fix: run DWH verification with read-only registry access

tools/dwh-auth/internal/registry/store.go

@@ -47,6 +47,8 @@ var (
 	ErrConflict = errors.New("credential record already exists")
 	// ErrIntegrity means an unsafe or malformed registry object was observed.
 	ErrIntegrity = errors.New("registry integrity failure")
+	// ErrReadOnly means a runtime reader was asked to mutate registry state.
+	ErrReadOnly = errors.New("registry is read-only")
 )
 
 // PublicRecord is the redacted inventory form of a persisted record.
@@ -64,11 +66,12 @@ type PublicRecord struct {
 
 // Store owns protected descriptors for one registry root.
 type Store struct {
-	mu      sync.RWMutex
-	now     func() time.Time
-	root    *securefile.Dir
-	active  *securefile.Dir
-	revoked *securefile.Dir
+	mu       sync.RWMutex
+	now      func() time.Time
+	root     *securefile.Dir
+	active   *securefile.Dir
+	revoked  *securefile.Dir
+	readOnly bool
 }
 
 type storedRecord struct {
@@ -94,9 +97,56 @@ func Open(root string) (*Store, error) {
 		_ = rootDir.Close()
 		return nil, integrity(err)
 	}
+	lock, err := rootDir.Lock(registryLockName)
+	if err != nil {
+		_ = revoked.Close()
+		_ = active.Close()
+		_ = rootDir.Close()
+		return nil, integrity(err)
+	}
+	if err := lock.Close(); err != nil {
+		_ = revoked.Close()
+		_ = active.Close()
+		_ = rootDir.Close()
+		return nil, integrity(err)
+	}
 	return &Store{root: rootDir, active: active, revoked: revoked, now: time.Now}, nil
 }
 
+// OpenReadOnly opens only a complete preprovisioned protected registry. It
+// neither creates registry paths nor permits mutations through the Store.
+func OpenReadOnly(root string) (*Store, error) {
+	rootDir, err := securefile.OpenDir(root)
+	if err != nil {
+		return nil, integrity(err)
+	}
+	active, err := rootDir.OpenDir(string(StateActive))
+	if err != nil {
+		_ = rootDir.Close()
+		return nil, integrity(err)
+	}
+	revoked, err := rootDir.OpenDir(string(StateRevoked))
+	if err != nil {
+		_ = active.Close()
+		_ = rootDir.Close()
+		return nil, integrity(err)
+	}
+	lock, err := rootDir.LockShared(registryLockName)
+	if err != nil {
+		_ = revoked.Close()
+		_ = active.Close()
+		_ = rootDir.Close()
+		return nil, integrity(err)
+	}
+	if err := lock.Close(); err != nil {
+		_ = revoked.Close()
+		_ = active.Close()
+		_ = rootDir.Close()
+		return nil, integrity(err)
+	}
+	return &Store{root: rootDir, active: active, revoked: revoked, now: time.Now, readOnly: true}, nil
+}
+
 // Close closes descriptors held by the store.
 func (s *Store) Close() error {
 	if s == nil {
@@ -119,6 +169,9 @@ func (s *Store) Close() error {
 // Add validates and atomically publishes one active record. Existing active or
 // revoked records cannot be overwritten or resurrected.
 func (s *Store) Add(value record.Record) error {
+	if s != nil && s.readOnly {
+		return ErrReadOnly
+	}
 	if err := validateForState(value, StateActive); err != nil {
 		return err
 	}
@@ -261,6 +314,9 @@ func (s *Store) listUnlocked() ([]PublicRecord, error) {
 // Revoke publishes a validated revoked record and fsyncs it before removing the
 // active record. If deletion then fails, Find still returns ErrRevoked.
 func (s *Store) Revoke(keyID, reason string, at time.Time) error {
+	if s != nil && s.readOnly {
+		return ErrReadOnly
+	}
 	if !validKeyID(keyID) {
 		return ErrNotFound
 	}

tools/dwh-auth/internal/registry/store_test.go

@@ -112,6 +112,82 @@ func TestOpenRejectsSymlinkedRegistryRootAndDirectories(t *testing.T) {
 	})
 }
 
