Delete the keychain item or Secure Enclave key of a failed unlocker add (closes #89)

A Secure Enclave unlocker add gets the long-term key before it creates
the Secure Enclave key, so a wrong passphrase creates none, and deletes
the key if a later step fails. macse.CreateKey finds the new key's hash
right after sc_auth creates it, failing with an error naming the label
if it cannot, and deletes the key if getting its public key then fails.
A keychain unlocker add writes all of the unlocker's files before it
stores the keychain item, and deletes the item if moving the unlocker
into place then fails. A failure to delete is reported along with the
original error.

The Objective-C and macse_darwin.go were only read, never compiled or
run; the new tests run only on a Mac.

Model: opus-5-5

internal/macse/macse_darwin.go

@@ -15,6 +15,7 @@ package macse
 import "C"
 
 import (
+	"errors"
 	"fmt"
 	"unsafe"
 )
@@ -39,10 +40,9 @@ const (
 
 // CreateKey creates a new P-256 non-exportable key in the Secure Enclave via sc_auth.
 // Returns the uncompressed public key bytes (65 bytes) and the identity hash
-// (for deletion).
+// (for deletion). If getting the public key fails, CreateKey deletes the key
+// again; a failure to delete is returned along with the first error.
 func CreateKey(label string) (publicKey []byte, hash string, err error) {
-	pubKeyBuf := make([]C.uint8_t, p256UncompressedKeySize)
-	pubKeyLen := C.int(p256UncompressedKeySize)
 	var hashBuf [hashBufferSize]C.char
 	var errBuf [errorBufferSize]C.char
 
@@ -50,7 +50,6 @@ func CreateKey(label string) (publicKey []byte, hash string, err error) {
 	defer C.free(unsafe.Pointer(cLabel)) //nolint:nlreturn // CGo free pattern
 
 	result := C.se_create_key(cLabel,
-		&pubKeyBuf[0], &pubKeyLen,
 		&hashBuf[0], C.int(hashBufferSize),
 		&errBuf[0], C.int(errorBufferSize))
 
@@ -58,9 +57,29 @@ func CreateKey(label string) (publicKey []byte, hash string, err error) {
 		return nil, "", fmt.Errorf("secure enclave: %s", C.GoString(&errBuf[0]))
 	}
 
+	h := C.GoString(&hashBuf[0])
+
+	pubKeyBuf := make([]C.uint8_t, p256UncompressedKeySize)
+	pubKeyLen := C.int(p256UncompressedKeySize)
+
+	result = C.se_copy_public_key(cLabel,
+		&pubKeyBuf[0], &pubKeyLen,
+		&errBuf[0], C.int(errorBufferSize))
+
+	if result != 0 {
+		err = fmt.Errorf("secure enclave: %s", C.GoString(&errBuf[0]))
+
+		deleteErr := DeleteKey(h)
+		if deleteErr != nil {
+			err = errors.Join(err,
+				fmt.Errorf("failed to delete key %s: %w", label, deleteErr))
+		}
+
+		return nil, "", err
+	}
+
 	//nolint:nlreturn // CGo result extraction
 	pk := C.GoBytes(unsafe.Pointer(&pubKeyBuf[0]), pubKeyLen)
-	h := C.GoString(&hashBuf[0])
 
 	return pk, h, nil
 }

internal/macse/secure_enclave.h

@@ -5,20 +5,30 @@
 
 #include <stdint.h>
 
-// se_create_key creates a new P-256 key in the Secure Enclave via sc_auth.
+// se_create_key creates a new P-256 key in the Secure Enclave via sc_auth and
+// finds its identity hash. If the hash cannot be found, the key exists but
+// se_create_key fails, with an error naming the label.
 // label: unique identifier for the CTK identity (UTF-8 C string)
-// pub_key_out: output buffer for the uncompressed public key (65 bytes for P-256)
-// pub_key_len: on input, size of pub_key_out; on output, actual size written
 // hash_out: output buffer for the identity hash (for deletion)
 // hash_out_len: size of hash_out buffer
 // error_out: output buffer for error message
 // error_out_len: size of error_out buffer
 // Returns 0 on success, -1 on failure.
 int se_create_key(const char *label,
-                  uint8_t *pub_key_out, int *pub_key_len,
                   char *hash_out, int hash_out_len,
                   char *error_out, int error_out_len);
 
