[Freeipa-devel] fixing Kerberos principal aliases handling in IPA

[Simo Sorce]

On Tue, 2015-09-01 at 16:39 +0200, Martin Babinsky wrote:
> Hi list,
> 
> I own the following ticket https://fedorahosted.org/freeipa/ticket/3864 
> and I would like to clarify what needs to be done in order to make IPA 
> to fully support multiple aliases per entry.
> 
> So far I have identified these task based on the ticket comments and 
> discussion with Simo way back in the past:
> 
> 1.) mark 'ipaKrbPrincipalAlias' attribute as deprecated so that it is 
> not used in the new code.
> 
> 2.) fix ACIs that do not permit setting multiple values of 
> 'krbPrincipalName' attribute per entry (see 
> https://fedorahosted.org/freeipa/ticket/3961)
> 
> 3.) Modify KDB backend (namely 'ipadb_fetch_principal' and 
> 'ipadb_find_principal' functions) to correctly perform lookup of 
> krbprincipalname/krbcanonicalname, i.e. search krbprincipalname 
> case-insensitively and krbcanonicalname case-sensitively, return 
> krbcanonicalname when canonicalization is requested.
> 
> 4.) Modify KDB backend and IPA framework to handle creation of both 
> krbprincipalname and krbcanonicalname. I am not quite sure what cases 
> should be covered here (I remember that we should create 
> krbcanonicalname when we add another aliases to krbprincipalname), so it 
> would be nice if you could comment on this.
> 
> 5.) write tests which cover all this stuff so that we don't shoot 
> ourselves in the foot.
> 
> I am not very well versed in Kerberos so I might get some of this stuff 
> wrong. If that's the case please point me to the right direction. Also 
> please write me some additional stuff which I have fogot and needs to be 
> done.
> 

I think the summary is correct, the only thing we need to be careful is
to keep handling entries that have only a single valued krbprincipalname
correctly as that will happen in upgrade paths and potentially if
someone uses external tools.

The tricky part for point 3 is to implement it *without* changing the
schema. KrbPrincipalName is case-sensitive, however I think we can solve
the issue of "searching case-insensitively" by always lower-casing the
principal name components and always upper casing the realm part on
storage. If we always store a krbCanonicalName we get the "correct" case
there anyway so out mucking with the krbPrincipalName case will not be a
problem for any new entry.

This *may* cause issues with upgrades though, so we may need fallback
code that searches with the case sent by the client if we determine the
entry has no krbCanonicalName attribute (sign that it was created before
we started adding krbCanonicalName and never "updated").

Note that we also need to think what will happen during and upgrade when
some servers still use the current code and some servers will use the
new code. So I guess it would be nice if you could write down a table
with all possible forms a principal can be in on rows, and old/new
server states in columns, and mark what will happen for various
operations in each case.

Simo.

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