+func TestOpenReadOnlyRequiresCompletePreprovisionedRegistryAndNeverCreates(t *testing.T) {
+	root := t.TempDir()
+	before, err := os.ReadDir(root)
+	if err != nil {
+		t.Fatalf("ReadDir(before) error = %v", err)
+	}
+	if _, err := OpenReadOnly(root); err == nil {
+		t.Fatal("OpenReadOnly(incomplete) error = nil, want refusal")
+	}
+	after, err := os.ReadDir(root)
+	if err != nil {
+		t.Fatalf("ReadDir(after) error = %v", err)
+	}
+	if !reflect.DeepEqual(before, after) {
+		t.Fatalf("OpenReadOnly(incomplete) changed root entries: before=%v after=%v", before, after)
+	}
+
+	admin := openStore(t, root)
+	item := syntheticRecord(13)
+	if err := admin.Add(item); err != nil {
+		t.Fatalf("Add() error = %v", err)
+	}
+	if err := admin.Close(); err != nil {
+		t.Fatalf("Close(admin) error = %v", err)
+	}
+	for _, path := range []string{root, filepath.Join(root, "active"), filepath.Join(root, "revoked")} {
+		if err := os.Chmod(path, 0o750|os.ModeSetgid); err != nil {
+			t.Fatalf("Chmod(%q, 2750) error = %v", path, err)
+		}
+	}
+	if info, err := os.Stat(filepath.Join(root, registryLockName)); err != nil || info.Mode().Perm() != 0o640 {
+		t.Fatalf("registry lock = (%v, %v), want 0640", info, err)
+	}
+	entriesBefore := registryEntryModes(t, root)
+	reader, err := OpenReadOnly(root)
+	if err != nil {
+		t.Fatalf("OpenReadOnly() error = %v", err)
+	}
+	defer reader.Close()
+	if found, err := reader.Find(item.KeyID); err != nil || found.KeyID != item.KeyID {
+		t.Fatalf("Find() = (%#v, %v), want protected record", found, err)
+	}
+	if err := reader.Check(); err != nil {
+		t.Fatalf("Check() error = %v", err)
+	}
+	if err := reader.Add(syntheticRecord(14)); err == nil {
+		t.Fatal("read-only Add() error = nil, want refusal")
+	}
+	if err := reader.Revoke(item.KeyID, "synthetic", item.CreatedAt.Add(time.Hour)); err == nil {
+		t.Fatal("read-only Revoke() error = nil, want refusal")
+	}
+	if got := registryEntryModes(t, root); !reflect.DeepEqual(got, entriesBefore) {
+		t.Fatalf("read-only operations changed registry entries: before=%v after=%v", entriesBefore, got)
+	}
+}
+
+func registryEntryModes(t *testing.T, root string) []string {
+	t.Helper()
+	var result []string
+	for _, directory := range []string{root, filepath.Join(root, "active"), filepath.Join(root, "revoked")} {
+		entries, err := os.ReadDir(directory)
+		if err != nil {
+			t.Fatalf("ReadDir(%q) error = %v", directory, err)
+		}
+		for _, entry := range entries {
+			info, err := entry.Info()
+			if err != nil {
+				t.Fatalf("Info(%q) error = %v", entry.Name(), err)
+			}
+			result = append(result, filepath.Join(directory, entry.Name())+":"+info.Mode().String())
+		}
+	}
+	sort.Strings(result)
+	return result
+}
+
 func TestCheckRejectsUnsafeModesAndSymlinkedRecords(t *testing.T) {
 	t.Run("unsafe active mode", func(t *testing.T) {
 		root := t.TempDir()

tools/dwh-auth/internal/securefile/securefile_linux.go

@@ -288,16 +288,38 @@ func (d *Dir) Names() ([]string, error) {
 	return names, nil
 }
 
-// Lock opens or creates a protected 0600 lock file and acquires an exclusive
+// Lock opens or creates a protected 0640 lock file and acquires an exclusive
 // advisory lock. Close releases the lock and descriptor.
 func (d *Dir) Lock(name string) (*Lock, error) {
 	return d.lock(name, syscall.LOCK_EX)
 }
 
