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

[David Kupka]

On 01/09/15 16:53, Simo Sorce wrote:
> 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.

Or as Honza pointed out we can use case-insensitive search like this: 
(krbPrincipalName:caseIgnoreMatch:=ADMIN at EXAMPLE.COM). This will return 
all variants of casing and reduce the need for fallback code.

>
> 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.
>
-- 
David Kupka