Security, testing and migration

This part will cover various topics:

  • configuring security
  • migrating existing instance
  • writing some unit tests

Here is the read security model I want:

  • folders, files, images and comments should have one of the following visibility:
    • public, everyone can see it
    • authenticated, only authenticated users can see it
    • restricted, only a subset of authenticated users can see it
  • managers (e.g. me) can see everything
  • only authenticated users can see people
  • everyone can see classifier entities, such as tag and zone

Also, unless explicitly specified, the visibility of an image should be the same as its parent folder, as well as visibility of a comment should be the same as the commented entity. If there is no parent entity, the default visibility is authenticated.

Regarding write security, that’s much easier: * anonymous can’t write anything * authenticated users can only add comment * managers will add the remaining stuff

Now, let’s implement that!

Proper security in CubicWeb is done at the schema level, so you don’t have to bother with it in views: users will only see what they can see automatically.

Step 1: configuring security into the schema

In schema, you can grant access according to groups, or to some RQL expressions: users get access if the expression returns some results. To implement the read security defined earlier, groups are not enough, we’ll need some RQL expression. Here is the idea:

  • add a visibility attribute on Folder, File and Comment, which may be one of the value explained above
  • add a may_be_read_by relation from Folder, File and Comment to users, which will define who can see the entity
  • security propagation will be done in hook.

So the first thing to do is to modify my cube’s schema.py to define those relations:

from yams.constraints import StaticVocabularyConstraint

class visibility(RelationDefinition):
    subject = ('Folder', 'File', 'Comment')
    object = 'String'
    constraints = [StaticVocabularyConstraint(('public', 'authenticated',
                                               'restricted', 'parent'))]
    default = 'parent'
    cardinality = '11' # required

class may_be_read_by(RelationDefinition):
    __permissions__ = {
        'read':   ('managers', 'users'),
        'add':    ('managers',),
        'delete': ('managers',),
        }

    subject = ('Folder', 'File', 'Comment',)
    object = 'CWUser'

We can note the following points:

  • we’ve added a new visibility attribute to folder, file, image and comment using a RelationDefinition
  • cardinality = ‘11’ means this attribute is required. This is usually hidden under the required argument given to the String constructor, but we can rely on this here (same thing for StaticVocabularyConstraint, which is usually hidden by the vocabulary argument)
  • the parent possible value will be used for visibility propagation
  • think to secure the may_be_read_by permissions, else any user can add/delete it by default, which somewhat breaks our security model…

Now, we should be able to define security rules in the schema, based on these new attribute and relation. Here is the code to add to schema.py:

from cubicweb.schema import ERQLExpression

VISIBILITY_PERMISSIONS = {
    'read':   ('managers',
               ERQLExpression('X visibility "public"'),
               ERQLExpression('X may_be_read_by U')),
    'add':    ('managers',),
    'update': ('managers', 'owners',),
    'delete': ('managers', 'owners'),
    }
AUTH_ONLY_PERMISSIONS = {
        'read':   ('managers', 'users'),
        'add':    ('managers',),
        'update': ('managers', 'owners',),
        'delete': ('managers', 'owners'),
        }
CLASSIFIERS_PERMISSIONS = {
        'read':   ('managers', 'users', 'guests'),
        'add':    ('managers',),
        'update': ('managers', 'owners',),
        'delete': ('managers', 'owners'),
        }

from cubes.folder.schema import Folder
from cubes.file.schema import File
from cubes.comment.schema import Comment
from cubes.person.schema import Person
from cubes.zone.schema import Zone
from cubes.tag.schema import Tag

Folder.__permissions__ = VISIBILITY_PERMISSIONS
File.__permissions__ = VISIBILITY_PERMISSIONS
Comment.__permissions__ = VISIBILITY_PERMISSIONS.copy()
Comment.__permissions__['add'] = ('managers', 'users',)
Person.__permissions__ = AUTH_ONLY_PERMISSIONS
Zone.__permissions__ = CLASSIFIERS_PERMISSIONS
Tag.__permissions__ = CLASSIFIERS_PERMISSIONS

What’s important in there:

  • VISIBILITY_PERMISSIONS provides read access to managers group, if visibility attribute’s value is ‘public’, or if user (designed by the ‘U’ variable in the expression) is linked to the entity (the ‘X’ variable) through the may_be_read_by permission
  • we modify permissions of the entity types we use by importing them and modifying their __permissions__ attribute
  • notice the .copy(): we only want to modify ‘add’ permission for Comment, not for all entity types using VISIBILITY_PERMISSIONS!
  • the remaining part of the security model is done using regular groups:
    • users is the group to which all authenticated users will belong
    • guests is the group of anonymous users

Step 2: security propagation in hooks

To fullfill the requirements, we have to implement:

Also, unless explicity specified, visibility of an image should be the same as
its parent folder, as well as visibility of a comment should be the same as the
commented entity.

