Re: Virtual generated columns

On Thu, Jan 9, 2025 at 12:14 AM Peter Eisentraut <peter@eisentraut.org> wrote:
>
> Here is a new patch version where I have gathered various pieces of
> feedback and improvement suggestions that are scattered over this
> thread.  I hope I got them all.  I will respond to the respective
> messages directly to give my response to each item.
>
> One thing I could use some review on is the access control handling and
> security in general.  You can create virtual generated columns that have
> their own access privileges but which can read columns that the user
> does not have access to.  Kind of like a view.  This all appears to work
> correctly, but maybe someone wants to poke a hole into it.
>
> Here is an example:
>
> create user foo;
> create user bar;
> grant create on schema public to foo;
> \c - foo
> create table t1 (id int, ccnum text, ccredacted text generated always as
> (repeat('*', 12) || substr(ccnum, 13, 4)) virtual);
> grant select (id, ccredacted) on table t1 to bar;
> insert into t1 values (1, '1234567890123456');
> \c - bar
> select * from t1;  -- permission denied
> select id, ccredacted from t1;  -- ok

I think this is expected.
however once the user can access the pg_catalog,
then he can use pg_get_expr
figure out the generation expression.

so here "bar" can figure out the column value of ccnum, i think.