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Re: User Privileges using dblink

From: "Darko Prenosil" <Darko(dot)Prenosil(at)finteh(dot)hr>
To: <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: User Privileges using dblink
Date: 2004-06-29 17:37:57
Message-ID: 002701c45dff$e7df6f00$1e82bfd5@darko (view raw or flat)
Thread:
Lists: pgsql-hackers
Write a function that returns connection parameters (instead of hardcoding
it into view) using CURENT_USER as parameter.

create view inst as select * from dblink(
get_connection_param(CURRENT_USER) )

where get_connection_param is Your function returning text. Using system
user name is not problem at all, but password is.
You can read encrypted password from pg_shadow but only if You are a
superuser, otherwise it is another security hole...

However this is not a dblink problem, and can be summarized as:
    How can I know my own password ?

I think that even server does not know Your password, it only knows
encrypted presentation (someone else could know this better).

Regards !


----- Original Message -----
From: "Kreißl, Karsten" <KREISSL(at)his(dot)de>
To: <pgsql-hackers(at)postgresql(dot)org>
Sent: Tuesday, June 22, 2004 11:50 AM
Subject: [HACKERS] User Privileges using dblink


Hello,

we want use dblink to connect several databases in a client/server
environment. Connection from local users to the remote databases should be
possible only for privileged users. We tried a solution with dblink,
embedding this command in a view, like this:

create view inst as select * from dblink('host=pollux port=5432
dbname=cob_int user=his_int password=#integration#', .....

This solution is insecure, because login and password is readable for
everyone.

We tried to call dblink without username and login, but it fails,i.e.

 create view inst as select * from dblink('host=pollux port=5432
dbname=cob_int', .....

What we are searching for, is a solution which uses the current login
information (user and password).


The second problem with dblink is a security hole. If you have a table
without any grants for the current user, this user can create a view to
circumvent the table privileges, i.e..

Current user is svawork (not a superuser!). Current database is sva4_int1.
Table inst has privileges only for a user sva. If user svawork tried to read
from inst it fails. This is ok.
If svawork create a view like:

create view myinst as select * from dblink('dbname=sva4_int1','select ....
from inst') as (.......);

The view connect not to a remote database. It uses the local database.
You can read the data from table inst without any restrictions! (Select *
from myinst ...)
This problem could also be resolved, if dblink uses the current login
information.

Any solutions welcome.

Karsten




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