From c6dfdf10e5938e8ee7af18e31663023fb4b8390d Mon Sep 17 00:00:00 2001
From: jeremystretch <jstretch@ns1.com>
Date: Fri, 1 Jul 2022 11:38:39 -0400
Subject: [PATCH] Introduce qs_filter_from_constraints() for constructing
 object permission QS filters

---
 netbox/netbox/authentication.py | 22 +++++++++-------------
 netbox/utilities/permissions.py | 24 ++++++++++++++++++++++++
 netbox/utilities/querysets.py   | 27 +++++++--------------------
 3 files changed, 40 insertions(+), 33 deletions(-)

diff --git a/netbox/netbox/authentication.py b/netbox/netbox/authentication.py
index 00fb3ee66..c16095fdc 100644
--- a/netbox/netbox/authentication.py
+++ b/netbox/netbox/authentication.py
@@ -9,7 +9,9 @@ from django.core.exceptions import ImproperlyConfigured
 from django.db.models import Q
 
 from users.models import ObjectPermission
-from utilities.permissions import permission_is_exempt, resolve_permission, resolve_permission_ct
+from utilities.permissions import (
+    permission_is_exempt, qs_filter_from_constraints, resolve_permission, resolve_permission_ct,
+)
 
 UserModel = get_user_model()
 
@@ -99,8 +101,10 @@ class ObjectPermissionMixin:
         if not user_obj.is_active or user_obj.is_anonymous:
             return False
 
+        object_permissions = self.get_all_permissions(user_obj)
+
         # If no applicable ObjectPermissions have been created for this user/permission, deny permission
-        if perm not in self.get_all_permissions(user_obj):
+        if perm not in object_permissions:
             return False
 
         # If no object has been specified, grant permission. (The presence of a permission in this set tells
@@ -113,21 +117,13 @@ class ObjectPermissionMixin:
         if model._meta.label_lower != '.'.join((app_label, model_name)):
             raise ValueError(f"Invalid permission {perm} for model {model}")
 
-        # Compile a query filter that matches all instances of the specified model
-        obj_perm_constraints = self.get_all_permissions(user_obj)[perm]
-        constraints = Q()
-        for perm_constraints in obj_perm_constraints:
-            if perm_constraints:
-                constraints |= Q(**perm_constraints)
-            else:
-                # Found ObjectPermission with null constraints; allow model-level access
-                constraints = Q()
-                break
+        # Compile a QuerySet filter that matches all instances of the specified model
+        qs_filter = qs_filter_from_constraints(object_permissions[perm])
 
         # Permission to perform the requested action on the object depends on whether the specified object matches
         # the specified constraints. Note that this check is made against the *database* record representing the object,
         # not the instance itself.
-        return model.objects.filter(constraints, pk=obj.pk).exists()
+        return model.objects.filter(qs_filter, pk=obj.pk).exists()
 
 
 class ObjectPermissionBackend(ObjectPermissionMixin, ModelBackend):
diff --git a/netbox/utilities/permissions.py b/netbox/utilities/permissions.py
index b11bf504a..123df9e45 100644
--- a/netbox/utilities/permissions.py
+++ b/netbox/utilities/permissions.py
@@ -1,5 +1,14 @@
 from django.conf import settings
 from django.contrib.contenttypes.models import ContentType
+from django.db.models import Q
+
+__all__ = (
+    'get_permission_for_model',
+    'permission_is_exempt',
+    'qs_filter_from_constraints',
+    'resolve_permission',
+    'resolve_permission_ct',
+)
 
 
 def get_permission_for_model(model, action):
@@ -69,3 +78,18 @@ def permission_is_exempt(name):
             return True
 
     return False
+
+
+def qs_filter_from_constraints(constraints):
+    """
+    Construct a Q filter object from an iterable of ObjectPermission constraints.
+    """
+    params = Q()
+    for constraint in constraints:
+        if constraint:
+            params |= Q(**constraint)
+        else:
+            # Found null constraint; permit model-level access
+            return Q()
+
+    return params
diff --git a/netbox/utilities/querysets.py b/netbox/utilities/querysets.py
index 97d2e8779..8ec6012bf 100644
--- a/netbox/utilities/querysets.py
+++ b/netbox/utilities/querysets.py
@@ -1,6 +1,6 @@
-from django.db.models import Q, QuerySet
+from django.db.models import QuerySet
 
-from utilities.permissions import permission_is_exempt
+from utilities.permissions import permission_is_exempt, qs_filter_from_constraints
 
 
 class RestrictedQuerySet(QuerySet):
@@ -28,23 +28,10 @@ class RestrictedQuerySet(QuerySet):
 
         # Filter the queryset to include only objects with allowed attributes
         else:
-            attrs = Q()
-            for perm_attrs in user._object_perm_cache[permission_required]:
-                if type(perm_attrs) is list:
-                    for p in perm_attrs:
-                        attrs |= Q(**p)
-                elif perm_attrs:
-                    attrs |= Q(**perm_attrs)
-                else:
-                    # Any permission with null constraints grants access to _all_ instances
-                    attrs = Q()
-                    break
-            else:
-                # for else, when no break
-                # avoid duplicates when JOIN on many-to-many fields without using DISTINCT.
-                # DISTINCT acts globally on the entire request, which may not be desirable.
-                allowed_objects = self.model.objects.filter(attrs)
-                attrs = Q(pk__in=allowed_objects)
-            qs = self.filter(attrs)
+            attrs = qs_filter_from_constraints(user._object_perm_cache[permission_required])
+            # #8715: Avoid duplicates when JOIN on many-to-many fields without using DISTINCT.
+            # DISTINCT acts globally on the entire request, which may not be desirable.
+            allowed_objects = self.model.objects.filter(attrs)
+            qs = self.filter(pk__in=allowed_objects)
 
         return qs