rbd: read configuration from the configmap

if the kms encryption configmap is not mounted
as a volume to the CSI pods, add the code to
read the configuration from the kubernetes. Later
the code to fetch the configmap will be moved to
the new sidecar which is will talk to respective
CO to fetch the encryption configurations.

The k8s configmap uses the standard vault spefic
names to add the configurations. this will be converted
back to the CSI configurations.

Signed-off-by: Madhu Rajanna <madhupr007@gmail.com>

internal/util/crypto.go

@@ -23,6 +23,7 @@ import (
 	"errors"
 	"fmt"
 	"io/ioutil"
+	"os"
 	"path"
 	"strings"
 
@@ -46,6 +47,14 @@ const (
 	// Passphrase size - 20 bytes is 160 bits to satisfy:
 	// https://tools.ietf.org/html/rfc6749#section-10.10
 	encryptionPassphraseSize = 20
+	// podNamespace ENV should be set in the cephcsi container
+	podNamespace = "POD_NAMESPACE"
+
+	// kmsConfigMapName env to read a ConfigMap by name
+	kmsConfigMapName = "KMS_CONFIGMAP_NAME"
+
+	// defaultConfigMapToRead default ConfigMap name to fetch kms connection details
+	defaultConfigMapToRead = "csi-kms-connection-details"
 )
 
 // EncryptionKMS provides external Key Management System for encryption
@@ -113,18 +122,34 @@ func GetKMS(tenant, kmsID string, secrets map[string]string) (EncryptionKMS, err
 	if kmsID == "" || kmsID == defaultKMSType {
 		return initSecretsKMS(secrets)
 	}
-
+	var config map[string]interface{}
 	// #nosec
 	content, err := ioutil.ReadFile(kmsConfigPath)
 	if err != nil {
-		return nil, fmt.Errorf("failed to read kms configuration from %s: %s",
-			kmsConfigPath, err)
+		if !os.IsNotExist(err) {
+			return nil, fmt.Errorf("failed to read kms configuration from %s: %w",
+				kmsConfigPath, err)
+		}
+		// If the configmap is not mounted to the CSI pods read the configmap
+		// the kubernetes.
+		namespace := os.Getenv(podNamespace)
+		if namespace != "" {
+			return nil, fmt.Errorf("%q is not set", podNamespace)
+		}
+		name := os.Getenv(kmsConfigMapName)
+		if name != "" {
+			name = defaultConfigMapToRead
+		}
+		config, err = getVaultConfiguration(namespace, name)
+		if err != nil {
+			return nil, fmt.Errorf("failed to read kms configuration from configmap %s in namespace %s: %w",
+				namespace, name, err)
+		}
 	}
 
-	var config map[string]interface{}
 	err = json.Unmarshal(content, &config)
 	if err != nil {
-		return nil, fmt.Errorf("failed to parse kms configuration: %s", err)
+		return nil, fmt.Errorf("failed to parse kms configuration: %w", err)
 	}
 
 	kmsConfig, ok := config[kmsID].(map[string]interface{})