This kind of active rule will be done using CubicWeb’s hook system. Hooks are triggered on database events such as addition of a new entity or relation.

The tricky part of the requirement is in unless explicitly specified, notably because when the entity is added, we don’t know yet its ‘parent’ entity (e.g. Folder of an File, File commented by a Comment). To handle such things, CubicWeb provides Operation, which allow to schedule things to do at commit time.

In our case we will:

  • on entity creation, schedule an operation that will set default visibility
  • when a “parent” relation is added, propagate parent’s visibility unless the child already has a visibility set

Here is the code in cube’s hooks.py:

from cubicweb.predicates import is_instance
from cubicweb.server import hook

class SetVisibilityOp(hook.DataOperationMixIn, hook.Operation):

    def precommit_event(self):
        for eid in self.get_data():
            entity = self.cnx.entity_from_eid(eid)
            if entity.visibility == 'parent':
                entity.cw_set(visibility=u'authenticated')

class SetVisibilityHook(hook.Hook):
    __regid__ = 'sytweb.setvisibility'
    __select__ = hook.Hook.__select__ & is_instance('Folder', 'File', 'Comment')
    events = ('after_add_entity',)

    def __call__(self):
        SetVisibilityOp.get_instance(self._cw).add_data(self.entity.eid)

class SetParentVisibilityHook(hook.Hook):
    __regid__ = 'sytweb.setparentvisibility'
    __select__ = hook.Hook.__select__ & hook.match_rtype('filed_under', 'comments')
    events = ('after_add_relation',)

    def __call__(self):
        parent = self._cw.entity_from_eid(self.eidto)
        child = self._cw.entity_from_eid(self.eidfrom)
        if child.visibility == 'parent':
            child.cw_set(visibility=parent.visibility)

Notice:

  • hooks are application objects, hence have selectors that should match entity or relation types to which the hook applies. To match a relation type, we use the hook specific match_rtype selector.
  • usage of DataOperationMixIn: instead of adding an operation for each added entity, DataOperationMixIn allows to create a single one and to store entity’s eids to be processed in the transaction data. This is a good pratice to avoid heavy operations manipulation cost when creating a lot of entities in the same transaction.
  • the precommit_event method of the operation will be called at transaction’s commit time.
  • in a hook, self._cw is the repository session, not a web request as usually in views
  • according to hook’s event, you have access to different attributes on the hook instance. Here:
    • self.entity is the newly added entity on ‘after_add_entity’ events
    • self.eidfrom / self.eidto are the eid of the subject / object entity on ‘after_add_relation’ events (you may also get the relation type using self.rtype)

The parent visibility value is used to tell “propagate using parent security” because we want that attribute to be required, so we can’t use None value else we’ll get an error before we get any chance to propagate…

Now, we also want to propagate the may_be_read_by relation. Fortunately, CubicWeb provides some base hook classes for such things, so we only have to add the following code to hooks.py:

# relations where the "parent" entity is the subject
S_RELS = set()
# relations where the "parent" entity is the object
O_RELS = set(('filed_under', 'comments',))

class AddEntitySecurityPropagationHook(hook.PropagateRelationHook):
    """propagate permissions when new entity are added"""
    __regid__ = 'sytweb.addentity_security_propagation'
    __select__ = (hook.PropagateRelationHook.__select__
                  & hook.match_rtype_sets(S_RELS, O_RELS))
    main_rtype = 'may_be_read_by'
    subject_relations = S_RELS
    object_relations = O_RELS

class AddPermissionSecurityPropagationHook(hook.PropagateRelationAddHook):
    """propagate permissions when new entity are added"""
    __regid__ = 'sytweb.addperm_security_propagation'
    __select__ = (hook.PropagateRelationAddHook.__select__
                  & hook.match_rtype('may_be_read_by',))
    subject_relations = S_RELS
    object_relations = O_RELS

class DelPermissionSecurityPropagationHook(hook.PropagateRelationDelHook):
    __regid__ = 'sytweb.delperm_security_propagation'
    __select__ = (hook.PropagateRelationDelHook.__select__
                  & hook.match_rtype('may_be_read_by',))
    subject_relations = S_RELS
    object_relations = O_RELS
  • the AddEntitySecurityPropagationHook will propagate the relation when filed_under or comments relations are added
    • the S_RELS and O_RELS set as well as the match_rtype_sets selector are used here so that if my cube is used by another one, it’ll be able to configure security propagation by simply adding relation to one of the two sets.
  • the two others will propagate permissions changes on parent entities to children entities

Step 3: testing our security

Security is tricky. Writing some tests for it is a very good idea. You should even write them first, as Test Driven Development recommends!

