openvpn: T7633: Add support for 'data-ciphers-fallback' in site-to-site tunnels

- Introduced new CLI option 'data-ciphers-fallback' for OpenVPN interfaces
  (used as fallback cipher in site-to-site mode)
- Adjust migration 1‑to‑2 to skip migrating 'cipher' for site‑to‑site interfaces

3 files changed, 52 insertions, 0 deletions

diff --git a/src/conf_mode/interfaces_openvpn.py b/src/conf_mode/interfaces_openvpn.py
index 5cc09da89..bb9d06389 100755
--- a/src/conf_mode/interfaces_openvpn.py
+++ b/src/conf_mode/interfaces_openvpn.py
@@ -168,6 +168,12 @@ def is_ec_private_key(pki, cert_name):
     key = load_private_key(pki_cert['private']['key'])
     return isinstance(key, ec.EllipticCurvePrivateKey)
 
+
+def verify_data_ciphers_fallback(openvpn):
+    if openvpn['mode'] != 'site-to-site':
+        if dict_search('encryption.data_ciphers_fallback', openvpn):
+            raise ConfigError('Cipher fallback is valid only in site-to-site mode')
+
 def verify_pki(openvpn):
     pki = openvpn['pki']
     interface = openvpn['ifname']
@@ -615,6 +621,8 @@ def verify(openvpn):
     verify_bond_bridge_member(openvpn)
     verify_mirror_redirect(openvpn)
 
+    verify_data_ciphers_fallback(openvpn)
+
     return None
 
 def generate_pki_files(openvpn):
diff --git a/src/migration-scripts/openvpn/1-to-2 b/src/migration-scripts/openvpn/1-to-2
index 83d6219d6..75360446c 100644
--- a/src/migration-scripts/openvpn/1-to-2
+++ b/src/migration-scripts/openvpn/1-to-2
@@ -25,11 +25,17 @@ def migrate(config: ConfigTree) -> None:
         # Remove 'encryption cipher' and add this value to 'encryption ncp-ciphers'
         # for server and client mode.
         # Site-to-site mode still can use --cipher option
+        mode_path = ['interfaces', 'openvpn', i, 'mode']
         cipher_path = ['interfaces', 'openvpn', i, 'encryption', 'cipher']
         ncp_cipher_path = ['interfaces', 'openvpn', i, 'encryption', 'ncp-ciphers']
+
         if config.exists(cipher_path):
             if config.exists(['interfaces', 'openvpn', i, 'shared-secret-key']):
                 continue
+            # Only migrate if mode is not 'site-to-site'
+            if config.value_exists(mode_path, 'site-to-site'):
+                continue
+
             cipher = config.return_value(cipher_path)
             config.delete(cipher_path)
             if cipher == 'none':
diff --git a/src/migration-scripts/openvpn/4-to-5 b/src/migration-scripts/openvpn/4-to-5
new file mode 100644
index 000000000..5c7ee833c
--- /dev/null
+++ b/src/migration-scripts/openvpn/4-to-5
@@ -0,0 +1,38 @@
+#!/usr/bin/env python3
+# Copyright VyOS maintainers and contributors <maintainers@vyos.io>
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this library.  If not, see <http://www.gnu.org/licenses/>.
+#
+# T7633: This migration converts legacy 'encryption cipher' directives into
+# 'encryption data-ciphers-fallback' for site-to-site mode tunnels.
+#
+# In modern OpenVPN (v2.6+), 'cipher' and 'data-ciphers' are not valid
+# in site-to-site mode.
+# The appropriate directive is now '--data-ciphers-fallback alg'.
+
+from vyos.configtree import ConfigTree
+
+def migrate(config: ConfigTree) -> None:
+    ovpn_intfs = config.list_nodes(['interfaces', 'openvpn'], path_must_exist=False)
+    for i in ovpn_intfs:
+        base_path = ['interfaces', 'openvpn', i]
+        mode_path = base_path + ['mode']
+        cipher_path = base_path + ['encryption', 'cipher']
+
+        # Only migrate if mode is explicitly 'site-to-site'
+        if config.value_exists(mode_path, 'site-to-site'):
+
+            # Rename 'encryption cipher' with 'encryption data-ciphers-fallback'
+            if config.exists(cipher_path):
+                config.rename(cipher_path, 'data-ciphers-fallback')