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

[Simo Sorce]

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.

Simo.

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