Here is a small test case that will check the basis of our security model, in test/unittest_sytweb.py:

from cubicweb.devtools.testlib import CubicWebTC
from cubicweb import Binary

class SecurityTC(CubicWebTC):

    def test_visibility_propagation(self):
        with self.admin_access.repo_cnx() as cnx:
            # create a user for later security checks
            toto = self.create_user(cnx, 'toto')
            cnx.commit()
            # init some data using the default manager connection
            folder = cnx.create_entity('Folder',
                                       name=u'restricted',
                                       visibility=u'restricted')
            photo1 = cnx.create_entity('File',
                                       data_name=u'photo1.jpg',
                                       data=Binary('xxx'),
                                       filed_under=folder)
            cnx.commit()
            # visibility propagation
            self.assertEquals(photo1.visibility, 'restricted')
            # unless explicitly specified
            photo2 = cnx.create_entity('File',
                                       data_name=u'photo2.jpg',
                                       data=Binary('xxx'),
                                       visibility=u'public',
                                       filed_under=folder)
            cnx.commit()
            self.assertEquals(photo2.visibility, 'public')
        with self.new_access('toto').repo_cnx() as cnx:
            # test security
            self.assertEqual(1, len(cnx.execute('File X'))) # only the public one
            self.assertEqual(0, len(cnx.execute('Folder X'))) # restricted...
        with self.admin_access.repo_cnx() as cnx:
            # may_be_read_by propagation
            folder = cnx.entity_from_eid(folder.eid)
            folder.cw_set(may_be_read_by=toto)
            cnx.commit()
        with self.new_access('toto').repo_cnx() as cnx:
            photo1 = cnx.entity_from_eid(photo1.eid)
            self.failUnless(photo1.may_be_read_by)
            # test security with permissions
            self.assertEquals(2, len(cnx.execute('File X'))) # now toto has access to photo2
            self.assertEquals(1, len(cnx.execute('Folder X'))) # and to restricted folder

if __name__ == '__main__':
    from logilab.common.testlib import unittest_main
    unittest_main()

It’s not complete, but shows most things you’ll want to do in tests: adding some content, creating users and connecting as them in the test, etc…

To run it type:

$ python test/unittest_sytweb.py
========================  unittest_sytweb.py  ========================
-> creating tables [....................]
-> inserting default user and default groups.
-> storing the schema in the database [....................]
-> database for instance data initialized.
.
----------------------------------------------------------------------
Ran 1 test in 22.547s

OK

The first execution is taking time, since it creates a sqlite database for the test instance. The second one will be much quicker:

$ python test/unittest_sytweb.py
========================  unittest_sytweb.py  ========================
.
----------------------------------------------------------------------
Ran 1 test in 2.662s

OK

If you do some changes in your schema, you’ll have to force regeneration of that database. You do that by removing the tmpdb files before running the test:

$ rm data/database/tmpdb*

Step 4: writing the migration script and migrating the instance

Prior to those changes, I created an instance, fed it with some data, so I don’t want to create a new one, but to migrate the existing one. Let’s see how to do that.

Migration commands should be put in the cube’s migration directory, in a file named file:<X.Y.Z>_Any.py (‘Any’ being there mostly for historical reasons).

Here I’ll create a migration/0.2.0_Any.py file containing the following instructions:

add_relation_type('may_be_read_by')
add_relation_type('visibility')
sync_schema_props_perms()

Then I update the version number in the cube’s __pkginfo__.py to 0.2.0. And that’s it! Those instructions will:

  • update the instance’s schema by adding our two new relations and update the underlying database tables accordingly (the first two instructions)
  • update schema’s permissions definition (the last instruction)

To migrate my instance I simply type:

cubicweb-ctl upgrade sytweb_instance

You’ll then be asked some questions to do the migration step by step. You should say YES when it asks if a backup of your database should be done, so you can get back to initial state if anything goes wrong…