+// se_copy_public_key copies the public key of a CTK identity.
+// label: label of the CTK identity
+// pub_key_out: output buffer for the uncompressed public key (65 bytes for P-256)
+// pub_key_len: on input, size of pub_key_out; on output, actual size written
+// error_out: output buffer for error message
+// error_out_len: size of error_out buffer
+// Returns 0 on success, -1 on failure.
+int se_copy_public_key(const char *label,
+                       uint8_t *pub_key_out, int *pub_key_len,
+                       char *error_out, int error_out_len);
+
 // se_encrypt encrypts data using the SE-backed public key (ECIES).
 // label: label of the CTK identity whose public key to use
 // plaintext: data to encrypt

internal/macse/secure_enclave.m

@@ -47,7 +47,6 @@ static SecKeyRef lookup_ctk_private_key(const char *label, char *error_out, int
 }
 
 int se_create_key(const char *label,
-                  uint8_t *pub_key_out, int *pub_key_len,
                   char *hash_out, int hash_out_len,
                   char *error_out, int error_out_len) {
     @autoreleasepool {
@@ -87,7 +86,56 @@ int se_create_key(const char *label,
             return -1;
         }
 
-        // Retrieve the public key from the created identity
+        // Get the identity hash, which deleting the key needs, by parsing
+        // sc_auth list output
+        hash_out[0] = '\0';
+        NSTask *listTask = [[NSTask alloc] init];
+        listTask.executableURL = [NSURL fileURLWithPath:@"/usr/sbin/sc_auth"];
+        listTask.arguments = @[@"list-ctk-identities"];
+
+        NSPipe *listPipe = [NSPipe pipe];
+        listTask.standardOutput = listPipe;
+        listTask.standardError = [NSPipe pipe];
+
+        if ([listTask launchAndReturnError:&nsError]) {
+            [listTask waitUntilExit];
+            NSData *listData = [listPipe.fileHandleForReading readDataToEndOfFile];
+            NSString *listStr = [[NSString alloc] initWithData:listData
+                                                      encoding:NSUTF8StringEncoding];
+
+            for (NSString *line in [listStr componentsSeparatedByString:@"\n"]) {
+                if ([line containsString:labelStr]) {
+                    NSMutableArray *tokens = [NSMutableArray array];
+                    for (NSString *part in [line componentsSeparatedByCharactersInSet:
+                                            [NSCharacterSet whitespaceCharacterSet]]) {
+                        if (part.length > 0) {
+                            [tokens addObject:part];
+                        }
+                    }
+                    if (tokens.count > 1) {
+                        snprintf(hash_out, hash_out_len, "%s", [tokens[1] UTF8String]);
+                    }
+                    break;
+                }
+            }
+        }
+
+        if (hash_out[0] == '\0') {
+            NSString *msg = [NSString stringWithFormat:
+                             @"created key '%s' but found no hash for it in sc_auth list-ctk-identities",
+                             label];
+            snprintf_error(error_out, error_out_len, msg);
+            return -1;
+        }
+
+        return 0;
+    }
+}
+
+int se_copy_public_key(const char *label,
+                       uint8_t *pub_key_out, int *pub_key_len,
+                       char *error_out, int error_out_len) {
+    @autoreleasepool {
         SecKeyRef privateKey = lookup_ctk_private_key(label, error_out, error_out_len);
         if (!privateKey) {
             return -1;
@@ -126,39 +174,6 @@ int se_create_key(const char *label,
         *pub_key_len = (int)length;
         CFRelease(pubKeyData);
 
