOnlyRegular(t *testing.T) {
+	parent := filepath.Join(t.TempDir(), "private")
+	if err := os.Mkdir(parent, 0o700); err != nil {
+		t.Fatal(err)
+	}
+	if err := safeio.ProtectPrivateDirectory(parent); err != nil {
+		t.Fatal(err)
+	}
+	target := filepath.Join(parent, "auth.yaml")
+	if err := replaceRestoreFile(target, []byte("created"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if err := safeio.ValidatePrivateRegular(target); err != nil {
+		t.Fatalf("created restore file is not owner-only: %v", err)
+	}
+	if err := replaceRestoreFile(target, []byte("replacement"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if err := safeio.ValidatePrivateRegular(target); err != nil {
+		t.Fatalf("replacement restore file is not owner-only: %v", err)
+	}
+	contents, err := os.ReadFile(target)
+	if err != nil || string(contents) != "replacement" {
+		t.Fatalf("replacement contents = %q, error = %v", contents, err)
+	}
+}
+
+func TestReplaceRestoreFileWindowsPinsParentAndRejectsReparsePath(t *testing.T) {
+	root := t.TempDir()
+	parent := filepath.Join(root, "private")
+	if err := os.Mkdir(parent, 0o700); err != nil {
+		t.Fatal(err)
+	}
+	if err := safeio.ProtectPrivateDirectory(parent); err != nil {
+		t.Fatal(err)
+	}
+	target := filepath.Join(parent, "users.yaml")
+	if err := os.WriteFile(target, []byte("old"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if err := safeio.ProtectPrivateRegular(target); err != nil {
+		t.Fatal(err)
+	}
+	renamed := parent + "-renamed"
+	var hookCalled bool
+	restoreHook := safeio.SetPrivateDirectoryTestHookForTest(func(stage string) {
+		if stage != "after-restore-parent-open" {
+			return
+		}
+		hookCalled = true
+		if err := os.Rename(parent, renamed); err == nil {
+			t.Fatal("parent rename succeeded while restore retained its directory handles")
+		}
+	})
+	defer restoreHook()
+	if err := replaceRestoreFile(target, []byte("new"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if !hookCalled {
+		t.Fatal("parent-pinning race hook was not reached")
+	}
+
+	link := filepath.Join(root, "reparse-parent")
+	if err := os.Symlink(parent, link); err != nil {
+		t.Skipf("Windows host does not permit symlink creation: %v", err)
+	}
+	if err := replaceRestoreFile(filepath.Join(link, "users.yaml"), []byte("unsafe"), 0o600); !errors.Is(err, safeio.ErrUnsafeFile) {
+		t.Fatalf("reparse-parent restore error = %v, want ErrUnsafeFile", err)
+	}
+}