ROLE INHERIT

David Legault wrote:

Hello,

I'm a bit new to Postgre, and I'm experimenting with the roles stuff.

I want to know why If I create a role called "administrator" (a group
basically, no login) :

CREATE ROLE administrator NOSUPERUSER INHERIT NOCREATEDB CREATEROLE;

And then create a user

CREATE ROLE admin LOGIN PASSWORD 'password' ON ROLE administrator;

admin doesn't have the CREATEROLE privilege himself, but because he is
part of a group that has it, why doesn't this fall back on him having it?

When I try to use that admin user to create another role, it says
insufficient privileges.

Am I missing something in this role stuff ?

Thanks

David

Doesn't the inherit property need to be on the role that will do the
inheriting? I.e. if admin is to inherit the privileges of administrator,
then admin needs the inherit property.

"A role with the INHERIT attribute can automatically use whatever
database privileges have been granted to all roles it is directly or
indirectly a member of."

--
Paul Lambert
Database Administrator
AutoLedgers

David Legault escribi�:

Hello,

I'm a bit new to Postgre, and I'm experimenting with the roles stuff.

I want to know why If I create a role called "administrator" (a group
basically, no login) :

CREATE ROLE administrator NOSUPERUSER INHERIT NOCREATEDB CREATEROLE;

And then create a user

CREATE ROLE admin LOGIN PASSWORD 'password' ON ROLE administrator;

admin doesn't have the CREATEROLE privilege himself, but because he is part
of a group that has it, why doesn't this fall back on him having it?

When I try to use that admin user to create another role, it says
insufficient privileges.

Am I missing something in this role stuff ?

A single point, which is that while the privileges that are inherited
are those that you can GRANT and REVOKE with the respective commands.
CREATEROLE and the others are not inherited.

Also, keep in mind that while role "admin" does not have CREATEDB
privilege, if you grant it the CREATEROLE privilege it will easily be
able to create a database by creating another role with CREATEDB
privilege. So don't grant CREATEROLE to just anyone.

FYI, the short name of PostgreSQL is "Postgres", not Postgre.

--
Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

The docs should probably be more clear about this because you can do:

GRANT *role* [, ...] TO *username* [, ...] [ WITH ADMIN OPTION ]

GRANT on Roles

This variant of the GRANT command grants membership in a role to one or more
other roles. Membership in a role is significant because it conveys the
privileges granted to a role to each of its members.
GRANT administrator TO admin;

I thought it would transfer that CREATEROLE privilege too.

Thanks

David

"David Legault" <legault.david@gmail.com> writes:

I thought it would transfer that CREATEROLE privilege too.

This is documented someplace ... ah, under CREATE ROLE:

: The INHERIT attribute governs inheritance of grantable privileges (that
: is, access privileges for database objects and role memberships). It
: does not apply to the special role attributes set by CREATE ROLE and
: ALTER ROLE. For example, being a member of a role with CREATEDB
: privilege does not immediately grant the ability to create databases,
: even if INHERIT is set; it would be necessary to become that role via
: SET ROLE before creating a database.

The main reason we did that is that SUPERUSER seemed a bit too dangerous
to be an inheritable privilege. You could argue the other role
attribute bits either way, but for simplicity they all act the same.

regards, tom lane

Tom Lane wrote:

"David Legault" <legault.david@gmail.com> writes:

I thought it would transfer that CREATEROLE privilege too.

I've been dying to get 2 cents in on this. Tell me if this suggestion
makes any sense.

We use real database users in our systems, we don't connect in with an
over-endowed user and then arbitrate security in client code.
Therefore, we depend entirely upon the server's ability to enforce security.

The practical advantage of this, which is huge, is that nowhere in my
Postgres settings do I have to make allowance for the web user (apache)
to "go root" with respect to Postgres. As a general rule we consider
this good of course, because a remote exploit on the web server could
not do anything the user could not do anyway.

Except for the hole. On a public site that lets users register, we have
to have way to let the web server assume the role of somebody who has
createuser privelege, and that's pretty much the end of the no-root
policy. If an exploit could be placed, it could simply go into that
mode and create a superuser.

What would be really nice is if you could limit the ability of
CREATEUSER to grant roles. A nice general solution would be to allow a
user with CREATEUSER privelege to only put other users into the same
groups that person is in, or perhaps into a list specified by a
higher-privelege user.