-        // Get the identity hash by parsing sc_auth list output
-        hash_out[0] = '\0';
-        NSTask *listTask = [[NSTask alloc] init];
-        listTask.executableURL = [NSURL fileURLWithPath:@"/usr/sbin/sc_auth"];
-        listTask.arguments = @[@"list-ctk-identities"];
-
-        NSPipe *listPipe = [NSPipe pipe];
-        listTask.standardOutput = listPipe;
-        listTask.standardError = [NSPipe pipe];
-
-        if ([listTask launchAndReturnError:&nsError]) {
-            [listTask waitUntilExit];
-            NSData *listData = [listPipe.fileHandleForReading readDataToEndOfFile];
-            NSString *listStr = [[NSString alloc] initWithData:listData
-                                                      encoding:NSUTF8StringEncoding];
-
-            for (NSString *line in [listStr componentsSeparatedByString:@"\n"]) {
-                if ([line containsString:labelStr]) {
-                    NSMutableArray *tokens = [NSMutableArray array];
-                    for (NSString *part in [line componentsSeparatedByCharactersInSet:
-                                            [NSCharacterSet whitespaceCharacterSet]]) {
-                        if (part.length > 0) {
-                            [tokens addObject:part];
-                        }
-                    }
-                    if (tokens.count > 1) {
-                        snprintf(hash_out, hash_out_len, "%s", [tokens[1] UTF8String]);
-                    }
-                    break;
-                }
-            }
-        }
-
         return 0;
     }
 }

internal/secret/atomic_test.go

@@ -8,6 +8,7 @@ import (
 	"testing"
 
 	"filippo.io/age"
+	"git.eeqj.de/sneak/secret/internal/macse"
 	"git.eeqj.de/sneak/secret/internal/secret"
 	"git.eeqj.de/sneak/secret/internal/vault"
 	"github.com/awnumar/memguard"
@@ -899,3 +900,42 @@ func TestWriteDirRefusesExistingDir(t *testing.T) {
 		})
 	}
 }
+
+// TestSecureEnclaveUnlockerFailureDeletesKey makes moving a new Secure
+// Enclave unlocker into place fail after its Secure Enclave key is created:
+// the key must be deleted again. Skipped when the add fails before that, as
+// it does everywhere but in a macOS build with cgo on a Mac with a Secure
+// Enclave.
+func TestSecureEnclaveUnlockerFailureDeletesKey(t *testing.T) {
+	t.Parallel()
+
+	mnemonic := testMnemonicBuffer(t)
+	base := afero.NewMemMapFs()
+	_, err := vault.CreateVault(base, testVaultStateDir, testVaultName, mnemonic)
+	require.NoError(t, err)
+
+	// The unlocker's directory is named se-<label of its Secure Enclave key>
+	var seKeyLabel string
+
+	fs := hookFs{Fs: base, before: func(op, path string) error {
+		if op == opRename && filepath.Base(filepath.Dir(path)) == "unlockers.d" {
+			seKeyLabel = strings.TrimPrefix(filepath.Base(path), "se-")
+
+			return errInjected
+		}
+
+		return nil
+	}}
+
+	_, err = secret.CreateSecureEnclaveUnlocker(fs, testVaultStateDir, mnemonic,
+		nil)
+
+	if seKeyLabel == "" {
+		t.Skipf("the add failed before moving the unlocker into place: %v", err)
+	}
+
+	require.ErrorIs(t, err, errInjected)
+
+	_, err = macse.Encrypt(seKeyLabel, []byte("test"))
+	assert.Error(t, err, "Secure Enclave key left behind")
+}

internal/secret/keychainunlocker.go

@@ -490,6 +490,8 @@ func CreateKeychainUnlocker(
 
 // writeKeychainUnlocker writes a new keychain unlocker into unlockerDir and
 // stores its data in the keychain (steps 7 and 8 of CreateKeychainUnlocker).
+// The data is stored after the unlocker's files are written, and the keychain
+// item is deleted again if moving the unlocker into place then fails.
 func writeKeychainUnlocker(
 	fs afero.Fs, unlockerDir, keychainItemName, ageRecipient string,
 	encryptedAgePrivKey, encryptedLtPrivKey []byte,
@@ -510,8 +512,10 @@ func writeKeychainUnlocker(
 		return nil, fmt.Errorf("failed to marshal unlocker metadata: %w", err)
 	}
 
