Horton

Re: Postgres 11 release notes

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Bruce Momjian <bruce@momjian.us>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-05-14T23:10:20Z
Lists: pgsql-hackers 
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.

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

> 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.

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

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.