-// LockShared opens or creates a protected 0600 lock file and acquires a shared
-// advisory lock. Close releases the lock and descriptor.
+// LockShared opens an existing protected 0640 lock read-only and acquires a
+// shared advisory lock. It never creates or changes registry state.
 func (d *Dir) LockShared(name string) (*Lock, error) {
-	return d.lock(name, syscall.LOCK_SH)
+	if err := validName(name); err != nil {
+		return nil, err
+	}
+	if err := d.check(); err != nil {
+		return nil, err
+	}
+	fd, err := syscall.Openat(d.fd, name, syscall.O_RDONLY|syscall.O_NOFOLLOW|syscall.O_CLOEXEC, 0)
+	if err != nil {
+		return nil, err
+	}
+	if err := validateRegularFD(fd, 0o640); err != nil {
+		_ = syscall.Close(fd)
+		return nil, err
+	}
+	if err := compareWithLstat(fd, filepath.Join(d.path, name), false); err != nil {
+		_ = syscall.Close(fd)
+		return nil, err
+	}
+	if err := syscall.Flock(fd, syscall.LOCK_SH); err != nil {
+		_ = syscall.Close(fd)
+		return nil, err
+	}
+	return &Lock{fd: fd}, nil
 }
 
 func (d *Dir) lock(name string, lockMode int) (*Lock, error) {
@@ -310,14 +332,14 @@ func (d *Dir) lock(name string, lockMode int) (*Lock, error) {
 	for {
 		fd, err := syscall.Openat(d.fd, name, syscall.O_RDWR|syscall.O_NOFOLLOW|syscall.O_CLOEXEC, 0)
 		if errors.Is(err, syscall.ENOENT) {
-			fd, err = syscall.Openat(d.fd, name, syscall.O_RDWR|syscall.O_CREAT|syscall.O_EXCL|syscall.O_NOFOLLOW|syscall.O_CLOEXEC, 0o600)
+			fd, err = syscall.Openat(d.fd, name, syscall.O_RDWR|syscall.O_CREAT|syscall.O_EXCL|syscall.O_NOFOLLOW|syscall.O_CLOEXEC, 0o640)
 			if errors.Is(err, syscall.EEXIST) {
 				continue
 			}
 			if err != nil {
 				return nil, err
 			}
-			if err := syscall.Fchmod(fd, 0o600); err != nil {
+			if err := syscall.Fchmod(fd, 0o640); err != nil {
 				_ = syscall.Close(fd)
 				return nil, err
 			}
@@ -329,7 +351,7 @@ func (d *Dir) lock(name string, lockMode int) (*Lock, error) {
 		if err != nil {
 			return nil, err
 		}
-		if err := validateRegularFD(fd, 0o600); err != nil {
+		if err := validateRegularFD(fd, 0o640); err != nil {
 			_ = syscall.Close(fd)
 			return nil, err
 		}
@@ -495,7 +517,7 @@ func validateDirectoryFD(fd int) error {
 	if stat.Mode&syscall.S_IFMT != syscall.S_IFDIR {
 		return fmt.Errorf("%w: not a directory", ErrUnsafe)
 	}
-	if stat.Mode&0o7022 != 0 {
+	if stat.Mode&0o5022 != 0 {
 		return fmt.Errorf("%w: unsafe directory mode %04o", ErrUnsafe, stat.Mode&0o7777)
 	}
 	return nil

tools/dwh-auth/internal/securefile/securefile_linux_test.go

@@ -93,6 +93,33 @@ func TestProtectedPathsRejectSymlinks(t *testing.T) {
 }
 
 func TestProtectedPathsRejectUnsafeModes(t *testing.T) {
+	t.Run("setgid protected directories", func(t *testing.T) {
+		root := t.TempDir()
+		if err := os.Chmod(root, 0o750|os.ModeSetgid); err != nil {
+			t.Fatalf("Chmod(root) error = %v", err)
+		}
+		dir, err := OpenDir(root)
+		if err != nil {
+			t.Fatalf("OpenDir(2750 root) error = %v", err)
+		}
+		t.Cleanup(func() { _ = dir.Close() })
+		for _, mode := range []os.FileMode{
+			0o750 | os.ModeSetuid,
+			0o750 | os.ModeSetgid | os.ModeSetuid,
+			0o750 | os.ModeSticky,
+			0o770 | os.ModeSetgid,
+			0o752 | os.ModeSetgid,
+		} {
+			path := t.TempDir()
+			if err := os.Chmod(path, mode); err != nil {
+				t.Fatalf("Chmod(%v) error = %v", mode, err)
+			}
+			if _, err := OpenDir(path); err == nil {
+				t.Fatalf("OpenDir(%v) error = nil, want unsafe-mode refusal", mode)
+			}
+		}
+	})
+
 	t.Run("root", func(t *testing.T) {
 		root := t.TempDir()
 		if err := os.Chmod(root, 0o770); err != nil {
@@ -238,6 +265,22 @@ func TestLockSharedAllowsReadersAndBlocksExclusiveWriter(t *testing.T) {
 		t.Fatal("Dir lacks shared advisory locking")
 	}
 
