libvirt: Always copy or recreate disk.info during a migration

The disk.info file contains the path and format of any image, config or
ephermal disk associated with an instance. When using RAW images and migrating
an instance this file should always be copied or recreated. This avoids the Raw
imagebackend reinspecting the format of these disks when spawning the instance
on the destination host.

By not copying or recreating this disk.info file, a malicious image written to
an instance disk on the source host will cause Nova to reinspect and record a
different format for the disk on the destination. This format then being used
incorrectly when finally spawning the instance on the destination.

SecurityImpact
Closes-bug: #1548450
Change-Id: Idfc16f54049aaeab31ac1c1d8d79a129acc9fb87

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

@@ -8636,6 +8636,43 @@ def check_instance_dir(context, instance,
                            fallback_from_host=instance.host)])
             self.assertIsInstance(res, objects.LibvirtLiveMigrateData)
 
+    def test_pre_live_migration_recreate_disk_info(self):
+
+        migrate_data = {'is_shared_block_storage': False,
+                        'is_shared_instance_path': False,
+                        'block_migration': True,
+                        'instance_relative_path': '/some/path/'}
+        disk_info = [{'disk_size': 5368709120, 'type': 'raw',
+                      'virt_disk_size': 5368709120,
+                      'path': '/some/path/disk',
+                      'backing_file': '', 'over_committed_disk_size': 0},
+                     {'disk_size': 1073741824, 'type': 'raw',
+                      'virt_disk_size': 1073741824,
+                      'path': '/some/path/disk.eph0',
+                      'backing_file': '', 'over_committed_disk_size': 0}]
+        image_disk_info = {'/some/path/disk': 'raw',
+                           '/some/path/disk.eph0': 'raw'}
+
+        drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
+        instance = objects.Instance(**self.test_instance)
+        instance_path = os.path.dirname(disk_info[0]['path'])
+        disk_info_path = os.path.join(instance_path, 'disk.info')
+
+        with test.nested(
+            mock.patch.object(os, 'mkdir'),
+            mock.patch.object(fake_libvirt_utils, 'write_to_file'),
+            mock.patch.object(drvr, '_create_images_and_backing')
+        ) as (
+            mkdir, write_to_file, create_images_and_backing
+        ):
+            drvr.pre_live_migration(self.context, instance,
+                                    block_device_info=None,
+                                    network_info=[],
+                                    disk_info=jsonutils.dumps(disk_info),
+                                    migrate_data=migrate_data)
+            write_to_file.assert_called_with(disk_info_path,
+                                             jsonutils.dumps(image_disk_info))
+
     def test_get_instance_disk_info_works_correctly(self):
         # Test data
         instance = objects.Instance(**self.test_instance)
@@ -14170,6 +14207,44 @@ def test_migrate_disk_and_power_off_resize_error_eph(self, mock_get,
         flavor_obj = objects.Flavor(**flavor)
         self._test_migrate_disk_and_power_off(flavor_obj)
 
+    @mock.patch('nova.utils.execute')
+    @mock.patch('nova.virt.libvirt.utils.copy_image')
+    @mock.patch('nova.virt.libvirt.driver.LibvirtDriver._destroy')
+    @mock.patch('nova.virt.libvirt.utils.get_instance_path')
+    @mock.patch('nova.virt.libvirt.driver.LibvirtDriver'
+                '._is_storage_shared_with')
+    @mock.patch('nova.virt.libvirt.driver.LibvirtDriver'
+                '.get_instance_disk_info')
+    def test_migrate_disk_and_power_off_resize_copy_disk_info(self,
+                                                              mock_disk_info,
+                                                              mock_shared,
+                                                              mock_path,
+                                                              mock_destroy,
+                                                              mock_copy,
+                                                              mock_execuate):
+
+        instance = self._create_instance()
+        disk_info = self._disk_info()
+        disk_info_text = jsonutils.loads(disk_info)
+        instance_base = os.path.dirname(disk_info_text[0]['path'])
+        flavor = {'root_gb': 10, 'ephemeral_gb': 25}
+        flavor_obj = objects.Flavor(**flavor)
+
+        mock_disk_info.return_value = disk_info
+        mock_path.return_value = instance_base
+        mock_shared.return_value = False
+
+        self.drvr.migrate_disk_and_power_off(context.get_admin_context(),
+                                             instance, mock.sentinel,
+                                             flavor_obj, None)
+
+        src_disk_info_path = os.path.join(instance_base + '_resize',
+                                          'disk.info')
+        dst_disk_info_path = os.path.join(instance_base, 'disk.info')
+        mock_copy.assert_any_call(src_disk_info_path, dst_disk_info_path,
+                                  host=mock.sentinel, on_execute=mock.ANY,
+                                  on_completion=mock.ANY, compression=mock.ANY)
+
     def test_wait_for_running(self):
         def fake_get_info(instance):
             if instance['name'] == "not_found":

nova/virt/libvirt/driver.py

@@ -6655,6 +6655,24 @@ def pre_live_migration(self, context, instance, block_device_info,
                       instance=instance)
             os.mkdir(instance_dir)
 
+            # Recreate the disk.info file and in doing so stop the
+            # imagebackend from recreating it incorrectly by inspecting the
+            # contents of each file when using the Raw backend.
+            if disk_info:
+                image_disk_info = {}
+                for info in disk_info:
+                    image_file = os.path.basename(info['path'])
+                    image_path = os.path.join(instance_dir, image_file)
+                    image_disk_info[image_path] = info['type']
+
+                LOG.debug('Creating disk.info with the contents: %s',
+                          image_disk_info, instance=instance)
+
+                image_disk_info_path = os.path.join(instance_dir,
+                                                    'disk.info')
+                libvirt_utils.write_to_file(image_disk_info_path,
+                                            jsonutils.dumps(image_disk_info))
+
             if not is_shared_block_storage:
                 # Ensure images and backing files are present.
                 LOG.debug('Checking to make sure images and backing files are '
@@ -7242,6 +7260,15 @@ def migrate_disk_and_power_off(self, context, instance, dest,
                                              on_execute=on_execute,
                                              on_completion=on_completion,
                                              compression=compression)
+
+            # Ensure disk.info is written to the new path to avoid disks being
+            # reinspected and potentially changing format.
+            src_disk_info_path = os.path.join(inst_base_resize, 'disk.info')
+            dst_disk_info_path = os.path.join(inst_base, 'disk.info')
+            libvirt_utils.copy_image(src_disk_info_path, dst_disk_info_path,
+                                     host=dest, on_execute=on_execute,
+                                     on_completion=on_completion,
+                                     compression=compression)
         except Exception:
             with excutils.save_and_reraise_exception():
                 self._cleanup_remote_migration(dest, inst_base,