Skip larger than /64 subnets in DHCP agent

Dnsmasq can't handle these in IPv6 so we need to skip them to avoid
a whole bunch of log noise caused by continual retrying of issues.

Closes-Bug: #1645616
Change-Id: I36d167506cc45731e3f500a0c59b70b1bc27590f

neutron/agent/linux/dhcp.py

@@ -379,6 +379,11 @@ class Dnsmasq(DhcpLocalProcess):
                                ('set:', self._TAG_PREFIX % i,
                                 cidr.network, mode, lease))
                 else:
+                    if cidr.prefixlen < 64:
+                        LOG.debug('Ignoring subnet %(subnet)s, CIDR has '
+                                  'prefix length < 64: %(cidr)s',
+                                  {'subnet': subnet.id, 'cidr': cidr})
+                        continue
                     cmd.append('--dhcp-range=%s%s,%s,%s,%d,%s' %
                                ('set:', self._TAG_PREFIX % i,
                                 cidr.network, mode,

neutron/tests/functional/agent/test_dhcp_agent.py

@@ -84,10 +84,11 @@ class DHCPAgentOVSTestFramework(base.BaseSudoTestCase):
 
         self.conf.set_override('check_child_processes_interval', 1, 'AGENT')
 
-    def network_dict_for_dhcp(self, dhcp_enabled=True, ip_version=4):
+    def network_dict_for_dhcp(self, dhcp_enabled=True, ip_version=4,
+                              prefix_override=None):
         net_id = uuidutils.generate_uuid()
         subnet_dict = self.create_subnet_dict(
-            net_id, dhcp_enabled, ip_version)
+            net_id, dhcp_enabled, ip_version, prefix_override)
         port_dict = self.create_port_dict(
             net_id, subnet_dict.id,
             mac_address=str(self._DHCP_PORT_MAC_ADDRESS),
@@ -98,12 +99,16 @@ class DHCPAgentOVSTestFramework(base.BaseSudoTestCase):
             net_id, [subnet_dict], [port_dict])
         return net_dict
 
-    def create_subnet_dict(self, net_id, dhcp_enabled=True, ip_version=4):
+    def create_subnet_dict(self, net_id, dhcp_enabled=True, ip_version=4,
+                           prefix_override=None):
+        cidr = self._IP_ADDRS[ip_version]['cidr']
+        if prefix_override is not None:
+            cidr = '/'.join((cidr.split('/')[0], str(prefix_override)))
         sn_dict = dhcp.DictModel({
             "id": uuidutils.generate_uuid(),
             "network_id": net_id,
             "ip_version": ip_version,
-            "cidr": self._IP_ADDRS[ip_version]['cidr'],
+            "cidr": cidr,
             "gateway_ip": (self.
                 _IP_ADDRS[ip_version]['gateway']),
             "enable_dhcp": dhcp_enabled,
@@ -260,6 +265,18 @@ class DHCPAgentOVSTestCase(DHCPAgentOVSTestFramework):
                                             dhcp_enabled=dhcp_enabled)
             self.assert_dhcp_resources(network, dhcp_enabled)
 
+    def test_create_subnet_with_non64_ipv6_cidrs(self):
+        # the agent should not throw exceptions on weird prefixes
+        dhcp_enabled = True
+        version = 6
+        for i in (0, 1, 41, 81, 121, 127, 128):
+            network = self.network_dict_for_dhcp(
+                dhcp_enabled, ip_version=version, prefix_override=i)
+            self.configure_dhcp_for_network(network=network,
+                                            dhcp_enabled=dhcp_enabled)
+            self.assertFalse(self.agent.needs_resync_reasons[network.id],
+                             msg="prefix size of %s triggered resync" % i)
+
     def test_agent_mtu_set_on_interface_driver(self):
         network = self.network_dict_for_dhcp()
         network["mtu"] = 789

neutron/tests/unit/agent/linux/test_dhcp.py

@@ -512,6 +512,19 @@ class FakeV6SubnetStateless(object):
         self.ipv6_ra_mode = None
 
 
+class FakeV6SubnetStatelessBadPrefixLength(object):
+    def __init__(self):
+        self.id = 'eeeeeeee-eeee-eeee-eeee-eeeeeeeeeeee'
+        self.ip_version = 6
+        self.cidr = 'ffeb:3ba5:a17a:4ba3::/56'
+        self.gateway_ip = 'ffeb:3ba5:a17a:4ba3::1'
+        self.enable_dhcp = True
+        self.dns_nameservers = []
+        self.host_routes = []
+        self.ipv6_address_mode = constants.DHCPV6_STATELESS
+        self.ipv6_ra_mode = None
+
+
 class FakeV4SubnetNoGateway(FakeV4Subnet):
     def __init__(self):
         super(FakeV4SubnetNoGateway, self).__init__()
@@ -824,6 +837,14 @@ class FakeV6NetworkStatelessDHCP(object):
         self.namespace = 'qdhcp-ns'
 
 
+class FakeV6NetworkStatelessDHCPBadPrefixLength(object):
+    def __init__(self):
+        self.id = 'bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb'
+        self.subnets = [FakeV6SubnetStatelessBadPrefixLength()]
+        self.ports = [FakeV6PortExtraOpt()]
+        self.namespace = 'qdhcp-ns'
+
+
 class FakeNetworkWithV6SatelessAndV4DHCPSubnets(object):
     def __init__(self):
         self.id = 'bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb'
@@ -1054,7 +1075,8 @@ class TestDnsmasq(TestBase):
 
     def _test_spawn(self, extra_options, network=FakeDualNetwork(),
                     max_leases=16777216, lease_duration=86400,
-                    has_static=True, no_resolv='--no-resolv'):
+                    has_static=True, no_resolv='--no-resolv',
+                    has_stateless=True):
         def mock_get_conf_file_name(kind):
             return '/dhcp/%s/%s' % (network.id, kind)
 
@@ -1087,7 +1109,7 @@ class TestDnsmasq(TestBase):
         if has_static:
             prefix = '--dhcp-range=set:tag%d,%s,static,%s%s'
             prefix6 = '--dhcp-range=set:tag%d,%s,static,%s,%s%s'
-        else:
+        elif has_stateless:
             prefix = '--dhcp-range=set:tag%d,%s,%s%s'
             prefix6 = '--dhcp-range=set:tag%d,%s,%s,%s%s'
         possible_leases = 0
@@ -1170,6 +1192,13 @@ class TestDnsmasq(TestBase):
         self._test_spawn(['--conf-file=', '--domain=openstacklocal'],
                          network, has_static=False)
 
+    def test_spawn_no_dhcp_range_bad_prefix_length(self):
+        network = FakeV6NetworkStatelessDHCPBadPrefixLength()
+        subnet = FakeV6SubnetStatelessBadPrefixLength()
+        network.subnets = [subnet]
+        self._test_spawn(['--conf-file=', '--domain=openstacklocal'],
+                         network, has_static=False, has_stateless=False)
+
     def test_spawn_cfg_dns_server(self):
         self.conf.set_override('dnsmasq_dns_servers', ['8.8.8.8'])
         self._test_spawn(['--conf-file=',