[Authz] Allow update settings action for system user (#34030)

When the cluster.routing.allocation.disk.watermark.flood_stage watermark
is breached, DiskThresholdMonitor marks the indices as read-only. This
failed when x-pack security was present as system user does not have the privilege
for update settings action("indices:admin/settings/update").
This commit adds the required privilege for the system user. Also added missing
debug logs when access is denied to help future debugging.
An assert statement is added to catch any missed privileges required for
system user.

Closes #33119

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/authz/privilege/SystemPrivilege.java

@@ -23,7 +23,8 @@ public final class SystemPrivilege extends Privilege {
             "indices:admin/mapping/put", // needed for recovery and shrink api
             "indices:admin/template/put", // needed for the TemplateUpgradeService
             "indices:admin/template/delete", // needed for the TemplateUpgradeService
-            "indices:admin/seq_no/global_checkpoint_sync*" // needed for global checkpoint syncs
+            "indices:admin/seq_no/global_checkpoint_sync*", // needed for global checkpoint syncs
+            "indices:admin/settings/update" // needed for DiskThresholdMonitor.markIndicesReadOnly
     ), Automatons.patterns("internal:transport/proxy/*"))); // no proxy actions for system user!
 
     private SystemPrivilege() {

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/security/authz/privilege/PrivilegeTests.java

@@ -126,6 +126,8 @@ public class PrivilegeTests extends ESTestCase {
         assertThat(predicate.test("indices:admin/seq_no/global_checkpoint_sync"), is(true));
         assertThat(predicate.test("indices:admin/seq_no/global_checkpoint_sync[p]"), is(true));
         assertThat(predicate.test("indices:admin/seq_no/global_checkpoint_sync[r]"), is(true));
+        assertThat(predicate.test("indices:admin/settings/update"), is(true));
+        assertThat(predicate.test("indices:admin/settings/foo"), is(false));
     }
 
     public void testManageCcrPrivilege() {

x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/authz/AuthorizationService.java

@@ -568,9 +568,12 @@ public class AuthorizationService extends AbstractComponent {
         }
         // check for run as
         if (authentication.getUser().isRunAs()) {
+            logger.debug("action [{}] is unauthorized for user [{}] run as [{}]", action, authUser.principal(),
+                    authentication.getUser().principal());
             return authorizationError("action [{}] is unauthorized for user [{}] run as [{}]", action, authUser.principal(),
                     authentication.getUser().principal());
         }
+        logger.debug("action [{}] is unauthorized for user [{}]", action, authUser.principal());
         return authorizationError("action [{}] is unauthorized for user [{}]", action, authUser.principal());
     }
 

x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/authz/AuthorizationServiceTests.java

@@ -240,22 +240,23 @@ public class AuthorizationServiceTests extends ESTestCase {
         future.actionGet();
     }
 
-    public void testActionsSystemUserIsAuthorized() {
-        TransportRequest request = mock(TransportRequest.class);
+    public void testActionsForSystemUserIsAuthorized() {
+        final TransportRequest request = mock(TransportRequest.class);
 
         // A failure would throw an exception
-        Authentication authentication = createAuthentication(SystemUser.INSTANCE);
-        authorize(authentication, "indices:monitor/whatever", request);
-        verify(auditTrail).accessGranted(authentication, "indices:monitor/whatever", request,
-            new String[]{SystemUser.ROLE_NAME});
-
-        authentication = createAuthentication(SystemUser.INSTANCE);
-        authorize(authentication, "internal:whatever", request);
-        verify(auditTrail).accessGranted(authentication, "internal:whatever", request, new String[]{SystemUser.ROLE_NAME});
+        final Authentication authentication = createAuthentication(SystemUser.INSTANCE);
+        final String[] actions = { "indices:monitor/whatever", "internal:whatever", "cluster:monitor/whatever", "cluster:admin/reroute",
+                "indices:admin/mapping/put", "indices:admin/template/put", "indices:admin/seq_no/global_checkpoint_sync",
+                "indices:admin/settings/update" };
+        for (String action : actions) {
+            authorize(authentication, action, request);
+            verify(auditTrail).accessGranted(authentication, action, request, new String[] { SystemUser.ROLE_NAME });
+        }
+
         verifyNoMoreInteractions(auditTrail);
     }
 
-    public void testIndicesActionsAreNotAuthorized() {
+    public void testIndicesActionsForSystemUserWhichAreNotAuthorized() {
         final TransportRequest request = mock(TransportRequest.class);
         final Authentication authentication = createAuthentication(SystemUser.INSTANCE);
         assertThrowsAuthorizationException(
@@ -265,25 +266,23 @@ public class AuthorizationServiceTests extends ESTestCase {
         verifyNoMoreInteractions(auditTrail);
     }
 
-    public void testClusterAdminActionsAreNotAuthorized() {
+    public void testClusterAdminActionsForSystemUserWhichAreNotAuthorized() {
         final TransportRequest request = mock(TransportRequest.class);
         final Authentication authentication = createAuthentication(SystemUser.INSTANCE);
         assertThrowsAuthorizationException(
             () -> authorize(authentication, "cluster:admin/whatever", request),
             "cluster:admin/whatever", SystemUser.INSTANCE.principal());
-        verify(auditTrail).accessDenied(authentication, "cluster:admin/whatever", request,
-            new String[]{SystemUser.ROLE_NAME});
+        verify(auditTrail).accessDenied(authentication, "cluster:admin/whatever", request, new String[] { SystemUser.ROLE_NAME });
         verifyNoMoreInteractions(auditTrail);
     }
 
-    public void testClusterAdminSnapshotStatusActionIsNotAuthorized() {
+    public void testClusterAdminSnapshotStatusActionForSystemUserWhichIsNotAuthorized() {
         final TransportRequest request = mock(TransportRequest.class);
         final Authentication authentication = createAuthentication(SystemUser.INSTANCE);
         assertThrowsAuthorizationException(
             () -> authorize(authentication, "cluster:admin/snapshot/status", request),
             "cluster:admin/snapshot/status", SystemUser.INSTANCE.principal());
-        verify(auditTrail).accessDenied(authentication, "cluster:admin/snapshot/status", request,
-            new String[]{SystemUser.ROLE_NAME});
+        verify(auditTrail).accessDenied(authentication, "cluster:admin/snapshot/status", request, new String[] { SystemUser.ROLE_NAME });
         verifyNoMoreInteractions(auditTrail);
     }