-	// Step 8: Write the unlocker's files and store the data in the keychain,
-	// the metadata last
+	// Step 8: Write the unlocker's files, the metadata last, then store the
+	// data in the keychain
+	stored := false
+
 	err = WriteDir(fs, unlockerDir, func(dir string) error {
 		err := WriteFileAtomic(fs, filepath.Join(dir, "pub.txt"), []byte(ageRecipient))
 		if err != nil {
@@ -528,19 +532,29 @@ func writeKeychainUnlocker(
 			return fmt.Errorf("failed to write encrypted long-term private key: %w", err)
 		}
 
-		err = storeInKeychain(keychainItemName, keychainDataBuffer)
-		if err != nil {
-			return fmt.Errorf("failed to store data in keychain: %w", err)
-		}
-
 		err = WriteFileAtomic(fs, filepath.Join(dir, "unlocker-metadata.json"),
 			metadataBytes)
 		if err != nil {
 			return fmt.Errorf("failed to write unlocker metadata: %w", err)
 		}
 
+		err = storeInKeychain(keychainItemName, keychainDataBuffer)
+		if err != nil {
+			return fmt.Errorf("failed to store data in keychain: %w", err)
+		}
+
+		stored = true
+
 		return nil
 	})
+	if err != nil && stored {
+		deleteErr := deleteFromKeychain(keychainItemName)
+		if deleteErr != nil {
+			err = errors.Join(err, fmt.Errorf(
+				"failed to delete keychain item %s: %w", keychainItemName, deleteErr))
+		}
+	}
+
 	if err != nil {
 		return nil, err
 	}

internal/secret/keychainunlocker_test.go

@@ -4,10 +4,13 @@ package secret
 
 import (
 	"encoding/hex"
+	"os"
+	"path/filepath"
 	"runtime"
 	"testing"
 
 	"github.com/awnumar/memguard"
+	"github.com/spf13/afero"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -185,3 +188,27 @@ func TestDeleteNonExistentKeychainItem(t *testing.T) {
 	assert.NoError(t, err,
 		"Deleting non-existent keychain item should not return an error")
 }
+
+// TestWriteKeychainUnlockerFailureDeletesItem makes moving a new keychain
+// unlocker into place fail after its data is stored in the keychain: the
+// keychain item must be deleted again.
+func TestWriteKeychainUnlockerFailureDeletesItem(t *testing.T) {
+	testItemName := "test-secret-keychain-unlocker-cleanup"
+	_ = deleteFromKeychain(testItemName)
+
+	// Moving the unlocker into a read-only directory fails
+	unlockersDir := filepath.Join(t.TempDir(), "unlockers.d")
+	require.NoError(t, os.Mkdir(unlockersDir, 0o500))
+
+	testBuffer := memguard.NewBufferFromBytes([]byte("test-keychain-data"))
+	defer testBuffer.Destroy()
+
+	_, err := writeKeychainUnlocker(afero.NewOsFs(),
+		filepath.Join(unlockersDir, testItemName), testItemName, "age1test",
+		[]byte("test-priv"), []byte("test-longterm"), testBuffer)
+	require.ErrorIs(t, err, os.ErrPermission,
+		"moving the unlocker into place should fail")
+
+	_, err = retrieveFromKeychain(testItemName)
+	assert.Error(t, err, "keychain item left behind")
+}

internal/secret/seunlocker_darwin.go

@@ -4,6 +4,7 @@ package secret
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"log/slog"
 	"os"
@@ -216,6 +217,8 @@ func generateSEKeyLabel(vaultName string) (string, error) {
 // using ECIES. No intermediate age keypair is used.
 // The long-term key comes from mnemonic when it is not nil, else from the
 // current unlocker, as getLongTermKeyForSE describes.
+// The SE key is created once the long-term key is in hand and the unlocker's
+// path is known, and is deleted again if a later step fails.
 func CreateSecureEnclaveUnlocker(
 	fs afero.Fs,
 	stateDir string,
@@ -237,17 +240,7 @@ func CreateSecureEnclaveUnlocker(
 		return nil, fmt.Errorf("failed to generate SE key label: %w", err)
 	}
 
