crypto: use consistent error reporting pattern for unsupported cipher modes

Not all paths in qcrypto_cipher_ctx_new() were correctly distinguishing
between valid user input for cipher mode (which should report a user
facing error), vs program logic errors (which should assert).

Reported-by: Peter Maydell <[email protected]>
Signed-off-by: Daniel P. Berrangé <[email protected]>

Author: berrange

crypto/cipher-nettle.c.inc

@@ -525,8 +525,10 @@ static QCryptoCipher *qcrypto_cipher_ctx_new(QCryptoCipherAlgorithm alg,
             case QCRYPTO_CIPHER_MODE_CTR:
                 drv = &qcrypto_nettle_des_driver_ctr;
                 break;
-            default:
+            case QCRYPTO_CIPHER_MODE_XTS:
                 goto bad_cipher_mode;
+            default:
+                g_assert_not_reached();
             }
 
             ctx = g_new0(QCryptoNettleDES, 1);
@@ -551,8 +553,10 @@ static QCryptoCipher *qcrypto_cipher_ctx_new(QCryptoCipherAlgorithm alg,
             case QCRYPTO_CIPHER_MODE_CTR:
                 drv = &qcrypto_nettle_des3_driver_ctr;
                 break;
-            default:
+            case QCRYPTO_CIPHER_MODE_XTS:
                 goto bad_cipher_mode;
+            default:
+                g_assert_not_reached();
             }
 
             ctx = g_new0(QCryptoNettleDES3, 1);
@@ -663,8 +667,10 @@ static QCryptoCipher *qcrypto_cipher_ctx_new(QCryptoCipherAlgorithm alg,
             case QCRYPTO_CIPHER_MODE_CTR:
                 drv = &qcrypto_nettle_cast128_driver_ctr;
                 break;
-            default:
+            case QCRYPTO_CIPHER_MODE_XTS:
                 goto bad_cipher_mode;
+            default:
+                g_assert_not_reached();
             }
 
             ctx = g_new0(QCryptoNettleCAST128, 1);
@@ -741,8 +747,12 @@ static QCryptoCipher *qcrypto_cipher_ctx_new(QCryptoCipherAlgorithm alg,
             case QCRYPTO_CIPHER_MODE_ECB:
                 drv = &qcrypto_nettle_sm4_driver_ecb;
                 break;
-            default:
+            case QCRYPTO_CIPHER_MODE_CBC:
+            case QCRYPTO_CIPHER_MODE_CTR:
+            case QCRYPTO_CIPHER_MODE_XTS:
                 goto bad_cipher_mode;
+            default:
+                g_assert_not_reached();
             }
 
             ctx = g_new0(QCryptoNettleSm4, 1);