From: Tom Lane <tgl@sss.pgh.pa.us>
To: dennisr@visi.com <dennisr@visi.com>
Cc: pgsql-admin@postgresql.org, Scott Whitney <scott@journyx.com>
Subject: Re: Are dns CNAME's allowed or useable in pg_hba.conf hostname specification
Date: Mon, 05 Dec 2016 18:15:12 -0500
Message-ID: <3120.1480979712@sss.pgh.pa.us> (raw)
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"dennisr@visi.com" <dennisr@visi.com> writes:
> Thanks for the quick reply. Here’s some details on how we have things configured.
> We are using RHEL 7.3, the DNS names below have been changed to protect the innocent or not so innocent depending on your point of view.
> If I do a nslookup on the database host against the following CNAME some-cname-host.example.com <http://some-cname-host.example.com/; I get:
> $> nslookup some-cname-host.example.com <http://some-cname-host.example.com/;
> Server: 10.97.40.215
> Address: 10.97.40.215#53
> some-cname-host.example.com canonical name = canonical-host-name.example.com.
> Name: canonical-host-name.example.com
> Address: 10.65.160.213
> When I do the reverse lookup on the IP address return above I get the following:
> $> nslookup 10.65.160.213
> Server: 10.97.40.215
> Address: 10.97.40.215#53
> 213.160.65.10.in-addr.arpa name = canonical-host-name.example.com.
Given that, what you would have to put in pg_hba.conf is
canonical-host-name.example.com (and that needs to forward-resolve to
10.65.160.213, and possibly other addresses as well). This cross-check
is meant to prevent getting into a PG server by means of a faked
reverse-DNS entry.
(If you're wondering why we don't simply accept anything that
some-cname-host.example.com forward-maps to, it's for performance reasons:
that would require resolving every DNS name in pg_hba.conf to see if it
matches, which could be pretty awful with long pg_hba.conf files.)
regards, tom lane
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To: pgsql-admin@postgresql.org
Cc: tgl@sss.pgh.pa.us, dennisr@visi.com, scott@journyx.com
Subject: Re: Are dns CNAME's allowed or useable in pg_hba.conf hostname specification
In-Reply-To: <3120.1480979712@sss.pgh.pa.us>
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