core: prevent selecting a group as a parent of itself (#6016)

* core: prevent selecting a group as a parent of itself

Signed-off-by: Jens Langhammer <jens@goauthentik.io>

* fix api error when no parent is given

Signed-off-by: Jens Langhammer <jens@goauthentik.io>

---------

Signed-off-by: Jens Langhammer <jens@goauthentik.io>

authentik/core/api/groups.py

@@ -1,5 +1,6 @@
 """Groups API Viewset"""
 from json import loads
+from typing import Optional
 
 from django.db.models.query import QuerySet
 from django.http import Http404
@@ -52,6 +53,14 @@ class GroupSerializer(ModelSerializer):
 
     num_pk = IntegerField(read_only=True)
 
+    def validate_parent(self, parent: Optional[Group]):
+        """Validate group parent (if set), ensuring the parent isn't itself"""
+        if not self.instance or not parent:
+            return parent
+        if str(parent.group_uuid) == str(self.instance.group_uuid):
+            raise ValidationError("Cannot set group as parent of itself.")
+        return parent
+
     class Meta:
         model = Group
         fields = [