Re: information_schema for all users

On Sun, Jul 09, 2006 at 09:52:35AM +0200, Luca Giandoso wrote:
> I wold like to make a plpgsql function that return column names and
> their data types of a specific table.

Do you have a reason for returning a cursor instead of SETOF some
type? In versions prior to 8.1 you could create a custom type for
the return columns; in 8.1 you could use OUT parameters and return
SETOF record.

[snip function that returns a cursor over information_schema.columns]

> but it works only with the database owner although i have used
> "SECURITY DEFINER".

The information_schema privilege checks are based on current_user,
which is apparently evaluated when you fetch rows from the cursor,
not when you open the cursor. Here's a simple example; we'll create
the following function as user alice:

CREATE FUNCTION testfunc(refcursor) RETURNS refcursor AS $$
BEGIN
RAISE INFO 'current_user = %', current_user;
OPEN $1 FOR SELECT current_user;
RETURN $1;
END;
$$ LANGUAGE plpgsql SECURITY DEFINER;

First we'll call the function as alice; notice that the current_user
displayed by the RAISE statement is the same as the current_user
fetched by the cursor:

test=> BEGIN; SELECT testfunc('curs'); FETCH curs; COMMIT;
BEGIN
INFO: current_user = alice
testfunc
----------
curs
(1 row)

current_user
--------------
alice
(1 row)

COMMIT

Now we'll call the same function as user bob; notice that the
current_user displayed by the RAISE statement is "alice" because
of SECURITY DEFINER but that the current_user displayed when fetching
from the cursor is "bob":

test=> \c - bob
Password for user bob:
You are now connected as new user "bob".
test=> BEGIN; SELECT testfunc('curs'); FETCH curs; COMMIT;
BEGIN
INFO: current_user = alice
testfunc
----------
curs
(1 row)

current_user
--------------
bob
(1 row)

COMMIT

I don't know if this behavior is intentional but that's how it
currently works. You could avoid it by returning SETOF some type
rather than a cursor, or you could query the PostgreSQL system
catalogs directly instead of using information_schema. If you're
returning the results of a simple query, and if you can make that
query work without SECURITY DEFINER, then you could use a view
instead of a function.

--
Michael Fuhr