[Freeipa-devel] [PATCH 0002] Port from python-krbV to python-gssapi

[Simo Sorce]

On Fri, 2015-08-21 at 15:52 +0200, Michael Šimáček wrote:
> 
> On 2015-08-20 20:42, Robbie Harwood wrote:
> > Michael Šimáček <msimacek at redhat.com> writes:
> >
> >> On 2015-08-20 12:32, Michael Šimáček wrote:
> >>
> >>>>>> Michael Šimáček <msimacek at redhat.com> writes:
> >>>>>>
> >>>>>>> Attaching new revision of the patch. Changes from the previous:
> >>>>>>> - ldap2's connect now chooses the bind type same way as in ipaldap
> >>>>>>> - get_default_realm usages replaced by api.env.realm
> >>>>>>> - fixed missing third kinit attempt in trust-fetch-domains
> >>>>>>> - removed rewrapping gssapi errors to ccache errors in krb_utils
> >>>>>>> - updated some parts of exception handling
> >>>
> >>> Rebased on top of current master.
> >>
> >> One of the commits reintroduced krbV dependency that I didn't notice.
> >> Attaching updated revision. Only changes against previous revision are
> >> in files daemons/dnssec/ipa-dnskeysync-replica and
> >> daemons/dnssec/ipa-ods-exporter.
> >
> > This is much better, thanks!  I've got some comments inline.
> >
> >> +except gssapi.exceptions.GSSError:
> >>       # If there was failure on using keytab, assume it is stale and retrieve again
> >>       retrieve_keytab(api, ccache_name, oneway_keytab_name, oneway_principal)
> >
> > This code still bothers me a bit, but I think fixing it is probably
> > beyond the scope of a python-gssapi port.
> 
> The code catches all GSSAPI exceptions and retries to do the same thing 
> with different keytab. So if there was a problem unrelated to keytab, 
> the same exception will be raised again. Nothing will be ignored silently.
> 
> >
> >> +    try:
> >> +        creds = get_credentials(name=name, ccache_name=ccache_name)
> >> +        # property access would raise exception if expired
> >> +        if creds.lifetime > 0:
> >> +            return creds
> >> +    except gssapi.exceptions.ExpiredCredentialsError:
> >> +        return None
> >
> > Per rfc2744, lifetime is unsigned.  It's not immediately clear what will
> > happen when `creds.lifetime == 0`; perhaps an explicit `return Nune` in
> > that case?
> 
> I think the check is probably redundant, gssapi raises exception upon 
> inquiring expired credentials. In trust-fetch-domains I just access the 
> lifetime in try-except without using the value, so I could do the same 
> here. It would be nice if gssapi provided some 'is_valid' or 
> 'is_expired' method, so I wouldn't need to rely on side-effects of 
> property access, which is hard to read and confuses pylint.

Inquiring the credentials *is* the method to check if they are valid or
expired, what don't you like about it? The fact it raises when they are
expired ?

> >
> >>           # Setup LDAP connection
> >>           try:
> >> -            ctx = krbV.default_context()
> >> -            ccache = ctx.default_ccache()
> >> -            api.Backend.ldap2.connect(ccache)
> >> +            api.Backend.ldap2.connect()
> >>               cls.ldap = api.Backend.ldap2
> >> -        except krbV.Krb5Error as e:
> >> +        except gssapi.exceptions.GSSError:
> >>               sys.exit("Must have Kerberos credentials to migrate Winsync users.")
> >
> > Can you log the error here?  The other places GSSError is being caught
> > are doing a great job of either filtering-and-raising or
> > logging-and-exiting, so thanks for fixing those.
> 
> Yes, I'll update it in next revision of the patch.
> 
> >
> >> +# Ugly hack for test purposes only. GSSAPI has no way to get default ccache
> >> +# name, but we don't need it outside test server
> >> +def get_default_ccache_name():
> >> +    try:
> >> +        out = check_output(['klist'])
> >> +    except CalledProcessError:
> >> +        raise RuntimeError("Default ccache not found. Did you kinit?")
> >> +    match = re.match(r'^Ticket cache:\s*(\S+)', out)
> >> +    if not match:
> >> +        raise RuntimeError("Cannot obtain ccache name")
> >> +    return match.group(1)
> >
> > Yup, this is still ugly.  Ah well, it's only test code.
> >
> 
> I was trying to modify the code to not need the variable and just use 
> the default, but it is used for manipulating it as a file - in 
> production it is always defined by mod_auth_gssapi. So I'd keep this as is.

Ideally we use export_cred/store_cred and not manipulate files directly,
but with memcache in the picture we have to compromise anyway, oh
well ...

Simo.


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