> On Jul 23, 2021, at 6:22 AM, Robert Haas <robertmhaas@gmail.com> wrote:
>
> And I think that's a good illustration of why it's a bad idea to
> categorize things according to whether or not they have a certain
> consequence.
Well, one very big reason for wanting to break superuser into separate roles is to make postgres-as-a-service providers
comfortablegranting more privileges to customers. If we design any privilege escalations into one of those roles, then
nosensible service provider is ever going to grant it to anybody, which fairly much defeats the purpose of this work.
Theprivilege escalations we need to prevent are not just escalations to superuser, but also escalations to other
privilegedroles. Contrary to this design goal, the "pg_host_security" role is a bit of a synonym for "superuser",
sincebeing able to write files or execute shell commands is a path to superuser, and we can't do too much about that.
"pg_database_security","pg_network_security", and "pg_logical_replication" are not synonyms for "superuser".
I like your idea of designing some extra security around event triggers to resolve their privilege escalation problems.
A GUC seems the wrong approach to me.
I think a superuser-only GUC to suppress firing event triggers won't quite cut it, because the other privileged roles
wouldstill be in danger of being trapped by a clever pg_database_security event trigger author; but extending
permissionson the GUC to include the other roles would mean that they, and not just superuser, could evade event
triggerbased auditing solutions. That is odd, because you wouldn't expect granting pg_network_security or
pg_logical_replicationto have anything to do with granting privilege to defeat audit logging.
A superuser-only GUC for this is also a bit too heavy handed. The superuser may not want to circumvent all event
triggers,just those put in place by the pg_database_security role. If that sounds arbitrary, just consider the
postgres-as-a-servicecase. The superuser wants to be able to grant pg_database_security to the customer, but doesn't
wantthe customer to be able to use that to trap the service provider.
Instead of a GUC, how about checking permissions inside event triggers for both the user firing the trigger *and* the
triggerowner. That's a backward compatibility break, but maybe not a bad one, since until now only superusers have
beenallowed to create event triggers. Systems which create an event trigger using a role that later has superuser
revoked,or which change ownership to a non-superuser, will see a behavior change. I'm not super happy with that, but I
thinkit is better than the GUC based solution. Event triggers owned by a superuser continue to work as they do now.
Eventtriggers owned by a non-superuser cannot be used to force a privileged user to run a command that the event
triggerowner could not have run for themself.
—
Mark Dilger
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
