srv6: T591: enable SR enabled packet processing on defined interfaces

The Linux Kernel needs to be told if IPv6 SR enabled packets whether should be
processed or not. This is done using

/proc/sys/net/conf/<iface>/seg6_* variables:

seg6_enabled - BOOL
  Accept or drop SR-enabled IPv6 packets on this interface.
  Relevant packets are those with SRH present and DA = local.
  0 - disabled (default)
  not 0 - enabled

Or the VyOS CLI command:
* set protocols segment-routing interface eth0 srv6

2 files changed, 58 insertions, 11 deletions

diff --git a/src/conf_mode/protocols_segment_routing.py b/src/conf_mode/protocols_segment_routing.py
index eb1653212..d865c2ac0 100755
--- a/src/conf_mode/protocols_segment_routing.py
+++ b/src/conf_mode/protocols_segment_routing.py
@@ -19,7 +19,10 @@ import os
 from sys import exit
 
 from vyos.config import Config
+from vyos.configdict import node_changed
 from vyos.template import render_to_string
+from vyos.utils.dict import dict_search
+from vyos.utils.system import sysctl_write
 from vyos import ConfigError
 from vyos import frr
 from vyos import airbag
@@ -32,33 +35,74 @@ def get_config(config=None):
         conf = Config()
 
     base = ['protocols', 'segment-routing']
-    sr = conf.get_config_dict(base, key_mangling=('-', '_'), get_first_key=True, no_tag_node_value_mangle=True)
+    sr = conf.get_config_dict(base, key_mangling=('-', '_'),
+                              get_first_key=True,
+                              no_tag_node_value_mangle=True,
+                              with_recursive_defaults=True)
 
-    # We have gathered the dict representation of the CLI, but there are default
-    # options which we need to update into the dictionary retrived.
-    sr = conf.merge_defaults(sr, recursive=True)
+    # FRR has VRF support for different routing daemons. As interfaces belong
+    # to VRFs - or the global VRF, we need to check for changed interfaces so
+    # that they will be properly rendered for the FRR config. Also this eases
+    # removal of interfaces from the running configuration.
+    interfaces_removed = node_changed(conf, base + ['interface'])
+    if interfaces_removed:
+        sr['interface_removed'] = list(interfaces_removed)
 
+    import pprint
+    pprint.pprint(sr)
     return sr
 
-def verify(static):
+def verify(sr):
+    if 'srv6' in sr:
+        srv6_enable = False
+        if 'interface' in sr:
+            for interface, interface_config in sr['interface'].items():
+                if 'srv6' in interface_config:
+                    srv6_enable = True
+                    break
+        if not srv6_enable:
+            raise ConfigError('SRv6 should be enabled on at least one interface!')
     return None
 
-def generate(static):
-    if not static:
+def generate(sr):
+    if not sr:
         return None
 
-    static['new_frr_config'] = render_to_string('frr/zebra.segment_routing.frr.j2', static)
+    sr['new_frr_config'] = render_to_string('frr/zebra.segment_routing.frr.j2', sr)
     return None
 
-def apply(static):
+def apply(sr):
     zebra_daemon = 'zebra'
 
+    if 'interface_removed' in sr:
+        for interface in sr['interface_removed']:
+            # Disable processing of IPv6-SR packets
+            sysctl_write(f'net.ipv6.conf.{interface}.seg6_enabled', '0')
+
+    if 'interface' in sr:
+        for interface, interface_config in sr['interface'].items():
+            # Accept or drop SR-enabled IPv6 packets on this interface
+            if 'srv6' in interface_config:
+                sysctl_write(f'net.ipv6.conf.{interface}.seg6_enabled', '1')
+                # Define HMAC policy for ingress SR-enabled packets on this interface
+                # It's a redundant check as HMAC has a default value - but better safe
+                # then sorry
+                tmp = dict_search('srv6.hmac', interface_config)
+                if tmp == 'accept':
+                    sysctl_write(f'net.ipv6.conf.{interface}.seg6_require_hmac', '0')
+                elif tmp == 'drop':
+                    sysctl_write(f'net.ipv6.conf.{interface}.seg6_require_hmac', '1')
+                elif tmp == 'ignore':
+                    sysctl_write(f'net.ipv6.conf.{interface}.seg6_require_hmac', '-1')
+            else:
+                sysctl_write(f'net.ipv6.conf.{interface}.seg6_enabled', '0')
+
     # Save original configuration prior to starting any commit actions
     frr_cfg = frr.FRRConfig()
     frr_cfg.load_configuration(zebra_daemon)
     frr_cfg.modify_section(r'^segment-routing')
-    if 'new_frr_config' in static:
-        frr_cfg.add_before(frr.default_add_before, static['new_frr_config'])
+    if 'new_frr_config' in sr:
+        frr_cfg.add_before(frr.default_add_before, sr['new_frr_config'])
     frr_cfg.commit_configuration(zebra_daemon)
 
     return None
diff --git a/src/etc/sysctl.d/30-vyos-router.conf b/src/etc/sysctl.d/30-vyos-router.conf
index 1c9b8999f..6291be5f0 100644
--- a/src/etc/sysctl.d/30-vyos-router.conf
+++ b/src/etc/sysctl.d/30-vyos-router.conf
@@ -105,3 +105,6 @@ net.core.rps_sock_flow_entries = 32768
 net.core.default_qdisc=fq_codel
 net.ipv4.tcp_congestion_control=bbr
 
+# Disable IPv6 Segment Routing packets by default
+net.ipv6.conf.all.seg6_enabled = 0
+net.ipv6.conf.default.seg6_enabled = 0