[Patchew-devel] [PATCH 2/2] rest: introduce generic permission framework

[Paolo Bonzini]

Until now, the REST API didn't really have a good permission system.  In
particular, it did not know about user groups.  We will need to allow
the "importer" group to add messages to any project, so it's time to
improve the permissions.  Similar to the old API, all the knowledge of
permissions is encapsulated in one class, in this case a DRF Permission
subclass.  The new class replaces the old IsAdminUserOrReadOnly and
IsMaintainerUserOrReadOnly permissions.

The hierarchy is:

- safe requests, or requests from superusers, are always allowed

- group membership grants authorization for an operation on any project,
  but only if the view allows those groups

- maintainership grants authorization for an operation on maintained projects

---
 api/rest.py        | 67 ++++++++++++++++++++++++++++++++++------------
 tests/test_rest.py | 10 +++++++
 2 files changed, 60 insertions(+), 17 deletions(-)

diff --git a/api/rest.py b/api/rest.py
index ed40a10..3e9a4a6 100644
--- a/api/rest.py
+++ b/api/rest.py
@@ -28,23 +28,46 @@ SEARCH_PARAM = 'q'
 
 # patchew-specific permission classes
 
-class IsAdminUserOrReadOnly(permissions.BasePermission):
+class PatchewPermission(permissions.BasePermission):
     """
-    Allows access only to admin users.
+    Generic code to lookup for permissions based on message and project objects.
+    The nested router's "project_pk" keyword is taken as a hint that the view
+    also has a "project" property that returns a Django object.  has_permission
+    then checks that property too.
     """
+
+    allowed_groups = ()
+
+    def is_superuser(self, request):
+        return request.user and request.user.is_superuser
+
+    def has_project_permission(self, request, view, obj):
+        return obj.maintained_by(request.user)
+
+    def has_group_permission(self, request, view):
+        for grp in request.user.groups.all():
+            if grp.name in self.allowed_groups:
+                return True
+        return False
+
+    def has_generic_permission(self, request, view):
+        return (request.method in permissions.SAFE_METHODS) or \
+               self.is_superuser(request) or \
+               self.has_group_permission(request, view)
+
     def has_permission(self, request, view):
-        return request.method in permissions.SAFE_METHODS or \
-               (request.user and request.user.is_superuser)
+        return self.has_generic_permission(request, view) or \
+               ('projects_pk' in view.kwargs and \
+                self.has_project_permission(request, view, view.project))
 
-class IsMaintainerOrReadOnly(permissions.BasePermission):
-    """
-    Allows access only to admin users or maintainers.
-    """
     def has_object_permission(self, request, view, obj):
         if isinstance(obj, Message):
             obj = obj.project
-        return request.method in permissions.SAFE_METHODS or \
-               obj.maintained_by(request.user)
+        return self.has_generic_permission(request, view) or \
+               self.has_project_permission(request, view, obj)
+
+class ImportPermission(PatchewPermission):
+    allowed_groups = ('importers',)
 
 # pluggable field for plugin support
 
@@ -85,7 +108,7 @@ class UserSerializer(serializers.HyperlinkedModelSerializer):
 class UsersViewSet(viewsets.ModelViewSet):
     queryset = User.objects.all().order_by('id')
     serializer_class = UserSerializer
-    permission_classes = (IsAdminUserOrReadOnly,)
+    permission_classes = (PatchewPermission,)
 
 # Projects
 
@@ -108,7 +131,7 @@ class ProjectSerializer(serializers.HyperlinkedModelSerializer):
 class ProjectsViewSet(viewsets.ModelViewSet):
     queryset = Project.objects.all().order_by('id')
     serializer_class = ProjectSerializer
-    permission_classes = (IsMaintainerOrReadOnly,)
+    permission_classes = (PatchewPermission,)
 
