Re: Hardening PostgreSQL via (optional) ban on local file system access

The idea is to allow superuser, but only in case you *already* have
access to the file system.
You could think of it as a two factor authentication for using superuser.

So in the simplest implementation it would be

touch $PGDATA/allow_superuser

psql
hannuk=# CREATE EXTENSION ...

rm $PGDATA/allow_superuser

and in more sophisticated implementation it could be

terminal 1:
psql
hannuk=# select pg_backend_pid();
pg_backend_pid
----------------
1749025
(1 row)

terminal 2:
echo 1749025 > $PGDATA/allow_superuser

back to terminal 1 still connected to backend with pid 1749025:
$ CREATE EXTENSION ...

.. and then clean up the sentinel file after, or just make it valid
for N minutes from creation

Cheers,
Hannu Krosing

On Wed, Jun 29, 2022 at 8:51 AM Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> wrote:
>
> On Tue, 2022-06-28 at 16:27 -0700, Andres Freund wrote:
> > > Experience shows that 99% of the time one can run PostgreSQL just fine
> > > without a superuser
> >
> > IME that's not at all true. It might not be needed interactively, but that's
> > not all the same as not being needed at all.
>
> I also disagree with that. Not having a superuser is one of the pain
> points with using a hosted database: no untrusted procedural languages,
> no untrusted extensions (unless someone hacked up PostgreSQL or provided
> a workaround akin to a SECURITY DEFINER function), etc.
>
> Yours,
> Laurenz Albe