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

(cherry picked from commit 774cc97eda61eb0b91df820797fb3c705d0073d5)

4 files changed, 148 insertions, 11 deletions

diff --git a/interface-definitions/protocols-segment-routing.xml.in b/interface-definitions/protocols-segment-routing.xml.in
index d461e9c5d..4308f0c91 100644
--- a/interface-definitions/protocols-segment-routing.xml.in
+++ b/interface-definitions/protocols-segment-routing.xml.in
@@ -8,6 +8,54 @@
           <priority>900</priority>
         </properties>
         <children>
+          <tagNode name="interface">
+            <properties>
+              <help>Interface specific Segment Routing options</help>
+              <completionHelp>
+                <script>${vyos_completion_dir}/list_interfaces</script>
+              </completionHelp>
+              <valueHelp>
+                <format>txt</format>
+                <description>Interface name</description>
+              </valueHelp>
+              <constraint>
+                #include <include/constraint/interface-name.xml.i>
+              </constraint>
+            </properties>
+            <children>
+              <node name="srv6">
+                <properties>
+                  <help>Accept SR-enabled IPv6 packets on this interface</help>
+                </properties>
+                <children>
+                  <leafNode name="hmac">
+                    <properties>
+                      <help>Define HMAC policy for ingress SR-enabled packets on this interface</help>
+                      <completionHelp>
+                        <list>accept drop ignore</list>
+                      </completionHelp>
+                      <valueHelp>
+                        <format>accept</format>
+                        <description>Accept packets without HMAC, validate packets with HMAC</description>
+                      </valueHelp>
+                      <valueHelp>
+                        <format>drop</format>
+                        <description>Drop packets without HMAC, validate packets with HMAC</description>
+                      </valueHelp>
+                      <valueHelp>
+                        <format>ignore</format>
+                        <description>Ignore HMAC field.</description>
+                      </valueHelp>
+                      <constraint>
+                        <regex>(accept|drop|ignore)</regex>
+                      </constraint>
+                    </properties>
+                    <defaultValue>accept</defaultValue>
+                  </leafNode>
+                </children>
+              </node>
+            </children>
+          </tagNode>
           <node name="srv6">
             <properties>
               <help>Segment-Routing SRv6 configuration</help>
diff --git a/smoketest/scripts/cli/test_protocols_segment_routing.py b/smoketest/scripts/cli/test_protocols_segment_routing.py
index 81d42b925..403c05924 100755
--- a/smoketest/scripts/cli/test_protocols_segment_routing.py
+++ b/smoketest/scripts/cli/test_protocols_segment_routing.py
@@ -20,8 +20,10 @@ import unittest
 from base_vyostest_shim import VyOSUnitTestSHIM
 
 from vyos.configsession import ConfigSessionError
+from vyos.ifconfig import Section
 from vyos.utils.process import cmd
 from vyos.utils.process import process_named_running
+from vyos.utils.system import sysctl_read
 
 base_path = ['protocols', 'segment-routing']
 PROCESS_NAME = 'zebra'
@@ -45,6 +47,7 @@ class TestProtocolsSegmentRouting(VyOSUnitTestSHIM.TestCase):
         self.assertEqual(self.daemon_pid, process_named_running(PROCESS_NAME))
 
     def test_srv6(self):
+        interfaces = Section.interfaces('ethernet', vlan=False)
         locators = {
             'foo' : { 'prefix' : '2001:a::/64' },
             'foo' : { 'prefix' : '2001:b::/64', 'usid' : {} },
@@ -55,8 +58,18 @@ class TestProtocolsSegmentRouting(VyOSUnitTestSHIM.TestCase):
             if 'usid' in locator_config:
                 self.cli_set(base_path + ['srv6', 'locator', locator, 'behavior-usid'])
 
+        # verify() - SRv6 should be enabled on at least one interface!
+        with self.assertRaises(ConfigSessionError):
+            self.cli_commit()
+        for interface in interfaces:
+            self.cli_set(base_path + ['interface', interface, 'srv6'])
+
         self.cli_commit()
 
+        for interface in interfaces:
+            self.assertEqual(sysctl_read(f'net.ipv6.conf.{interface}.seg6_enabled'), '1')
+            self.assertEqual(sysctl_read(f'net.ipv6.conf.{interface}.seg6_require_hmac'), '0') # default
+
         frrconfig = self.getFRRconfig(f'segment-routing', daemon='zebra')
         self.assertIn(f'segment-routing', frrconfig)
         self.assertIn(f' srv6', frrconfig)
@@ -65,6 +78,35 @@ class TestProtocolsSegmentRouting(VyOSUnitTestSHIM.TestCase):
             self.assertIn(f'   locator {locator}', frrconfig)
             self.assertIn(f'    prefix {locator_config["prefix"]} block-len 40 node-len 24 func-bits 16', frrconfig)
 
+    def test_srv6_sysctl(self):
+        interfaces = Section.interfaces('ethernet', vlan=False)
+
+        # HMAC accept
+        for interface in interfaces:
+            self.cli_set(base_path + ['interface', interface, 'srv6'])
+            self.cli_set(base_path + ['interface', interface, 'srv6', 'hmac', 'ignore'])
+        self.cli_commit()
+
+        for interface in interfaces:
+            self.assertEqual(sysctl_read(f'net.ipv6.conf.{interface}.seg6_enabled'), '1')
+            self.assertEqual(sysctl_read(f'net.ipv6.conf.{interface}.seg6_require_hmac'), '-1') # ignore
+
+        # HMAC drop
+        for interface in interfaces:
+            self.cli_set(base_path + ['interface', interface, 'srv6'])
+            self.cli_set(base_path + ['interface', interface, 'srv6', 'hmac', 'drop'])
+        self.cli_commit()
+
+        for interface in interfaces:
+            self.assertEqual(sysctl_read(f'net.ipv6.conf.{interface}.seg6_enabled'), '1')
+            self.assertEqual(sysctl_read(f'net.ipv6.conf.{interface}.seg6_require_hmac'), '1') # drop
+
+        # Disable SRv6 on first interface
+        first_if = interfaces[-1]
+        self.cli_delete(base_path + ['interface', first_if])
+        self.cli_commit()
+
+        self.assertEqual(sysctl_read(f'net.ipv6.conf.{first_if}.seg6_enabled'), '0')
 
 if __name__ == '__main__':
     unittest.main(verbosity=2)
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