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Re: [GENERAL] column-level update privs + lock table

From: KaiGai Kohei <kaigai(at)ak(dot)jp(dot)nec(dot)com>
To: Simon Riggs <simon(at)2ndQuadrant(dot)com>
Cc: Josh Kupershmidt <schmiddy(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [GENERAL] column-level update privs + lock table
Date: 2010-12-01 03:59:46
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-generalpgsql-hackers
(2010/11/30 21:26), Simon Riggs wrote:
> On Mon, 2010-11-29 at 21:37 -0500, Josh Kupershmidt wrote:
>> I still see little reason to make LOCK TABLE permissions different for
>> column-level vs. table-level UPDATE privileges
> Agreed.
> This is the crux of the debate. Why should this inconsistency be allowed
> to continue?
> Are there covert channel issues here, KaiGai?
Existing database privilege mechanism (and SELinux, etc...) is not designed
to handle covert channel attacks, basically.
For example, if a user session with column-level UPDATE privilege tries
to update a certain column for each seconds depending on the contents of
other table X, other session can probably know the contents of table X
using iteration of LOCK command without SELECT permission.
It is a typical timing channel attack, but it is not a problem that we
should try to tackle, is it?

Sorry, I don't have a credible idea to solve this inconsistency right now.

KaiGai Kohei <kaigai(at)ak(dot)jp(dot)nec(dot)com>

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