On Apr 8, 2011, at 6:17 PM, Alvaro Herrera wrote:
>> In other words, if you wrap an unprivileged operation inside of
>> privileged operations, it seems like the unprivileged operation then
>> becomes privileged. Right?
> Well, it's in the hands of the creator of the overall wrapper function
> to ensure that the before/after functions are "safe" in that sense.

How do you do that in a safe way though? The problem you run into is if you 
have a pair of operations that need to be done as a superuser, and something 
else you want to do in the middle as a non-super user. The goal here is to 
ensure that you MUST perform both operations out of the pair. The problem is: 
how do you enforce that the cleanup will actually happen?

Right now, we're doing this through a single function that performs the first 
SU action, does whatever the user asked, and then performs the second SU 
action. I don't think there's any other way to do that, at least not in 8.3.

To make this robust, you can't just provide secdef functions that wrap your 
operations that require SU: that would mean that anyone could still call them, 
which means they could potentially call the 1st operation and not the 2nd.

I suspect there might be clever ways around this issue, but ISTM that there 
should be some reasonable way to handle this.

BTW, Alvaro did some digging and discovered that the SQL spec allows you to 
drop to a lower privilege state, but then there's no way you can regain your 
higher-level privileges until the code block that requested lower privileges 
exits. That would actually work fine here, so long as you defined a 
sub-transaction (ie: an embedded BEGIN; END; block in plpgsql as a code block. 
With such a facility, you could do:

privileged operation...

  SET ROLE original_user;
  UNprivileged operation...

privileged operation...
Jim C. Nasby, Database Architect                   j...@nasby.net
512.569.9461 (cell)                         http://jim.nasby.net

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