 # Common classes for series and messages
 
@@ -153,7 +176,7 @@ class BaseMessageSerializer(serializers.ModelSerializer):
 class BaseMessageViewSet(mixins.ListModelMixin, viewsets.GenericViewSet):
     serializer_class = BaseMessageSerializer
     queryset = Message.objects.all()
-    permission_classes = ()
+    permission_classes = (ImportPermission,)
     lookup_field = 'message_id'
     lookup_value_regex = '[^/]+'
 
@@ -162,11 +185,21 @@ class ProjectMessagesViewSetMixin(mixins.RetrieveModelMixin):
     def get_queryset(self):
         return self.queryset.filter(project=self.kwargs['projects_pk'])
 
-    def get_serializer_context(self):
+    @property
+    def project(self):
+        if hasattr(self, '__project'):
+            return self.__project
         try:
-            return {'project': Project.objects.get(id=self.kwargs['projects_pk']), 'request': self.request}
-        except: 
+            self.__project = Project.objects.get(id=self.kwargs['projects_pk'])
+        except:
+            self.__project = None
+        return self.__project
+
+    def get_serializer_context(self):
+        if self.project is None:
             return Http404
+        return {'project': self.project, 'request': self.request}
+
 # Series
 
 class ReplySerializer(BaseMessageSerializer):
@@ -249,7 +282,6 @@ class SeriesViewSet(BaseMessageViewSet):
     queryset = Message.objects.filter(is_series_head=True).order_by('-last_reply_date')
     filter_backends = (PatchewSearchFilter,)
     search_fields = (SEARCH_PARAM,)
-    permission_classes = (IsMaintainerOrReadOnly,)
 
 
 class ProjectSeriesViewSet(ProjectMessagesViewSetMixin,
@@ -362,6 +394,7 @@ class ResultSerializerFull(ResultSerializer):
 class ResultsViewSet(viewsets.ViewSet, generics.GenericAPIView):
     lookup_field = 'name'
     lookup_value_regex = '[^/]+'
+    permission_classes = (PatchewPermission,)
 
     def get_serializer_class(self, *args, **kwargs):
         if self.lookup_field in self.kwargs:
diff --git a/tests/test_rest.py b/tests/test_rest.py
index 3baadd5..ace58ab 100755
--- a/tests/test_rest.py
+++ b/tests/test_rest.py
@@ -78,10 +78,18 @@ class RestTest(PatchewTestCase):
         self.assertEquals(resp.data['mailing_list'], "qemu-block at nongnu.org")
         self.assertEquals(resp.data['parent_project'], self.PROJECT_BASE)
 
+    def test_project_post_no_login(self):
+        data = {
+            'name': 'keycodemapdb',
+        }
+        resp = self.api_client.post(self.REST_BASE + 'projects/', data=data)
+        self.assertEquals(resp.status_code, 403)
+
     def test_project_post_minimal(self):
         data = {
             'name': 'keycodemapdb',
         }
+        self.api_client.login(username=self.user, password=self.password)
         resp = self.api_client.post(self.REST_BASE + 'projects/', data=data)
         self.assertEquals(resp.status_code, 201)
         self.assertEquals(resp.data['resource_uri'].startswith(self.REST_BASE + 'projects/'), True)
@@ -91,6 +99,7 @@ class RestTest(PatchewTestCase):
         self.assertEquals(resp.data['name'], data['name'])
 
     def test_project_post(self):
+        self.api_client.login(username=self.user, password=self.password)
         data = {
             'name': 'keycodemapdb',
             'mailing_list': 'qemu-devel at nongnu.org',
@@ -261,6 +270,7 @@ class RestTest(PatchewTestCase):
         dp = self.get_data_path("0022-another-simple-patch.json.gz")
         with open(dp, "r") as f:
             data = f.read()
+        self.api_client.login(username=self.user, password=self.password)
         resp = self.api_client.post(self.PROJECT_BASE + "messages/", data, content_type='application/json')
         self.assertEqual(resp.status_code, 201)
         resp_get = self.api_client.get(self.PROJECT_BASE + "messages/20171023201055.21973-11-andrew.smirnov at gmail.com/")
-- 
2.17.0