Bug #30079 A check for "hidden" I_S tables is flawed

Description:
Certain I_S tables are "hidden" - they cannot be selected from, and only accessible as some SHOW command.

The check is implemented as

    if (!schema_table ||
        (schema_table->hidden && 
         (sql_command_flags[lex->sql_command] & CF_STATUS_COMMAND) == 0))
    {
      my_error(ER_UNKNOWN_TABLE, MYF(0),
               ptr->table_name, INFORMATION_SCHEMA_NAME.str);
      DBUG_RETURN(0);
    }

in st_select_lex::add_table_to_list(). That is, if the table is "hidden" and the sql command is not a SHOW command - MySQL pretends the table doesn't exist.

This can be easily circumvented.

How to repeat:
mysql> select * from information_schema.TABLE_NAMES;
ERROR 1109 (42S02): Unknown table 'TABLE_NAMES' in information_schema

mysql> show fields from information_schema.TABLE_NAMES;
+---------------+--------------+------+-----+---------+-------+
| Field         | Type         | Null | Key | Default | Extra |
+---------------+--------------+------+-----+---------+-------+
| TABLE_CATALOG | varchar(512) | YES  |     | NULL    |       | 
| TABLE_SCHEMA  | varchar(64)  | NO   |     | NULL    |       | 
| TABLE_NAME    | varchar(64)  | NO   |     | NULL    |       | 
| TABLE_TYPE    | varchar(64)  | NO   |     | NULL    |       | 
+---------------+--------------+------+-----+---------+-------+
4 rows in set (0.01 sec)

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/32499

ChangeSet@1.2513, 2007-08-14 14:58:25+05:00, gluh@mysql.com +3 -0
  Bug#30079 A check for "hidden" I_S tables is flawed
  added check for hidden I_S tables for 'show columns|keys' commands

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/34892

ChangeSet@1.2551, 2007-10-04 16:20:56+05:00, gluh@mysql.com +3 -0
  Bug#30079 A check for "hidden" I_S tables is flawed
  added check for hidden I_S tables for 'show columns|keys' commands

Pushed into 5.0.52

Pushed into 5.1.23-beta

Pushed into 6.0.4-alpha

Noted in 5.0.52, 5.1.23, 6.0.4 changelogs.

Some INFORMATION_SCHEMA tables are intended for internal use, but
could be accessed by using SHOW statements.