Re: ssl passphrase callback

From: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
To: Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>, Magnus Hagander <magnus(at)hagander(dot)net>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: ssl passphrase callback
Date: 2019-11-14 16:52:50
Message-ID: 20191114165250.iqjj5qkrakwwz7f2@development
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On Thu, Nov 14, 2019 at 11:34:24AM -0500, Andrew Dunstan wrote:
>On 11/14/19 11:07 AM, Bruce Momjian wrote:
>> On Thu, Nov 14, 2019 at 11:42:05AM +0100, Magnus Hagander wrote:
>>> On Wed, Nov 13, 2019 at 9:23 PM Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
>>> I think it would be beneficial to explain why shared object is more
>>> secure than an OS command. Perhaps it's common knowledge, but it's not
>>> quite obvious to me.
>>> Yeah, that probably wouldn't hurt. It's also securely passing from more than
>>> one perspective -- both from the "cannot be eavesdropped" (like putting the
>>> password on the commandline for example) and the requirement for escaping.
>> I think a bigger issue is that if you want to give people the option of
>> using a shell command or a shared object, and if you use two commands to
>> control it, it isn't clear what happens if both are defined. By using
>> some character prefix to control if a shared object is used, you can use
>> a single variable and there is no confusion over having two variables
>> and their conflicting behavior.
>I'm  not sure how that would work in the present instance. The shared
>preloaded module installs a function and defines the params it wants. If
>we somehow unify the params with ssl_passphrase_command that could look
>icky, and the module would have to parse the settings string. That's not
>a problem for the sample module which only needs one param, but it will
>be for other more complex implementations.
>I'm quite open to suggestions, but I want things to be tolerably clean.

I agree it's better to have two separate GUCs - one for command, one for
shared object, and documented order of precedence. I suppose we may log
a warning when both are specified, or perhaps "reset" the value with
lower order of precedence.


Tomas Vondra
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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