Add check to not overwrite an existing key when migrating after downg…

…rade (#5709)

## Motivation

Downgrading to v1.3.x after upgrading to v1.4.x will generate a new key that when the node is updated again to v1.4.x will overwrite the existing key.

This adds a check that prevents the node from overwriting a possibly already existing key.

CHANGELOG.md

@@ -2,6 +2,19 @@
 
 See [RELEASE](./RELEASE.md) for workflow instructions.
 
+## UNRELEASED
+
+### Upgrade information
+
+### Highlights
+
+### Features
+
+### Improvements
+
+* [#5709](https://github.com/spacemeshos/go-spacemesh/pull/5709) Prevent users from accidentally deleting their keys,
+  if they downgrade to v1.3.x and upgrade again.
+
 ## Release v1.4.0
 
 ### Upgrade information
@@ -228,9 +241,10 @@ and permanent ineligibility for rewards.
 
 ### Features
 
-* [#5678](https://github.com/spacemeshos/go-spacemesh/pull/5678) API to for changing log level without restarting a node. Examples: 
-  > grpcurl -plaintext -d '{"module": "sync", "level": "debug"}' 127.0.0.1:9093 spacemesh.v1.DebugService.ChangeLogLevel
+* [#5678](https://github.com/spacemeshos/go-spacemesh/pull/5678) API to for changing log level without restarting a
+  node. Examples:
 
+  > grpcurl -plaintext -d '{"module": "sync", "level": "debug"}' 127.0.0.1:9093 spacemesh.v1.DebugService.ChangeLogLevel
   > grpcurl -plaintext -d '{"module": "*", "level": "debug"}' 127.0.0.1:9093 spacemesh.v1.DebugService.ChangeLogLevel
 
   "*" will replace log level for all known modules, expect that some of them will spam too much.

node/node_identities.go

@@ -68,6 +68,28 @@ func (app *App) MigrateExistingIdentity() error {
 		return fmt.Errorf("failed to create directory for identity file: %w", err)
 	}
 
+	_, err = os.Stat(newKey)
+	switch {
+	case errors.Is(err, fs.ErrNotExist):
+		// no new key, migrate old to new
+	case err == nil:
+		// both exist, error
+		return fmt.Errorf("%w: both %s and %s exist", fs.ErrExist, newKey, oldKey)
+	case err != nil:
+		return fmt.Errorf("stat %s: %w", newKey, err)
+	}
+
+	_, err = os.Stat(oldKey + ".bak")
+	switch {
+	case errors.Is(err, fs.ErrNotExist):
+		// no backup, migrate old to new
+	case err == nil:
+		// backup already exists - something is wrong
+		return fmt.Errorf("%w: backup %s already exists", fs.ErrExist, oldKey+".bak")
+	case err != nil:
+		return fmt.Errorf("stat %s: %w", oldKey+".bak", err)
+	}
+
 	dst, err := os.Create(newKey)
 	if err != nil {
 		return fmt.Errorf("failed to create new identity file: %w", err)