+	if _, err := firstLocker.LockShared("registry.lock"); err == nil {
+		t.Fatal("LockShared(missing) error = nil, want preprovisioned-lock refusal")
+	}
+	if _, err := os.Lstat(filepath.Join(root, "registry.lock")); !errors.Is(err, os.ErrNotExist) {
+		t.Fatalf("LockShared(missing) created lock: %v", err)
+	}
+	bootstrap, err := third.Lock("registry.lock")
+	if err != nil {
+		t.Fatalf("Lock(bootstrap) error = %v", err)
+	}
+	if err := bootstrap.Close(); err != nil {
+		t.Fatalf("Close(bootstrap) error = %v", err)
+	}
+	if info, err := os.Stat(filepath.Join(root, "registry.lock")); err != nil || info.Mode().Perm() != 0o640 {
+		t.Fatalf("bootstrapped lock mode = (%v, %v), want 0640", info, err)
+	}
 	firstShared, err := firstLocker.LockShared("registry.lock")
 	if err != nil {
 		t.Fatalf("LockShared(first) error = %v", err)

tools/dwh-auth/internal/service/service.go

@@ -48,6 +48,18 @@ var socketOwner = func(path string) (uint32, error) {
 	return stat.Uid, nil
 }
 
+var socketParentOwner = func(path string) (uint32, error) {
+	info, err := os.Lstat(path)
+	if err != nil {
+		return 0, err
+	}
+	stat, ok := info.Sys().(*syscall.Stat_t)
+	if !ok {
+		return 0, fmt.Errorf("socket parent owner is unavailable")
+	}
+	return stat.Uid, nil
+}
+
 // New returns the HTTP verifier. It has no network listener and is safe to use
 // with an httptest server only for synthetic test registries.
 func New(store *registry.Store, logger *log.Logger, now func() time.Time) http.Handler {
@@ -101,7 +113,7 @@ func ListenAndServe(ctx context.Context, config Config) error {
 	if err := validateSocketParent(config.Socket); err != nil {
 		return err
 	}
-	store, err := registry.Open(config.RegistryRoot)
+	store, err := registry.OpenReadOnly(config.RegistryRoot)
 	if err != nil {
 		return err
 	}
@@ -164,6 +176,20 @@ func validateSocketParent(socket string) error {
 	if !info.IsDir() || info.Mode()&os.ModeSymlink != 0 {
 		return errors.New("socket parent is not a directory")
 	}
+	if info.Mode().Perm()&0o022 != 0 {
+		return errors.New("socket parent is group or world writable")
+	}
+	stat, ok := info.Sys().(*syscall.Stat_t)
+	if !ok {
+		return errors.New("socket parent owner is unavailable")
+	}
+	owner, err := socketParentOwner(parent)
+	if err != nil {
+		return err
+	}
+	if stat.Uid != uint32(os.Geteuid()) || owner != stat.Uid {
+		return errors.New("socket parent owner mismatch")
+	}
 	resolved, err := filepath.EvalSymlinks(parent)
 	if err != nil || resolved != parent {
 		return errors.New("socket parent is not canonical")

tools/dwh-auth/internal/service/service_test.go

@@ -212,6 +212,7 @@ func TestVerifyMapsMultipleLegacyRecordsToServiceUnavailable(t *testing.T) {
 
 func TestListenAndServeFailsClosedForInvalidPathsAndCollisions(t *testing.T) {
 	root := t.TempDir()
+	initializeRegistry(t, root)
 	parent := t.TempDir()
 	for _, tc := range []struct {
 		name, registryRoot, socket string
@@ -252,8 +253,47 @@ func TestListenAndServeFailsClosedForInvalidPathsAndCollisions(t *testing.T) {
 	}
 }
 