What's chances of anything like that showing up?

And, dumb question, am I mistaking the purpose of INHERIT and it already
does what I'm saying? I don't think so because INHERIT does not let
somebody create users out of the void.

Well basically, I was planning on building my user accounts directly using
the postgres user/group policy and get away from the model superuser always
connects to the DB.

I kind of think it defeats the purpose of inheritance of attributes if you
can't inherit from all attributes of a certain group.

basically, you have a web app with a guest account into a guests group for
any anonymous user that comes in. Once they log in, they have access to
their privileges. If an "administrator" group user logs in I want him to be
able to add "sub-admin" people and administer the users/groups via an admin
web interface. Since my application is built in modules, all web application
privileges (usually page/action combo) are correlated with the group
privileges (which determine which stored proc/functions) that person has
access via his membership to the groups.

The way I see it , is just an extra loop for me. When I create a new user
and assign him a group, I'll simply check if any of the group membership he
has contains the CREATEROLE and just give it to him and vice-versa if he
loses a group and doesn't have it anymore.

Could there be an option (off by default) that could tell Postgres to
INHERIT those 4 conditions like the command:

GRANT *role* [, ...] TO *username* [, ...] [ WITH [ADMIN OPTION] [FULL
INHERIT] ]

Or something similar.

Thanks

David

Kenneth Downs <ken@secdat.com> writes:

Except for the hole. On a public site that lets users register, we have
to have way to let the web server assume the role of somebody who has
createuser privelege, and that's pretty much the end of the no-root
policy. If an exploit could be placed, it could simply go into that
mode and create a superuser.

What would be really nice is if you could limit the ability of
CREATEUSER to grant roles.

I believe that a role that has CREATEROLE but not SUPERUSER can only
create non-SUPERUSER roles. Does that help?

regards, tom lane

Tom Lane wrote:

Kenneth Downs <ken@secdat.com> writes:

Except for the hole. On a public site that lets users register, we have
to have way to let the web server assume the role of somebody who has
createuser privelege, and that's pretty much the end of the no-root
policy. If an exploit could be placed, it could simply go into that
mode and create a superuser.

What would be really nice is if you could limit the ability of
CREATEUSER to grant roles.

I believe that a role that has CREATEROLE but not SUPERUSER can only
create non-SUPERUSER roles. Does that help?

regards, tom lane

Probably not. The problem is that a person with createrole can create
any role, so by mistake or exploit a user can be given admin access
(admin here defined by roles given, not by SUPERUSER flag) to another
database by a role that itself is supposed to be a public-only mostly
read-only role.

* Kenneth Downs (ken@secdat.com) wrote:

We use real database users in our systems, we don't connect in with an
over-endowed user and then arbitrate security in client code.
Therefore, we depend entirely upon the server's ability to enforce security.

We do the same thing. :)

The practical advantage of this, which is huge, is that nowhere in my
Postgres settings do I have to make allowance for the web user (apache)
to "go root" with respect to Postgres. As a general rule we consider
this good of course, because a remote exploit on the web server could
not do anything the user could not do anyway.

Right, exactly.

Except for the hole. On a public site that lets users register, we have
to have way to let the web server assume the role of somebody who has
createuser privelege, and that's pretty much the end of the no-root
policy. If an exploit could be placed, it could simply go into that
mode and create a superuser.

Thankfully we don't have any systems with this requirement. :) But, a
possible solution might be to create an OOB mechanism by which you can
only pass a username/pw/whatever is needed to create a user. ie: dump
it into a file that's checked using cron or something like that. Then
another process (the cronjob, or what have you) is privileged and can
create the user on your behalf. You have to be very careful in
programming the privleged job but ideally the worst an attacker could do
would be to create additional users within whatever the normal
constraints are (which, theoretically, is something they can do from the
website *anyway*).

What would be really nice is if you could limit the ability of
CREATEUSER to grant roles. A nice general solution would be to allow a
user with CREATEUSER privelege to only put other users into the same
groups that person is in, or perhaps into a list specified by a
higher-privelege user.

What's chances of anything like that showing up?

Honestly, I think the above approach would be better than having
something in the database to try and do that...

Thanks,

Stephen