MDEV-28294: set default role bypasses Replicate_Wild_Ignore_Table: mysql.%

Problem:
========
When replicating SET DEFAULT ROLE, the pre-update check (i.e. that
in set_var_default_role::check()) tries to validate the existence of
the given rules/user even when the targeted tables are ignored. When
previously issued CREATE USER/ROLE commands are ignored by the
replica because of the replication filtering rules, this results in
an error because the targeted data does not exist.

Solution:
========
Before checking that the given roles/user exist of a SET DEFAULT
ROLE command, first ensure that the mysql.user and
mysql.roles_mapping tables are not excluded by replication filters.

Reviewed By:
============
Andrei Elkin <andrei.elkin@mariadb.com>
Sergei Golubchik <serg@mariadb.com>

mysql-test/suite/rpl/r/rpl_filter_set_var_missing_data.result

+include/master-slave.inc
+[connection master]
+#
+# Set replica to ignore system mysql tables
+connection slave;
+include/stop_slave.inc
+SET @@GLOBAL.replicate_wild_ignore_table="mysql.%";
+include/start_slave.inc
+#
+# Execute grant-based commands on primary which modify mysql system
+# tables
+connection master;
+CREATE ROLE journalist;
+CREATE USER testuser@localhost IDENTIFIED by '';
+GRANT journalist to testuser@localhost;
+#
+# Execute SET commands which use the previous user/role data
+SET DEFAULT ROLE journalist for testuser@localhost;
+SET PASSWORD for testuser@localhost= PASSWORD('123');
+include/save_master_gtid.inc
+#
+# Verify primary's grant tables have the correct user/role data
+select count(*)=1 from mysql.user where User='testuser';
+count(*)=1
+1
+select count(*)=1 from mysql.roles_mapping where User='testuser';
+count(*)=1
+1
+#
+# Ensure that the replica receives all of the primary's events without
+# error
+connection slave;
+include/sync_with_master_gtid.inc
+Last_SQL_Error = 
+Last_SQL_Errno = 0
+#
+# Verify that the replica did not execute the master's commands
+select count(*)=0 from mysql.user where User='testuser';
+count(*)=0
+1
+select count(*)=0 from mysql.roles_mapping where User='testuser';
+count(*)=0
+1
+#
+# Clean up
+connection master;
+DROP ROLE journalist;
+DROP USER testuser@localhost;
+include/save_master_gtid.inc
+connection slave;
+include/sync_with_master_gtid.inc
+include/stop_slave.inc
+SET @@GLOBAL.replicate_wild_ignore_table="";
+include/start_slave.inc
+include/rpl_end.inc

mysql-test/suite/rpl/t/rpl_filter_set_var_missing_data.test

+#
+# Purpose:
+#   This test ensures that the SET DEFAULT ROLE and SET PASSWORD commands can
+# be ignored by replica filter rules. MDEV-28294 exposed a bug in which
+# SET DEFAULT ROLE would check for the existence of the given roles/user even
+# when the targeted tables are ignored, resulting in errors if the targeted
+# data does not exist. More specifically, when previously issued
+# CREATE USER/ROLE commands are ignored by the replica because of the
+# replication filtering rules, SET DEFAULT ROLE would result in an error
+# because the targeted data does not exist.
+#
+# Methodology:
+#   Using a replica configured with replicate_wild_ignore_table="mysql.%",
+# execute SET DEFAULT ROLE and SET PASSWORD on the primary and ensure that the
+# replica neither errors nor executes the commands which the primary sends.
+#
+# References:
+#   MDEV-28294: set default role bypasses Replicate_Wild_Ignore_Table: mysql.%
+#
+
+source include/master-slave.inc;
+source include/have_binlog_format_mixed.inc;
+
+--echo #
+--echo # Set replica to ignore system mysql tables
+connection slave;
+let $old_filter= query_get_value(SHOW SLAVE STATUS, Replicate_Wild_Ignore_Table, 1);
+source include/stop_slave.inc;
+SET @@GLOBAL.replicate_wild_ignore_table="mysql.%";
+source include/start_slave.inc;
+
+--echo #
+--echo # Execute grant-based commands on primary which modify mysql system
+--echo # tables
+connection master;
+CREATE ROLE journalist;
+CREATE USER testuser@localhost IDENTIFIED by '';
+GRANT journalist to testuser@localhost;
+
+--echo #
+--echo # Execute SET commands which use the previous user/role data
+SET DEFAULT ROLE journalist for testuser@localhost;
+SET PASSWORD for testuser@localhost= PASSWORD('123');
+--source include/save_master_gtid.inc
+
+--echo #
+--echo # Verify primary's grant tables have the correct user/role data
+select count(*)=1 from mysql.user where User='testuser';
+select count(*)=1 from mysql.roles_mapping where User='testuser';
+
+--echo #
+--echo # Ensure that the replica receives all of the primary's events without
+--echo # error
+connection slave;
+--source include/sync_with_master_gtid.inc
+let $error= query_get_value(SHOW SLAVE STATUS, Last_SQL_Error, 1);
+--echo Last_SQL_Error = $error
+let $errno= query_get_value(SHOW SLAVE STATUS, Last_SQL_Errno, 1);
+--echo Last_SQL_Errno = $errno
+
+--echo #
+--echo # Verify that the replica did not execute the master's commands
+select count(*)=0 from mysql.user where User='testuser';
+select count(*)=0 from mysql.roles_mapping where User='testuser';
+
+--echo #
+--echo # Clean up
+
+# The master has to drop the role/user combination while the slave still has
+# its filters active; otherwise, the slave would try to drop users/roles that
+# were never replicated.
+--connection master
+DROP ROLE journalist;
+DROP USER testuser@localhost;
+--source include/save_master_gtid.inc
+
+--connection slave
+--source include/sync_with_master_gtid.inc
+source include/stop_slave.inc;
+--eval SET @@GLOBAL.replicate_wild_ignore_table="$old_filter"
+source include/start_slave.inc;
+
+--source include/rpl_end.inc

