MDEV-16987 - ALTER DATABASE possible in read-only mode

Forbid ALTER DATABASE under read_only.

mysql-test/r/read_only.result

@@ -162,3 +162,14 @@ delete from mysql.columns_priv where User like 'mysqltest_%';
 flush privileges;
 drop database mysqltest_db1;
 set global read_only= @start_read_only;
+#
+# MDEV-16987 - ALTER DATABASE possible in read-only mode
+#
+GRANT ALTER ON test1.* TO user1@localhost;
+CREATE DATABASE test1;
+SET GLOBAL read_only=1;
+ALTER DATABASE test1 CHARACTER SET utf8;
+ERROR HY000: The MariaDB server is running with the --read-only option so it cannot execute this statement
+SET GLOBAL read_only=0;
+DROP DATABASE test1;
+DROP USER user1@localhost;

mysql-test/t/read_only.test

@@ -310,3 +310,16 @@ set global read_only= @start_read_only;
 # Wait till all disconnects are completed
 --source include/wait_until_count_sessions.inc
 
+--echo #
+--echo # MDEV-16987 - ALTER DATABASE possible in read-only mode
+--echo #
+GRANT ALTER ON test1.* TO user1@localhost;
+CREATE DATABASE test1;
+SET GLOBAL read_only=1;
+change_user user1;
+--error ER_OPTION_PREVENTS_STATEMENT
+ALTER DATABASE test1 CHARACTER SET utf8;
+change_user root;
+SET GLOBAL read_only=0;
+DROP DATABASE test1;
+DROP USER user1@localhost;

sql/sql_parse.cc

@@ -831,6 +831,7 @@ static bool deny_updates_if_read_only_option(THD *thd, TABLE_LIST *all_tables)
     DBUG_RETURN(FALSE);
 
   if (lex->sql_command == SQLCOM_CREATE_DB ||
+      lex->sql_command == SQLCOM_ALTER_DB ||
       lex->sql_command == SQLCOM_DROP_DB)
     DBUG_RETURN(TRUE);