Avoid re-adding iptables rules for instances that have disappeared

The remove_filters_for_instance() method fails silently if the
instance's chain is gone (i.e. it's been deleted). If this
happens while we're refreshing security group rules, we will
not notice this case and re-add stale rules for an old instance,
breaking our firewall for new instances.

This adds a quick check after we've captured the lock to see if
the associated chain exists, and bails if it doesn't.

Change-Id: Ic75988939f82de49735d85fe99a9eecd4baf45c9
Related-bug: #1182131

nova/network/linux_net.py

@@ -191,6 +191,12 @@ class IptablesTable(object):
         self.remove_chains = set()
         self.dirty = True
 
+    def has_chain(self, name, wrap=True):
+        if wrap:
+            return name in self.chains
+        else:
+            return name in self.unwrapped_chains
+
     def add_chain(self, name, wrap=True):
         """Adds a named chain to the table.
 

nova/tests/virt/libvirt/test_driver.py

@@ -7728,6 +7728,8 @@ class IptablesFirewallTestCase(test.TestCase):
         self.mox.StubOutWithMock(self.fw,
                                  'add_filters_for_instance',
                                  use_mock_anything=True)
+        self.mox.StubOutWithMock(self.fw.iptables.ipv4['filter'],
+                                 'has_chain')
 
         self.fw.instance_rules(instance_ref,
                                mox.IgnoreArg()).AndReturn((None, None))
@@ -7735,6 +7737,8 @@ class IptablesFirewallTestCase(test.TestCase):
                                          mox.IgnoreArg(), mox.IgnoreArg())
         self.fw.instance_rules(instance_ref,
                                mox.IgnoreArg()).AndReturn((None, None))
+        self.fw.iptables.ipv4['filter'].has_chain(mox.IgnoreArg()
+                                                  ).AndReturn(True)
         self.fw.add_filters_for_instance(instance_ref, mox.IgnoreArg(),
                                          mox.IgnoreArg(), mox.IgnoreArg())
         self.mox.ReplayAll()
@@ -7743,6 +7747,26 @@ class IptablesFirewallTestCase(test.TestCase):
         self.fw.instance_info[instance_ref['id']] = (instance_ref, None)
         self.fw.do_refresh_security_group_rules("fake")
 
+    def test_do_refresh_security_group_rules_instance_disappeared(self):
+        instance1 = {'id': 1, 'uuid': 'fake-uuid1'}
+        instance2 = {'id': 2, 'uuid': 'fake-uuid2'}
+        self.fw.instance_info = {1: (instance1, 'netinfo1'),
+                                 2: (instance2, 'netinfo2')}
+        mock_filter = mock.MagicMock()
+        with mock.patch.dict(self.fw.iptables.ipv4, {'filter': mock_filter}):
+            mock_filter.has_chain.return_value = False
+            with mock.patch.object(self.fw, 'instance_rules') as mock_ir:
+                mock_ir.return_value = (None, None)
+                self.fw.do_refresh_security_group_rules('secgroup')
+                self.assertEqual(2, mock_ir.call_count)
+            # NOTE(danms): Make sure that it is checking has_chain each time,
+            # continuing to process all the instances, and never adding the
+            # new chains back if has_chain() is False
+            mock_filter.has_chain.assert_has_calls([mock.call('inst-1'),
+                                                    mock.call('inst-2')],
+                                                   any_order=True)
+            self.assertEqual(0, mock_filter.add_chain.call_count)
+
     def test_unfilter_instance_undefines_nwfilter(self):
         admin_ctxt = context.get_admin_context()
 

nova/virt/firewall.py

@@ -24,6 +24,7 @@ from nova import objects
 from nova.objects import security_group as security_group_obj
 from nova.objects import security_group_rule as security_group_rule_obj
 from nova.openstack.common.gettextutils import _
+from nova.openstack.common.gettextutils import _LI
 from nova.openstack.common import importutils
 from nova.openstack.common import log as logging
 from nova import utils
@@ -442,6 +443,13 @@ class IptablesFirewallDriver(FirewallDriver):
     @utils.synchronized('iptables', external=True)
     def _inner_do_refresh_rules(self, instance, network_info, ipv4_rules,
                                 ipv6_rules):
+        chain_name = self._instance_chain_name(instance)
+        if not self.iptables.ipv4['filter'].has_chain(chain_name):
+            LOG.info(
+                _LI('instance chain %s disappeared during refresh, '
+                    'skipping') % chain_name,
+                instance=instance)
+            return
         self.remove_filters_for_instance(instance)
         self.add_filters_for_instance(instance, network_info, ipv4_rules,
                                       ipv6_rules)