sql/sql_acl.cc

@@ -1249,18 +1249,8 @@ class Grant_tables
     DBUG_ENTER("Grant_tables::open_and_lock");
     DBUG_ASSERT(first_table_in_list);
 #ifdef HAVE_REPLICATION
-    if (first_table_in_list->tl.lock_type >= TL_WRITE_ALLOW_WRITE &&
-        thd->slave_thread && !thd->spcont)
-    {
-      /*
-        GRANT and REVOKE are applied the slave in/exclusion rules as they are
-        some kind of updates to the mysql.% tables.
-      */
-      Rpl_filter *rpl_filter= thd->system_thread_info.rpl_sql_info->rpl_filter;
-      if (rpl_filter->is_on() &&
-          !rpl_filter->tables_ok(0, &first_table_in_list->tl))
-        DBUG_RETURN(1);
-    }
+    if (int ignore_ret= rpl_ignore_tables(thd))
+      DBUG_RETURN(ignore_ret);
 #endif
     if (open_and_lock_tables(thd, &first_table_in_list->tl, FALSE,
                              MYSQL_LOCK_IGNORE_TIMEOUT))
@@ -1290,6 +1280,32 @@ class Grant_tables
     DBUG_RETURN(0);
   }
 
+#ifdef HAVE_REPLICATION
+  /* Checks if the tables targeted by a grant command should be ignored because
+     of the configured replication filters
+
+     @retval 1 Tables are excluded for replication
+     @retval 0 tables are included for replication
+  */
+  int rpl_ignore_tables(THD *thd)
+  {
+    DBUG_ENTER("Grant_tables::rpl_ignore_tables");
+    if (first_table_in_list->tl.lock_type >= TL_WRITE_ALLOW_WRITE &&
+        thd->slave_thread && !thd->spcont)
+    {
+      /*
+        GRANT and REVOKE are applied the slave in/exclusion rules as they are
+        some kind of updates to the mysql.% tables.
+      */
+      Rpl_filter *rpl_filter= thd->system_thread_info.rpl_sql_info->rpl_filter;
+      if (rpl_filter->is_on() &&
+          !rpl_filter->tables_ok(0, &first_table_in_list->tl))
+        DBUG_RETURN(1);
+    }
+    DBUG_RETURN(0);
+  }
+#endif
+
   inline const User_table& user_table() const
   {
     return m_user_table;
@@ -3469,6 +3485,16 @@ int acl_check_set_default_role(THD *thd, const char *host, const char *user,
                                const char *role)
 {
   DBUG_ENTER("acl_check_set_default_role");
+#ifdef HAVE_REPLICATION
+  /*
+    If the roles_mapping table is excluded by the replication filter, we return
+    successful without validating the user/role data because the command will
+    be ignored in a later call to `acl_set_default_role()` for a graceful exit.
+  */
+  Grant_tables tables(Table_roles_mapping, TL_WRITE);
+  if (tables.rpl_ignore_tables(thd))
+    DBUG_RETURN(0);
+#endif
   DBUG_RETURN(check_alter_user(thd, host, user) ||
               check_user_can_set_role(thd, user, host, NULL, role, NULL));
 }