Move get_trust enforcement to default policies

Without this change, policy enforcement for the GET
/OS-TRUST/trusts/{trust_id} API is hardcoded in the flask dispatcher
code. This is a problem because this enforcement can't be controlled by
the operator, as is the norm. Moreover, it makes the transition to
system-scope and default-roles-aware policies more difficult because
there's no sensible migration from "" to a logical role-based check
string.

This converts the hardcoded enforcement to enforcement via default
policies for GET /OS-TRUST/trusts/{trust_id}. The API specifically
blocks the is_admin user from using it, and since policies aren't loaded
for the is_admin user we need to continue explicitly blocking it.

This change does not use the formal oslo.policy deprecation system
because "" OR'd with the new default is entirely useless as a policy.

Change-Id: I3c0718330d5a18c0c79e8f12509200fd97a55913
Partial-bug: #1818850
Partial-bug: #1818846

keystone/api/trusts.py

@@ -164,9 +164,39 @@ class TrustResource(ks_flask.ResourceBase):
         return roles
 
     def _get_trust(self, trust_id):
-        ENFORCER.enforce_call(action='identity:get_trust')
+        ENFORCER.enforce_call(action='identity:get_trust',
+                              build_target=_build_trust_target_enforcement)
+
+        # NOTE(cmurphy) look up trust before doing is_admin authorization - to
+        # maintain the API contract, we expect a missing trust to raise a 404
+        # before we get to enforcement (lp#1840288)
         trust = PROVIDERS.trust_api.get_trust(trust_id)
-        _trustor_trustee_only(trust)
+
+        if self.oslo_context.is_admin:
+            # policies are not loaded for the is_admin context, so need to
+            # block access here
+            raise exception.ForbiddenAction(
+                action=_('Requested user has no relation to this trust'))
+
+        # NOTE(cmurphy) As of Train, the default policies enforce the
+        # identity:get_trust rule. However, in case the
+        # identity:get_trust rule has been locally overridden by the
+        # default that would have been produced by the sample config, we need
+        # to enforce it again and warn that the behavior is changing.
+        rules = policy._ENFORCER._enforcer.rules.get('identity:get_trust')
+        # rule check_str is ""
+        if isinstance(rules, op_checks.TrueCheck):
+            LOG.warning(
+                "The policy check string for rule \"identity:get_trust\" "
+                "has been overridden to \"always true\". In the next release, "
+                "this will cause the" "\"identity:get_trust\" action to "
+                "be fully permissive as hardcoded enforcement will be "
+                "removed. To correct this issue, either stop overriding the "
+                "\"identity:get_trust\" rule in config to accept the "
+                "defaults, or explicitly set a rule that is not empty."
+            )
+            _trustor_trustee_only(trust)
+
         _normalize_trust_expires_at(trust)
         _normalize_trust_roles(trust)
         return self.wrap_member(trust)

keystone/cmd/status.py

@@ -34,7 +34,11 @@ class Checks(upgradecheck.UpgradeCommands):
         enforcer = policy.Enforcer(CONF)
         ENFORCER.register_rules(enforcer)
         enforcer.load_rules()
-        rules = ['identity:list_trusts', 'identity:delete_trust']
+        rules = [
+            'identity:list_trusts',
+            'identity:delete_trust',
+            'identity:get_trust'
+        ]
         failed_rules = []
         for rule in rules:
             current_rule = enforcer.rules.get(rule)

keystone/common/policies/trust.py

@@ -82,7 +82,7 @@ trust_policies = [
                      'method': 'DELETE'}]),
     policy.DocumentedRuleDefault(
         name=base.IDENTITY % 'get_trust',
-        check_str='',
+        check_str=RULE_TRUSTOR + ' or ' + RULE_TRUSTEE,
         scope_types=['project'],
         description='Get trust.',
         operations=[{'path': '/v3/OS-TRUST/trusts/{trust_id}',

keystone/tests/unit/protection/v3/test_trusts.py

@@ -110,6 +110,7 @@ class TrustTests(base_classes.TestCaseWithBootstrap,
             overridden_policies = {
                 'identity:list_trusts': '',
                 'identity:delete_trust': '',
+                'identity:get_trust': '',
             }
             f.write(jsonutils.dumps(overridden_policies))
 
@@ -272,6 +273,18 @@ class SystemAdminTests(TrustTests, _AdminTestsMixin):
                 expected_status_code=http_client.FORBIDDEN
             )
 
+    def test_admin_cannot_get_trust_for_other_user_overridden_defaults(self):
+        self._override_policy_old_defaults()
+        PROVIDERS.trust_api.create_trust(
+            self.trust_id, **self.trust_data)
+
+        with self.test_client() as c:
+            c.get(
+                '/v3/OS-TRUST/trusts/%s' % self.trust_id,
+                headers=self.headers,
+                expected_status_code=http_client.FORBIDDEN
+            )
+
 
 class ProjectUserTests(TrustTests):
     """Tests for all project users."""
@@ -646,3 +659,26 @@ class ProjectUserTests(TrustTests):
                 headers=self.other_headers,
                 expected_status_code=http_client.FORBIDDEN
             )
+
+    def test_user_can_get_trust_of_whom_they_are_the_trustor_overridden_default(self):
+        self._override_policy_old_defaults()
+        ref = PROVIDERS.trust_api.create_trust(
+            self.trust_id, **self.trust_data)
+
+        with self.test_client() as c:
+            c.get(
+                '/v3/OS-TRUST/trusts/%s' % ref['id'],
+                headers=self.trustor_headers
+            )
+
+    def test_user_can_get_trust_delegated_to_them_overridden_default(self):
+        self._override_policy_old_defaults()
+        ref = PROVIDERS.trust_api.create_trust(
+            self.trust_id, **self.trust_data)
+
+        with self.test_client() as c:
+            r = c.get(
+                '/v3/OS-TRUST/trusts/%s' % ref['id'],
+                headers=self.trustee_headers
+            )
+        self.assertEqual(r.json['trust']['id'], self.trust_id)

keystone/tests/unit/test_cli.py

@@ -1866,7 +1866,8 @@ class CliStatusTestCase(unit.SQLDriverOverrides, unit.TestCase):
         with open(self.policy_file_name, 'w') as f:
             overridden_policies = {
                 'identity:list_trusts': '',
-                'identity:delete_trust': ''
+                'identity:delete_trust': '',
+                'identity:get_trust': ''
             }
             f.write(jsonutils.dumps(overridden_policies))
         result = self.checks.check_trust_policies_are_not_empty()
@@ -1874,7 +1875,8 @@ class CliStatusTestCase(unit.SQLDriverOverrides, unit.TestCase):
         with open(self.policy_file_name, 'w') as f:
             overridden_policies = {
                 'identity:list_trusts': 'rule:admin_required',
-                'identity:delete_trust': 'rule:admin_required'
+                'identity:delete_trust': 'rule:admin_required',
+                'identity:get_trust': 'rule:admin_required'
             }
             f.write(jsonutils.dumps(overridden_policies))
         result = self.checks.check_trust_policies_are_not_empty()