Horton

Re: Postgres 11 release notes

Bruce Momjian <bruce@momjian.us>

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From: Bruce Momjian <bruce@momjian.us>
To: Michael Paquier <michael@paquier.xyz>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-05-15T00:45:44Z
Lists: pgsql-hackers 
On Tue, May 15, 2018 at 08:10:20AM +0900, Michael Paquier wrote:
> On Mon, May 14, 2018 at 04:04:58PM -0400, Bruce Momjian wrote:
> > So, channel binding has had me confused since I first heard about it.  I
> > have done some research and reworded the commit with the attached
> > first patch.
> 
> pg11.diff looks roughly fine to me.
> 
> > Also, I have created a second patch which actually explains the two
> > SCRAM channel binding options and how the work.
> 
> +         The list of channel binding types supported by the server are
> +         listed in <xref linkend="sasl-authentication"/>.  An empty value
> +         specifies that the client will not use channel binding.  If this
> +         parameter is not specified, <literal>tls-unique</literal> is used,
> +         if supported by both server and client.
> 
> OK, that's simple enough for users, and we talk about the libpq
> parameter here.

Great, committed.

> The second paragraph is also a nice addition.  You really looked at this
> stuff!

Committed too.

Yeah, it bugs me when I hear terms thrown around but can't get to the
details of what is happening.  This PDF unlocked it for me:

	http://www.manulis.eu/papers/MaStDe_SSR14.pdf

> > One question I do have is how do we prevent a fake server in the middle
> > from pretending it is a PG 10 server and therefore avoiding channel
> > binding protections?  I don't see any channel binding options in
> > pg_hba.conf, and while libpq has options, they are explained with "This
> > parameter is mainly intended for protocol testing."
> 
> The answer is that you cannot do that now, as much as you cannot have a
> client forbid connection attempt if the client requests SCRAM but the
> server downgrades to MD5.  I had a topic on the matter at an unconf
> session at the last PGAsia, and except for administrators which forgot
> to upgrade a set of servers that was not something worth complicating
> the code for, at least that's the conclusion which came out of the
> session.  At the end, this is not actually something that you would
> control from the server if you care about security, but something which
> is controlled from the client.  The limitations that we have know are
> partially due to the way libpq handles the authentication protocol.
> Hence if you want to prevent servers attempting to do downgrades, you
> need options like sslmode saying those things from the client point of
> view:
> - I want SCRAM, but refuse connection request if server attempts MD5 or
> something else.
> - I want SCRAM and channel binding, but refuse connection request if
> server does not advertise channel binding to the client.

Agreed.  The libpq parameters don't help, I assume.

> There may be value to an server side parameter which forces clients to
> use channel binding even if the server has advertised the channel
> binding SASL mechanism, and even if connection is made with SSL, but
> that's not a downgrade-attack prevention.

What TLS does is to mix the offered ciphers into the negotiation hash so
a man-in-the-middle can't pretend it doesn't support something.  Could
we do something like that here?

I have to question the value of man-in-the-middle protection that is so
easily bypassed.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +

Commits

  1. doc: update PG 11 release notes

  2. Fix misspelled pg_trgm contrib name in PostgreSQL 11 release notes

  3. Doc: clarify release note text about v11's new window function features.

  4. Improve wording of release notes item

  5. Fix typos in release notes

  6. Doc: preliminary list of PG11 major features.

  7. Make numeric power() handle NaNs according to the modern POSIX spec.

  8. Various improvements of skipping index scan during vacuum technics

  9. Revert back-branch changes in power()'s behavior for NaN inputs.

  10. Avoid wrong results for power() with NaN input on more platforms.

  11. Avoid wrong results for power() with NaN input on some platforms.

  12. Skip full index scan during cleanup of B-tree indexes when possible

  13. Rewrite the code that applies scan/join targets to paths.

  14. Postpone generate_gather_paths for topmost scan/join rel.

  15. Add casts from jsonb

  16. Make plpgsql use its DTYPE_REC code paths for composite-type variables.

  17. Don't allow VACUUM VERBOSE ANALYZE VERBOSE.

  18. Pass InitPlan values to workers via Gather (Merge).

  19. Account for the effect of lossy pages when costing bitmap scans.

  20. Allow no-op GiST support functions to be omitted.

  21. Rearm statement_timeout after each executed query.

  22. Push limit through subqueries to underlying sort, where possible.