libvirt: Avoid using os-brick encryptors when device_path isn't provided

When disconnecting an encrypted volume the Libvirt driver uses the
presence of a Libvirt secret associated with the volume to determine if
the new style native QEMU LUKS decryption or original decryption method
using os-brick encrytors is used.

While this works well in most deployments some issues have been observed
in Kolla based environments where the Libvirt secrets are not fully
persisted between host reboots or container upgrades. This can lead to
_detach_encryptor attempting to build an encryptor which will fail if
the associated connection_info for the volume does not contain a
device_path, such as in the case for encrypted rbd volumes.

This change adds a simple conditional to _detach_encryptor to ensure we
return when device_path is not present in connection_info and native
QEMU LUKS decryption is available. This handles the specific use
case where we are certain that the encrypted volume was never decrypted
using the os-brick encryptors, as these require a local block device on
the compute host and have thus never supported rbd.

It is still safe to build an encryptor and call detach_volume when a
device_path is present however as change I9f52f89b8466d036 made such
calls idempotent within os-brick.

Change-Id: Id670f13a7f197e71c77dc91276fc2fba2fc5f314
Closes-bug: #1821696
(cherry picked from commit 56ca4d32dd)

nova/tests/unit/virt/libvirt/test_driver.py

@@ -8354,8 +8354,9 @@ class LibvirtConnTestCase(test.NoDBTestCase,
 
     @mock.patch('os_brick.encryptors.get_encryption_metadata')
     @mock.patch('nova.virt.libvirt.driver.LibvirtDriver._get_volume_encryptor')
+    @mock.patch('nova.virt.libvirt.driver.LibvirtDriver._use_native_luks')
     def test_detach_encryptor_encrypted_volume_meta_missing(self,
-            mock_get_encryptor, mock_get_metadata):
+            mock_use_native_luks, mock_get_encryptor, mock_get_metadata):
         """Assert that if missing the encryption metadata of an encrypted
         volume is fetched and then used to detach the encryptor for the volume.
         """
@@ -8365,6 +8366,7 @@ class LibvirtConnTestCase(test.NoDBTestCase,
         encryption = {'provider': 'luks', 'control_location': 'front-end'}
         mock_get_metadata.return_value = encryption
         connection_info = {'data': {'volume_id': uuids.volume_id}}
+        mock_use_native_luks.return_value = False
 
         drvr._detach_encryptor(self.context, connection_info, None)
 
@@ -8376,8 +8378,9 @@ class LibvirtConnTestCase(test.NoDBTestCase,
 
     @mock.patch('os_brick.encryptors.get_encryption_metadata')
     @mock.patch('nova.virt.libvirt.driver.LibvirtDriver._get_volume_encryptor')
+    @mock.patch('nova.virt.libvirt.driver.LibvirtDriver._use_native_luks')
     def test_detach_encryptor_encrypted_volume_meta_provided(self,
-            mock_get_encryptor, mock_get_metadata):
+            mock_use_native_luks, mock_get_encryptor, mock_get_metadata):
         """Assert that when provided there are no further attempts to fetch the
         encryption metadata for the volume and that the provided metadata is
         then used to detach the volume.
@@ -8387,6 +8390,7 @@ class LibvirtConnTestCase(test.NoDBTestCase,
         mock_get_encryptor.return_value = mock_encryptor
         encryption = {'provider': 'luks', 'control_location': 'front-end'}
         connection_info = {'data': {'volume_id': uuids.volume_id}}
+        mock_use_native_luks.return_value = False
 
         drvr._detach_encryptor(self.context, connection_info, encryption)
 
@@ -8395,6 +8399,27 @@ class LibvirtConnTestCase(test.NoDBTestCase,
                                                    encryption)
         mock_encryptor.detach_volume.assert_called_once_with(**encryption)
 
+    @mock.patch('nova.virt.libvirt.host.Host.find_secret')
+    @mock.patch('nova.virt.libvirt.driver.LibvirtDriver._use_native_luks')
+    @mock.patch('nova.virt.libvirt.driver.LibvirtDriver._get_volume_encryptor')
+    def test_detach_encryptor_native_luks_device_path_secret_missing(self,
+            mock_get_encryptor, mock_use_native_luks, mock_find_secret):
+        """Assert that the encryptor is not built when native LUKS is
+        available, the associated volume secret is missing and device_path is
+        also missing from the connection_info.
+        """
+        drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
+        encryption = {'provider': 'luks', 'control_location': 'front-end',
+                      'encryption_key_id': uuids.encryption_key_id}
+        connection_info = {'data': {'volume_id': uuids.volume_id}}
+        mock_find_secret.return_value = False
+        mock_use_native_luks.return_value = True
+
+        drvr._detach_encryptor(self.context, connection_info, encryption)
+
+        mock_find_secret.assert_called_once_with('volume', uuids.volume_id)
+        mock_get_encryptor.assert_not_called()
+
     @mock.patch.object(host.Host, "has_min_version")
     def test_use_native_luks(self, mock_has_min_version):
         drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)

nova/virt/libvirt/driver.py

@@ -1435,6 +1435,14 @@ class LibvirtDriver(driver.ComputeDriver):
             return self._host.delete_secret('volume', volume_id)
         if encryption is None:
             encryption = self._get_volume_encryption(context, connection_info)
+        # NOTE(lyarwood): Handle bug #1821696 where volume secrets have been
+        # removed manually by returning if native LUKS decryption is available
+        # and device_path is not present in the connection_info. This avoids
+        # VolumeEncryptionNotSupported being thrown when we incorrectly build
+        # the encryptor below due to the secrets not being present above.
+        if (encryption and self._use_native_luks(encryption) and
+            not connection_info['data'].get('device_path')):
+            return
         if encryption:
             encryptor = self._get_volume_encryptor(connection_info,
                                                    encryption)