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

On Fri, Jun 24, 2022 at 4:13 PM Andres Freund <andres(at)anarazel(dot)de> wrote:

> Hi,
>
> On 2022-06-25 00:08:13 +0200, Hannu Krosing wrote:
> > Currently the file system access is controlled via being a SUPREUSER
> > or having the pg_read_server_files, pg_write_server_files and
> > pg_execute_server_program roles. The problem with this approach is
> > that it will not stop an attacker who has managed to become the
> > PostgreSQL SUPERUSER from breaking out of the server to reading and
> > writing files and running programs in the surrounding container, VM or
> > OS.
>
> If a user has superuser rights, they automatically can execute arbitrary
> code. It's that simple. Removing roles isn't going to change that. Our code
> doesn't protect against C functions mismatching their SQL level
> definitions. With that you can do a lot of things.
>
>
Using only psql connected by the postgres role, without touching the
filesystem to bootstrap your attack, how would this be done? If you
specify CREATE FUNCTION ... LANGUAGE c you have to supply filename
references, not a code body and you won't have been able to put that code
on the server.

We should be capable of having the core server be inescapable to the
filesystem for a superuser logged in remotely. All such access they can do
with the filesystem would be mediated by controlled code/APIs.

C-based extensions would be an issue without a solution that does provide
an inescapable sandbox aside from going through our API. Which I suspect
is basically impossible given our forked process driven execution model.

David J.

David J.