From 50a5959f6cc2567ebd5eeac1e4a47df53e652a5e Mon Sep 17 00:00:00 2001
From: Jens Langhammer <jens.langhammer@beryju.org>
Date: Wed, 9 Sep 2020 17:21:43 +0200
Subject: [PATCH] flows/importer: fix validate writing to database not being
 reverted

---
 passbook/flows/transfer/importer.py | 40 ++++++++++++++++++-----------
 1 file changed, 25 insertions(+), 15 deletions(-)

diff --git a/passbook/flows/transfer/importer.py b/passbook/flows/transfer/importer.py
index 9c03023d9..44911d65d 100644
--- a/passbook/flows/transfer/importer.py
+++ b/passbook/flows/transfer/importer.py
@@ -1,4 +1,5 @@
 """Flow importer"""
+from contextlib import contextmanager
 from copy import deepcopy
 from json import loads
 from typing import Any, Dict
@@ -9,6 +10,7 @@ from django.apps import apps
 from django.db import transaction
 from django.db.models import Model
 from django.db.models.query_utils import Q
+from django.db.utils import IntegrityError
 from rest_framework.exceptions import ValidationError
 from rest_framework.serializers import BaseSerializer, Serializer
 from structlog import BoundLogger, get_logger
@@ -26,6 +28,15 @@ from passbook.stages.prompt.models import Prompt
 ALLOWED_MODELS = (Flow, FlowStageBinding, Stage, Policy, PolicyBinding, Prompt)
 
 
+@contextmanager
+def transaction_rollback():
+    """Enters an atomic transaction and always triggers a rollback at the end of the block."""
+    atomic = transaction.atomic()
+    atomic.__enter__()
+    yield
+    atomic.__exit__(IntegrityError, None, None)
+
+
 class FlowImporter:
     """Import Flow from json"""
 
@@ -46,11 +57,10 @@ class FlowImporter:
 
     def __update_pks_for_attrs(self, attrs: Dict[str, Any]) -> Dict[str, Any]:
         """Replace any value if it is a known primary key of an other object"""
+
         def updater(value) -> Any:
             if value in self.__pk_map:
-                self.logger.debug(
-                    "updating reference in entry", value=value
-                )
+                self.logger.debug("updating reference in entry", value=value)
                 return self.__pk_map[value]
             return value
 
@@ -118,14 +128,15 @@ class FlowImporter:
 
     def apply(self) -> bool:
         """Apply (create/update) flow json, in database transaction"""
-        sid = transaction.savepoint()
-        successful = self._apply_models()
-        if not successful:
-            self.logger.debug("Reverting changes due to error")
-            transaction.savepoint_rollback(sid)
+        try:
+            with transaction.atomic():
+                if not self._apply_models():
+                    self.logger.debug("Reverting changes due to error")
+                    raise IntegrityError
+        except IntegrityError:
             return False
-        self.logger.debug("Committing changes")
-        transaction.savepoint_commit(sid)
+        else:
+            self.logger.debug("Committing changes")
         return True
 
     def _apply_models(self) -> bool:
@@ -154,9 +165,8 @@ class FlowImporter:
         if self.__import.version != 1:
             self.logger.warning("Invalid bundle version")
             return False
-        sid = transaction.savepoint()
-        successful = self._apply_models()
-        if not successful:
-            self.logger.debug("Flow validation failed")
-        transaction.savepoint_rollback(sid)
+        with transaction_rollback():
+            successful = self._apply_models()
+            if not successful:
+                self.logger.debug("Flow validation failed")
         return successful