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From: Mark Dilger <hornschnorter@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Dave Page <dpage@pgadmin.org>
Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Cc: Stephen Frost <sfrost@snowman.net>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: Monitoring roles patch
Date: Tue, 28 Mar 2017 13:36:44 -0700
Message-ID: <CA5B369D-1DA1-4269-8DB5-EEF96DCBE1D5@gmail.com> (raw)
In-Reply-To: <24603.1490732232@sss.pgh.pa.us>
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> On Mar 28, 2017, at 1:17 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> 
> Mark Dilger <hornschnorter@gmail.com> writes:
>> I don't see anything wrong with adding roles in pg_authid.h with a #define'd
>> Oid.  That's actually pretty helpful for anyone writing code against the database,
>> as they don't have to look up the Oid of the role.
> 
>> But why not then grant privileges to that role in information_schema.sql? 
> 
> To the extent that the desired privileges can be represented at the SQL
> level, I agree that that's a better solution than hard-wiring checks in C
> code.  The problem comes in with cases where that's not fine-grained
> enough.  Consider a policy like "anybody can select from pg_stat_activity,
> but unless you have privilege X, the query column should read as nulls
> except for sessions belonging to you".  That behavior can't realistically
> be represented as a separate SQL privilege.  Right now we have "privilege
> X" for this purpose hard-coded as "is superuser", but it would be much
> better if it were associated with a grantable role.

Many thanks for all the explanation.  I now understand better what the
patch is trying to do, and have (with some experimentation) seen flaws
in what I was saying upthread.  I find the notion of a role not being a
group of privileges but instead actually being a privilege confusing, and
it made it hard to think about the security implications of the proposal.
I'm accustomed to the idea of being able to revoke a privilege from a
role, and that doesn't work if the "role" is in some sense a privilege, not
a role.  I might find it all easier to think about if we named these things
privileges and not roles, like pg_read_stats_privilege instead of
pg_read_stats_role, and then we could grant pg_read_stats_privilege
to roles.  But I recall you were saying upthread that you did not want to
have privilege bits for each of these types of things.  I hope this feature
is worth the confusion it causes.

mark

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