+func TestListenAndServeRejectsUnsafeSocketParents(t *testing.T) {
+	root := t.TempDir()
+	initializeRegistry(t, root)
+	for _, mode := range []os.FileMode{0o770, 0o702} {
+		t.Run("mode "+mode.String(), func(t *testing.T) {
+			parent := t.TempDir()
+			if err := os.Chmod(parent, mode); err != nil {
+				t.Fatalf("Chmod(%v) error = %v", mode, err)
+			}
+			socket := filepath.Join(parent, "verify.sock")
+			err := ListenAndServe(context.Background(), Config{RegistryRoot: root, Socket: socket, Logger: log.New(&bytes.Buffer{}, "", 0), Now: time.Now})
+			if err == nil {
+				t.Fatalf("ListenAndServe(parent mode %v) error = nil, want refusal", mode)
+			}
+			if _, err := os.Lstat(socket); !errors.Is(err, os.ErrNotExist) {
+				t.Fatalf("unsafe parent created socket: %v", err)
+			}
+		})
+	}
+}
+
+func TestListenAndServeRejectsForeignOwnedSocketParent(t *testing.T) {
+	root := t.TempDir()
+	initializeRegistry(t, root)
+	parent := t.TempDir()
+	socket := filepath.Join(parent, "verify.sock")
+	previous := socketParentOwner
+	t.Cleanup(func() { socketParentOwner = previous })
+	socketParentOwner = func(string) (uint32, error) { return uint32(os.Geteuid()) + 1, nil }
+	err := ListenAndServe(context.Background(), Config{RegistryRoot: root, Socket: socket, Logger: log.New(&bytes.Buffer{}, "", 0), Now: time.Now})
+	if err == nil {
+		t.Fatal("ListenAndServe() error = nil, want foreign-parent refusal")
+	}
+	if _, err := os.Lstat(socket); !errors.Is(err, os.ErrNotExist) {
+		t.Fatalf("foreign parent created socket: %v", err)
+	}
+}
+
 func TestListenAndServeReclaimsOnlyOwnedStaleSocketAndCleansUpOnCancellation(t *testing.T) {
 	root := t.TempDir()
+	initializeRegistry(t, root)
 	socket := filepath.Join(t.TempDir(), "verify.sock")
 	stale, err := net.ListenUnix("unix", &net.UnixAddr{Name: socket, Net: "unix"})
 	if err != nil {
@@ -290,6 +330,7 @@ func TestListenAndServeReclaimsOnlyOwnedStaleSocketAndCleansUpOnCancellation(t *
 
 func TestListenAndServeRefusesStaleSocketWithForeignOwner(t *testing.T) {
 	root := t.TempDir()
+	initializeRegistry(t, root)
 	socket := filepath.Join(t.TempDir(), "verify.sock")
 	stale, err := net.ListenUnix("unix", &net.UnixAddr{Name: socket, Net: "unix"})
 	if err != nil {
@@ -313,6 +354,7 @@ func TestListenAndServeRefusesStaleSocketWithForeignOwner(t *testing.T) {
 
 func TestListenAndServeRefusesLiveSocket(t *testing.T) {
 	root := t.TempDir()
+	initializeRegistry(t, root)
 	socket := filepath.Join(t.TempDir(), "verify.sock")
 	live, err := net.ListenUnix("unix", &net.UnixAddr{Name: socket, Net: "unix"})
 	if err != nil {
@@ -330,6 +372,7 @@ func TestListenAndServeRefusesLiveSocket(t *testing.T) {
 
 func TestListenAndServeCleanupRefusesChangedSocketPath(t *testing.T) {
 	root := t.TempDir()
+	initializeRegistry(t, root)
 	socket := filepath.Join(t.TempDir(), "verify.sock")
 	ctx, cancel := context.WithCancel(context.Background())
 	errs := make(chan error, 1)
@@ -363,6 +406,17 @@ func TestListenAndServeCleanupRefusesChangedSocketPath(t *testing.T) {
 	}
 }
 
+func initializeRegistry(t *testing.T, root string) {
+	t.Helper()
+	store, err := registry.Open(root)
+	if err != nil {
+		t.Fatalf("Open() error = %v", err)
+	}
+	if err := store.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+}
+
 func waitForReadySocket(t *testing.T, socket string) {
 	t.Helper()
 	deadline := time.Now().Add(2 * time.Second)