Feature suggestion: Database-Security-Modules (DSM)

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Hi PostgreSQL Hackers,

I'm developing software using PostgreSQL for several years and want to
propose a feature to improve security of (badly written?) Web-Apps.

I call it 'Database Security Modules', derived from
Linux-Security-Modules (aka SELinux, AppArmor, Tomoyo).

Of course such a feature might already exist, or is in your opinion
not a task for PostgreSQL at all. In that case please simply inform me
about my mistake ;)

What it's about:

It's to prevent SQL-Injection and/or unpriviliged data-retrievel once
the webserver has been hacked and/or the Application-Server security
measures have ceased.

How it works:

Users or Roles get attached Access-Rules to form a DSM-List.
Each Access-Rule specifies a specific query-plan, that hereby is
granted to be executed.

Why it helps:

A simple SQL-Injection could append to query sth. like ' or 1 = 1;
select * from table_with_secret_columns' to retrieve data it should
not have access to.

But, this always (?? not sure, is this true? does it help at all?)
changes the query-plans. Now we have to queries, but each doesn't have
a valid Access-Rule as the first adds a 1=1 and thus probably changes
completely and the second one never had a Rule.

Both queries will be rejected and thus render the SQL-Injection useless.

Further ideas:

Later, this could be enhanced with additional information given to the
DSM, like 'current user id', and some Access-Rules could scope queries
based on this additional information (like only allowing a specific
Query-Plan with the parameter user_id equal to the given id).
Another addition could be rate-limiting.

Convenience:

DSMs should have different modes like 'off', 'training' (logging
query-plans to copy into DSM-Lists), 'warn' (logging but not failing
violations) and of course 'enforce'.

Please let me know what you think and if you'd be interested to see a
first basic patch implementing this.

best regards,

Jan Kechel

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