Re: pgsql: Fix search_path to a safe value during maintenance operations.

On Mon, 2023-07-31 at 12:53 -0400, Robert Haas wrote:
> I agree. I think there are actually two interrelated problems here.
>
> One is that virtually all code needs to run with the originally
> intended search_path rather than some search_path chosen at another
> time and maybe by a different user. If not, it's going to break, or
> compromise security, depending on the situation. The other is that
> running arbitrary code written by somebody else as yourself is
> basically instant death, from a security perspective.

Good framing.

The search_path is a particularly nasty problem in our system because
it means that users can't even trust the code that they write
themselves! A function author has no way to know how their own function
will behave under a different search_path.

> It's a little hard to imagine a world in which these problems don't
> exist at all, but it somehow feels like the design of the system
> pushes you toward doing this stuff incorrectly rather than doing it
> correctly. For instance, you can imagine a system where when you run
> CREATE OR REPLACE FUNCTION, the prevailing search_path is captured
> and
> automatically included in proconfig.

Capturing the environment is not ideal either, in my opinion. It makes
it easy to carelessly depend on a schema that others might not have
USAGE privileges on, which would then create a runtime problem for
other callers. Also, I don't think we could just depend on the raw
search_path, we'd need to do some processing for $user, and there are
probably a few other annoyances.

It's one possibility and we don't have a lot of great options, so I
don't want to rule it out though. If nothing else it could be a
transition path to something better.

> But you can maybe imagine a system where
> all code associated with a table is run as the table owner in all
> cases, regardless of SECURITY INVOKER/DEFINER, which I think would at
> least close some holes.
>
> The difficulty is that it's a bit hard to imagine making these kinds
> of definitional changes now, because they'd probably be breaking
> changes for pretty significant numbers of users.

I believe we can get close to a good model with minimal breakage. And
when we make the problem small enough I believe other solutions will
emerge. We will probably have to hedge with some compatibility GUCs.

> But on the other
> hand, if we don't start thinking about systemic changes here, it
> feels
> like we're just playing whack-a-mole.

Exactly. If we can agree on where we're going then I think we can get
there.

Regards,
Jeff Davis