Bug #30079 A check for "hidden" I_S tables is flawed
Submitted: 26 Jul 2007 16:26 Modified: 1 Nov 2007 2:59
Reporter: Sergei Golubchik Email Updates:
Status: Closed Impact on me:
None 
Category:MySQL Server: Information schema Severity:S3 (Non-critical)
Version: OS:Any
Assigned to: Sergey Glukhov CPU Architecture:Any

[26 Jul 2007 16:26] Sergei Golubchik
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)
[14 Aug 2007 10:01] Bugs System
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
[4 Oct 2007 11:25] Bugs System
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
[29 Oct 2007 8:42] Bugs System
Pushed into 5.0.52
[29 Oct 2007 8:45] Bugs System
Pushed into 5.1.23-beta
[29 Oct 2007 8:49] Bugs System
Pushed into 6.0.4-alpha
[1 Nov 2007 2:59] Paul Dubois
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.