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Re: [pcp] pmlc access control, was Re: PCP Updates: qa fallout from ipv6

To: pcp@xxxxxxxxxxx
Subject: Re: [pcp] pmlc access control, was Re: PCP Updates: qa fallout from ipv6/unix sockets for pmlogger and pmlc
From: Ken McDonell <kenj@xxxxxxxxxxxxxxxx>
Date: Fri, 21 Feb 2014 08:19:21 +1100
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On 21/02/14 07:18, Frank Ch. Eigler wrote:
... I
propose pmlogger also use that information to extend the pmlogger ACL
language to assert simple predicates like

          allow unix-uidmatch : all;
          # allow unix-gidmatch : all; # probably not a good default
          allow unix : enquire;

which we could then put into the default / pmlogconf-generated files.

This looks fine to me.

As an aside, the pmlogger acl system has a nice separation of
"enquire" vs "all" operations.  However, some mutative operations are
in the enquire category, but probably shouldn't be: namely "new
volume" and "flush".  Both these could be misused for denial-of-service,
so should be restricted.

The status quo just seems wrong ... anything that can change the state of pmlogger should not be in the "enquire" class. Shall I fix this?

Locking down pmlc is unlikely to have any negative fallout.

I believe pmlc use is very rare, probably because I have not managed to convince anyone else that the "value add" proposition for pmlc in the following scenario is real:

* pmlogger configured with shallow metric coverage and long sample intervals
* pmie looking for badness
<badness happens>
* pmie rule fires to ...
        use pmlc to increase metric depth and/or reduce sample interval
        wait a while
        use pmlc to return pmlogger to default configuration

Even for this scenario, one could use a second pmlogger instance and later merge the two archives with pmlogextract, avoiding pmlc altogether.

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