[Freeipa-devel] [PATCHES 0015-0017] consolidation of various Kerberos auth methods in FreeIPA code

[Simo Sorce]

On Mon, 2015-03-23 at 14:22 +0100, Petr Spacek wrote:
> On 23.3.2015 14:08, Simo Sorce wrote:
> > On Mon, 2015-03-23 at 12:48 +0100, Martin Babinsky wrote:
> >> On 03/17/2015 06:00 PM, Simo Sorce wrote:
> >>> On Mon, 2015-03-16 at 13:30 +0100, Martin Babinsky wrote:
> >>>> On 03/16/2015 12:15 PM, Martin Kosek wrote:
> >>>>> On 03/13/2015 05:37 PM, Martin Babinsky wrote:
> >>>>>> Attaching the next iteration of patches.
> >>>>>>
> >>>>>> I have tried my best to reword the ipa-client-install man page bit about the
> >>>>>> new option. Any suggestions to further improve it are welcome.
> >>>>>>
> >>>>>> I have also slightly modified the 'kinit_keytab' function so that in Kerberos
> >>>>>> errors are reported for each attempt and the text of the last error is retained
> >>>>>> when finally raising exception.
> >>>>>
> >>>>> The approach looks very good. I think that my only concern with this patch is
> >>>>> this part:
> >>>>>
> >>>>> +            ccache.init_creds_keytab(keytab=ktab, principal=princ)
> >>>>> ...
> >>>>> +        except krbV.Krb5Error as e:
> >>>>> +            last_exc = str(e)
> >>>>> +            root_logger.debug("Attempt %d/%d: failed: %s"
> >>>>> +                              % (attempt, attempts, last_exc))
> >>>>> +            time.sleep(1)
> >>>>> +
> >>>>> +    root_logger.debug("Maximum number of attempts (%d) reached"
> >>>>> +                      % attempts)
> >>>>> +    raise StandardError("Error initializing principal %s: %s"
> >>>>> +                        % (principal, last_exc))
> >>>>>
> >>>>> The problem here is that this function will raise the super-generic
> >>>>> StandardError instead of the proper with all the context and information about
> >>>>> the error that the caller can then process.
> >>>>>
> >>>>> I think that
> >>>>>
> >>>>>       except krbV.Krb5Error as e:
> >>>>>           if attempt == max_attempts:
> >>>>>               log something
> >>>>>               raise
> >>>>>
> >>>>> would be better.
> >>>>>
> >>>>
> >>>> Yes that seems reasonable. I'm just thinking whether we should re-raise
> >>>> Krb5Error or raise ipalib.errors.KerberosError? the latter options makes
> >>>> more sense to me as we would not have to additionally import Krb5Error
> >>>> everywhere and it would also make the resulting errors more consistent.
> >>>>
> >>>> I am thinking about someting like this:
> >>>>
> >>>>       except krbV.Krb5Error as e:
> >>>>          if attempt == attempts:
> >>>>              # log that we have reaches maximum number of attempts
> >>>>              raise KerberosError(minor=str(e))
> >>>>
> >>>> What do you think?
> >>>
> >>> Are you retrying on any error ?
> >>> Please do *not* do that, if you retry many times on an error that
> >>> indicates the password is wrong you may end up locking an administrative
> >>> account. If you want to retry you should do it only for very specific
> >>> timeout errors.
> >>>
> >>> Simo.
> >>>
> >>>
> >> I have taken a look at the logs attached to the original BZ 
> >> (https://bugzilla.redhat.com/show_bug.cgi?id=1161722).
> >>
> >> In ipaclient-install.log the kinit error is:
> >>
> >> "Cannot contact any KDC for realm 'ITW.USPTO.GOV' while getting initial 
> >> credentials"
> >>
> >> which can be translated to krbV.KRB5_KDC_UNREACH error. However, 
> >> krb5kdc.log (http://pastebin.test.redhat.com/271394) reports errors 
> >> which are seemingly unrelated to the root cause (kinit timing out on 
> >> getting host TGT).
> >>
> >> Thus I'm not quite sure which errors should we chceck against in this 
> >> case, anyone care to advise? These are potential candidates:
> >>
> >> KRB5KDC_ERR_SVC_UNAVAILABLE, "A service is not available that is 
> >> required to process the request"
> >> KRB5KRB_ERR_RESPONSE_TOO_BIG,    "Response too big for UDP, retry with TCP"
> >> KRB5_REALM_UNKNOWN,      "Cannot find KDC for requested realm"
> >> KRB5_KDC_UNREACH,        "Cannot contact any KDC for requested realm"
> >>
> > 
> > The only ones that you should retry on, at first glance are
> > KRB5_KDC_UNREACH, KRB5KDC_ERR_SVC_UNAVAILABLE.
> > 
> > You should never see KRB5KRB_ERR_RESPONSE_TOO_BIG in the script as it
> > should be handled automatically by the library, and if you get
> > KRB5_REALM_UNKNOWN I do not think that retrying will make any
> > difference.
> 
> I might be wrong but I was under the impression that this feature was also for
> workarounding replication delay - service is not available / key is not
> present / something like that.
> 
> (This could happen if host/principal was added to one server but then the
> client connected to another server or so.)

If we have that problem we should instead use a temporary krb5.conf file
that lists explicitly only the server we are joining.

Simo.

-- 
Simo Sorce * Red Hat, Inc * New York