Thread: function with security definer

Hi
I have a lot of users for my database, but I don't want to create each 
of them as postgres user, so I tried to do this:
1. Create only postgres 3 users: admin,user,nobody
2. Login into database _only_ as nobody and execute only 1 function - 
make_login.
3. This function checks user login and password
4. If everything is ok, function switches from nobody to either user or 
admin.

Here is a body of function:

CREATE OR REPLACE FUNCTION make_login(varchar,varchar) returns integer AS'
DECLARE  login_        ALIAS for $1;  passwd_       ALIAS for $2;  access_level  integer;
BEGIN  select into access_level access_level from users   where login=login_ and passwd=passwd_;  if not found then
return-1;  end if;  if access_level=1 then    set session authorization ''user'';  end if;  if access_level=2 then
setsession authorization ''admin'';  end if;  return 1;
 
END;
' LANGUAGE 'plpgsql' SECURITY DEFINER;

Well, it doesn't work :-(
ERROR:  permission denied

Why? Everything looks ok. User nobody has acl to execute this function. 
Function is created by database owner. What else do I need?

Regards,
Tomasz Myrta

Tomasz Myrta <jasiek@klaster.net> writes:
> [ Can't do SET SESSION AUTHORIZATION in a postgres-owned function ]

That's because SET SESSION AUTHORIZATION looks to the original login
userid, not the current effective userid, to decide whether you're
allowed to do it.  If it didn't work that way, a superuser couldn't
switch to any other identity after becoming a nonprivileged user.

I don't really see why you think this kluge is better than creating
multiple database users, anyway ...
        regards, tom lane

> Tomasz Myrta <jasiek@klaster.net> writes:
> > [ Can't do SET SESSION AUTHORIZATION in a postgres-owned function ]
> 
> That's because SET SESSION AUTHORIZATION looks to the original login
> userid, not the current effective userid, to decide whether you're
> allowed to do it.  If it didn't work that way, a superuser couldn't
> switch to any other identity after becoming a nonprivileged user.
Does it mean, that SET SESSION AUTHORIZATION works the same for function 
created with "security definer" as with "security invoker"? Are there any 
other cases, when it doesn't work properly?
> I don't really see why you think this kluge is better than creating
> multiple database users, anyway ...
Well, it was just an idea. It is easier to keep all information about users 
in one table "users" than synchronizing this table with pg_shadow via 
usesysid and granting/revoking each user one by one (or adding them to 
groups). It lets me also to give each user as little rights as needed - even 
depending on which application they currently run (administration panel or 
web report)

Regards,
Tomasz Myrta

On Mon, 24 Mar 2003, Tom Lane wrote:

> Tomasz Myrta <jasiek@klaster.net> writes:
>
> > [ Can't do SET SESSION AUTHORIZATION in a postgres-owned function ]
>
> That's because SET SESSION AUTHORIZATION looks to the original login
> userid, not the current effective userid, to decide whether you're
> allowed to do it.  If it didn't work that way, a superuser couldn't
> switch to any other identity after becoming a nonprivileged user.

So what if it went like this:
- set session authorization on "logged as superuser" acts         as before
- as a bonus allow superuser owned SECURITY DEFINER functions         to set session authorization when called by
unpriv.user.
 
- it could also be possible for superuser to drop privs  permanently, with SET PERMANENT SESSION AUTHORIZATION.
(whichjust sets login ids to the new value)
 

-- 
Antti Haapala