-	// Step 1: Create P-256 key in the Secure Enclave via sc_auth
-	Debug("Creating Secure Enclave key", "label", seKeyLabel)
-
-	_, seKeyHash, err := macse.CreateKey(seKeyLabel)
-	if err != nil {
-		return nil, fmt.Errorf("failed to create SE key: %w", err)
-	}
-
-	Debug("Created SE key", "label", seKeyLabel, "hash", seKeyHash)
-
-	// Step 2: Get the vault's long-term private key
+	// Step 1: Get the vault's long-term private key
 	ltPrivKeyData, err := getLongTermKeyForSE(fs, vault, mnemonic, passphrase)
 	if err != nil {
 		return nil, fmt.Errorf(
@@ -257,16 +250,7 @@ func CreateSecureEnclaveUnlocker(
 	}
 	defer ltPrivKeyData.Destroy()
 
-	// Step 3: Encrypt the long-term key directly with the SE (ECIES)
-	encryptedLtKey, err := macse.Encrypt(seKeyLabel, ltPrivKeyData.Bytes())
-	if err != nil {
-		return nil, fmt.Errorf(
-			"failed to encrypt long-term key with SE: %w",
-			err,
-		)
-	}
-
-	// Step 4: Prepare the unlocker directory's path and metadata
+	// Step 2: Prepare the unlocker directory's path
 	vaultDir, err := vault.GetDirectory()
 	if err != nil {
 		return nil, fmt.Errorf("failed to get vault directory: %w", err)
@@ -275,6 +259,49 @@ func CreateSecureEnclaveUnlocker(
 	unlockerDirName := "se-" + filepath.Base(seKeyLabel)
 	unlockerDir := filepath.Join(vaultDir, "unlockers.d", unlockerDirName)
 
+	// Step 3: Create P-256 key in the Secure Enclave via sc_auth
+	Debug("Creating Secure Enclave key", "label", seKeyLabel)
+
+	_, seKeyHash, err := macse.CreateKey(seKeyLabel)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create SE key: %w", err)
+	}
+
+	Debug("Created SE key", "label", seKeyLabel, "hash", seKeyHash)
+
+	// Steps 4 and 5: Write the unlocker, or delete the SE key if that fails
+	unlocker, err := writeSEUnlocker(fs, unlockerDir, seKeyLabel, seKeyHash,
+		ltPrivKeyData)
+	if err != nil {
+		deleteErr := macse.DeleteKey(seKeyHash)
+		if deleteErr != nil {
+			err = errors.Join(err, fmt.Errorf(
+				"failed to delete SE key %s: %w", seKeyLabel, deleteErr))
+		}
+
+		return nil, err
+	}
+
+	return unlocker, nil
+}
+
+// writeSEUnlocker encrypts the long-term key with the SE key and writes the
+// new unlocker into unlockerDir (steps 4 and 5 of
+// CreateSecureEnclaveUnlocker).
+func writeSEUnlocker(
+	fs afero.Fs, unlockerDir, seKeyLabel, seKeyHash string,
+	ltPrivKeyData *memguard.LockedBuffer,
+) (*SecureEnclaveUnlocker, error) {
+	// Step 4: Encrypt the long-term key directly with the SE (ECIES), and
+	// prepare the metadata
+	encryptedLtKey, err := macse.Encrypt(seKeyLabel, ltPrivKeyData.Bytes())
+	if err != nil {
+		return nil, fmt.Errorf(
+			"failed to encrypt long-term key with SE: %w",
+			err,
+		)
+	}
+
 	seMetadata := SecureEnclaveUnlockerMetadata{
 		UnlockerMetadata: UnlockerMetadata{
 			Type:      seUnlockerType,