Re: Experiments with Postgres and SSL

On Thu, 22 Feb 2024 at 18:02, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
>
> On 22/02/2024 01:43, Matthias van de Meent wrote:
>> On Wed, 10 Jan 2024 at 09:31, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
>>> 4. The number of combinations of sslmode, gssencmode and sslnegotiation
>>> settings is scary. And we have very few tests for them.
>>
>> Yeah, it's not great. We could easily automate this better though. I
>> mean, can't we run the tests using a "cube" configuration, i.e. test
>> every combination of parameters? We would use a mapping function of
>> (psql connection parameter values -> expectations), which would be
>> along the lines of the attached pl testfile. I feel it's a bit more
>> approachable than the lists of manual option configurations, and makes
>> it a bit easier to program the logic of which connection security
>> option we should have used to connect.
>> The attached file would be a drop-in replacement; it's tested to work
>> with SSL only - without GSS - because I've been having issues getting
>> GSS working on my machine.
>
> +1 testing all combinations. I don't think the 'mapper' function
> approach in your version is much better than the original though. Maybe
> it would be better with just one 'mapper' function that contains all the
> rules, along the lines of: (This isn't valid perl, just pseudo-code)
>
> sub expected_outcome
> {
[...]
> }
>
> Or maybe a table that lists all the combinations and the expected
> outcome. Something lieke this:
[...]
>
> The problem is that there are more than two dimensions. So maybe an
> exhaustive list like this:
>
> user sslmode gssmode outcome
>
> nossluser require disable fail
> ...

> I'm just throwing around ideas here, can you experiment with different
> approaches and see what looks best?

One issue with exhaustive tables is that they would require a product
of all options to be listed, and that'd require at least 216 rows to
manage: server_ssl 2 * server_gss 2 * users 3 * client_ssl 4 *
client_gss 3 * client_ssldirect 3 = 216 different states. I think the
expected_autcome version is easier in that regard.

Attached an updated version using a single unified connection type
validator using an approach similar to yours. Note that it does fail 8
tests, all of which are attributed to the current handling of
`sslmode=require gssencmode=prefer`: right now, we allow GSS in that
case, even though the user require-d sslmode.

An alternative check that does pass tests with the code of the patch
is commented out, at lines 209-216.

>>> ALPN
>>
>> Does the TLS ALPN spec allow protocol versions in the protocol tag? It
>> would be very useful to detect clients with new capabilities at the
>> first connection, rather than having to wait for one round trip, and
>> would allow one avenue for changing the protocol version.
>
> Looking at the list of registered ALPN tags [0], I can see "http/0.9";
> "http/1.0" and "http/1.1".

Ah, nice.

> I think we'd want to changing the major
> protocol version in a way that would introduce a new roundtrip, though.

I don't think I understand what you meant here, could you correct the
sentence or expand why we want to do that?
Note that with ALPN you could negotiate postgres/3.0 or postgres/4.0
during the handshake, which could save round-trips.

Kind regards,

Matthias van de Meent
Neon (https://neon.tech)