node/node_identities_test.go

@@ -213,3 +213,102 @@ func TestSpacemeshApp_LoadIdentities(t *testing.T) {
 		require.Len(t, app.signers, 3)
 	})
 }
+
+func Test_MigrateExistingIdentity(t *testing.T) {
+	t.Run("no key - no migration", func(t *testing.T) {
+		app := New(WithLog(logtest.New(t)))
+		app.Config.DataDirParent = t.TempDir()
+		app.Config.SMESHING.Opts.DataDir = t.TempDir()
+		err := app.MigrateExistingIdentity()
+		require.NoError(t, err)
+	})
+
+	t.Run("existing key is migrated", func(t *testing.T) {
+		app := New(WithLog(logtest.New(t)))
+		app.Config.DataDirParent = t.TempDir()
+		app.Config.SMESHING.Opts.DataDir = t.TempDir()
+
+		sig, err := signing.NewEdSigner()
+		require.NoError(t, err)
+
+		err = os.WriteFile(filepath.Join(app.Config.SMESHING.Opts.DataDir, legacyKeyFileName), sig.PrivateKey(), 0o600)
+		require.NoError(t, err)
+
+		err = app.MigrateExistingIdentity()
+		require.NoError(t, err)
+
+		require.FileExists(t, filepath.Join(app.Config.DataDirParent, keyDir, supervisedIDKeyFileName))
+		require.NoFileExists(t, filepath.Join(app.Config.SMESHING.Opts.DataDir, legacyKeyFileName))
+		require.FileExists(t, filepath.Join(app.Config.SMESHING.Opts.DataDir, legacyKeyFileName+".bak"))
+	})
+
+	t.Run("migration does not overwrite existing key", func(t *testing.T) {
+		app := New(WithLog(logtest.New(t)))
+		app.Config.DataDirParent = t.TempDir()
+		app.Config.SMESHING.Opts.DataDir = t.TempDir()
+
+		sigOld, err := signing.NewEdSigner()
+		require.NoError(t, err)
+
+		oldKey := filepath.Join(app.Config.SMESHING.Opts.DataDir, legacyKeyFileName)
+		err = os.WriteFile(oldKey, sigOld.PrivateKey(), 0o600)
+		require.NoError(t, err)
+
+		sigNew, err := signing.NewEdSigner()
+		require.NoError(t, err)
+
+		newKey := filepath.Join(app.Config.DataDirParent, keyDir, supervisedIDKeyFileName)
+		err = os.MkdirAll(filepath.Dir(newKey), 0o700)
+		require.NoError(t, err)
+		err = os.WriteFile(newKey, sigNew.PrivateKey(), 0o600)
+		require.NoError(t, err)
+
+		err = app.MigrateExistingIdentity()
+		require.ErrorIs(t, err, fs.ErrExist)
+		require.ErrorContains(t, err, fmt.Sprintf("both %s and %s exist", newKey, oldKey))
+		require.FileExists(t, newKey)
+		require.FileExists(t, oldKey)
+
+		newKeyBin, err := os.ReadFile(newKey)
+		require.NoError(t, err)
+		require.Equal(t, []byte(sigNew.PrivateKey()), newKeyBin)
+
+		oldKeyBin, err := os.ReadFile(oldKey)
+		require.NoError(t, err)
+		require.Equal(t, []byte(sigOld.PrivateKey()), oldKeyBin)
+	})
+
+	t.Run("migrate with an already existing backup", func(t *testing.T) {
+		app := New(WithLog(logtest.New(t)))
+		app.Config.DataDirParent = t.TempDir()
+		app.Config.SMESHING.Opts.DataDir = t.TempDir()
+
+		sigOld, err := signing.NewEdSigner()
+		require.NoError(t, err)
+
+		oldKey := filepath.Join(app.Config.SMESHING.Opts.DataDir, legacyKeyFileName)
+		err = os.WriteFile(oldKey, sigOld.PrivateKey(), 0o600)
+		require.NoError(t, err)
+
+		sigBackup, err := signing.NewEdSigner()
+		require.NoError(t, err)
+
+		backupKey := filepath.Join(app.Config.SMESHING.Opts.DataDir, legacyKeyFileName+".bak")
+		err = os.WriteFile(backupKey, sigBackup.PrivateKey(), 0o600)
+		require.NoError(t, err)
+
+		err = app.MigrateExistingIdentity()
+		require.ErrorIs(t, err, fs.ErrExist)
+		require.ErrorContains(t, err, fmt.Sprintf("backup %s already exists", backupKey))
+		require.FileExists(t, filepath.Join(app.Config.SMESHING.Opts.DataDir, legacyKeyFileName))
+		require.FileExists(t, filepath.Join(app.Config.SMESHING.Opts.DataDir, legacyKeyFileName+".bak"))
+
+		oldKeyBin, err := os.ReadFile(oldKey)
+		require.NoError(t, err)
+		require.Equal(t, []byte(sigOld.PrivateKey()), oldKeyBin)
+
+		backupKeyBin, err := os.ReadFile(backupKey)
+		require.NoError(t, err)
+		require.Equal(t, []byte(sigBackup.PrivateKey()), backupKeyBin)
+	})
+}