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

[David Kupka]

On 02/09/15 14:27, Simo Sorce wrote:
> On Wed, 2015-09-02 at 08:11 +0200, David Kupka wrote:
>> 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.
>
> The principal name is not case insensitive, a search like that would
> probably cause DS to do a full search through the krbPrincipalName
> index, it might quickly become a performance issue. Before choosing a
> method please create an install with a 10000 principals, and then
> compare the speed of a few thousand search with exact matching case and
> a few with specifying caseIgnoreMatch and see the difference.
>
> Simo.

We will add index for caseIgnoreCaseIA5Match matching rule on 
krbPrincipalName and then the case insensitive match should be as quick 
as the case sensitive.

Without the index it is indeed far slower. I've generated 10k users and 
compared 100 ldapsearches: The indexed ones took ~ 4 seconds and the 
nonindexed one ~2 minutes. That's by two orders of magnitude worse.

When we tried to add the index into DS we uncovered a bug in the way DS 
handles nsMatchingRule attributes. Thierry investigated it and is 
filling the ticket for DS right now. Thierry can you please send link?

Once it's fixed we should be good.

David

>
>>> 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