Re: Direct SSL connection with ALPN and HBA rules

On Mon, Apr 29, 2024 at 1:38 AM Heikki Linnakangas <hlinnaka@iki.fi> wrote:
> Sure, we'd try to fix them ASAP. But we've had the SSLRequest
> negotiation since time immemorial. If a new vulnerability is found, it's
> unlikely that we'd need to disable the SSLRequest negotiation altogether
> to fix it. We'd be in serious trouble with back-branches in that case.
> There's no sudden need to have a kill-switch for it.

I'm not really arguing that you'd need the kill switch to fix a
problem in the code. (At least, I'm not arguing that in this thread; I
reserve the right to argue that in the future. :D) But between the
point of time that a vulnerability is announced and a user has
upgraded, it's really nice to have a switch as a mitigation. Even
better if it's server-side, because then the DBA can protect all their
clients without requiring action on their part.

> Taking that to the extreme, you could argue for a kill-switch for every
> feature, just in case there's a vulnerability in them. I agree that
> authentication is more sensitive so reducing the surface of that is more
> reasonable. And but nevertheless.

I mean... that would be extreme, yeah. I don't think anyone's proposed that.

> If you only
> have v17 servers in your environment, so you know all servers support
> direct negotiation if they support SSL at all, but a mix of servers with
> and without SSL, sslnegotiation=directonly would reduce roundtrips with
> sslmode=prefer.

But if you're in that situation, what does the use of directonly give
you over `sslnegotiation=direct`? You already know that servers
support direct, so there's no additional performance penalty from the
less strict mode.

> Making requiredirect to imply sslmode=require, or error out unless you
> also set sslmode=require, feels like a cavalier way of forcing SSL. We
> should have a serious discussion on making sslmode=require the default
> instead. That would be a more direct way of nudging people to use SSL.
> It would cause a lot of breakage, but it would also be a big improvement
> to security.
>
> Consider how sslnegotiation=requiredirect/directonly would feel, if we
> made sslmode=require the default. If you explicitly set "sslmode=prefer"
> or "sslmode=disable", it would be annoying if you would also need to
> remove "sslnegotiation=requiredirect" from your connection string.

That's similar to how sslrootcert=system already works. To me, it
feels great, because I don't have to worry about nonsensical
combinations (with the exception of GSS, which we've touched on
above). libpq complains loudly if I try to shoot myself in the foot,
and if I'm using sslrootcert=system then it's a pretty clear signal
that I care more about security than the temporary inconvenience of
editing my connection string for one weird server that doesn't use SSL
for some reason.

> I think the best way forward for those is something like a new
> "require_proto" parameter that you suggested upthread. Perhaps call it
> "encryption", with options "none", "ssl", "gss" so that you can provide
> multiple options and libpq will try them in the order specified. For
> example:
>
> encryption=none
> encryption=ssl, none  # like sslmode=prefer
> encryption=gss
> encryption=gss, ssl   # try GSS first, then SSL
> encryption=ssl, gss   # try SSL first, then GSS
>
> This would make gssencmode and sslmode=disable/allow/prefer/require
> settings obsolete. sslmode would stil be needed to distinguish between
> verify-ca/verify-full though. But sslnegotiation would be still
> orthogonal to that.

I will give this some more thought.

Thanks,
--Jacob