[Freeipa-devel] [PATCH 149] IPA KDB: allow case in-sensitive realm in AS request

[Alexander Bokovoy]

On Tue, 28 Jul 2015, Simo Sorce wrote:
>On Tue, 2015-07-28 at 12:15 +0200, Sumit Bose wrote:
>> On Wed, Jul 22, 2015 at 09:41:51AM -0400, Simo Sorce wrote:
>> > ----- Original Message -----
>> > > From: "Sumit Bose" <sbose at redhat.com>
>> > > To: "freeipa-devel" <freeipa-devel at redhat.com>
>> > > Sent: Tuesday, July 21, 2015 7:41:14 AM
>> > > Subject: [Freeipa-devel] [PATCH 149] IPA KDB: allow case in-sensitive realm	in AS request
>> > >
>> > > Hi,
>> > >
>> > > this patch is my suggestion to solve
>> > > https://fedorahosted.org/freeipa/ticket/4844 .
>> > >
>> > > The original issue in the ticket has two part. One is a loop in libkrb5
>> > > which is already fixed. The other is to handle canonicalization better.
>> >
>> > Sorry Sumit,
>> > I see several issues with this patck.
>> >
>> > first of all you should really not change ipadb_get_principal(), that's the
>> > wrong place to apply your logic.
>> >
>> > To support searching for the realm name case-insensitively all we should do
>> > is to always forcibly upper case the realm name at the same time we build the
>> > filter (in ipadb_fetch_principals(), if canonicalization was requested.
>> > Because we will never store (code to prevent that should probably be dded with
>> > this patch) a realm name that is not all caps.
>> > Then the post search matches should be done straight within ipadb_find_principal().
>> >
>> > > The general way to allow canonicalization on a principal is to add the
>> > > attributes 'krbcanonicalname'[1] and 'ipakrbprincipalalias' together
>> > > with the objectclass 'ipaKrbPrincipal' to the user object.
>> >
>> > We have already a ticket open since long to remove krbprincipalalias, it was
>> > a mistake to add it and any patch that depends on it will be nacked by me.
>> > We need to use krbPrincipalName and krbCanonicalName.
>> >
>> > > Then the IPA
>> > > KDB backend will use 'ipakrbprincipalalias' for case in-sensitive
>> > > matches and  the principal from 'krbcanonicalname' will be the canonical
>> > > principal used further on. The 'krbPrincipalName' is not suitable for
>> > > either because it has caseExact* matching rules and is a multivalue
>> > > attribute [2].
>> >
>> > Case-exact match is a problem only if we do not canonicalize names when storing
>> > them, otherwise all you need to do is store a "search form" in krbPrincipalName
>> > and always change searches to that form (forcibly upper case realm, forcibly
>> > lowercase components) when canonicalization is requested.
>> >
>> > Additionally in the patch you are using stcasecmp(), that function is not
>> > acceptable, look at ipadb_find_principal() and you'll see we use ulc_casecmp()
>> > there.
>> > Also modyfing the principal before searching is done wrong (you use strchr()
>> > to find the @ sign, but you could find an @ in the components this way, you
>> > should use strrchr() at the very least), and is dangerous if done outside of
>> > the inner functions because then we never have a way to know the original
>> > form should it be needed. In any case as said above realm should be forcibly
>> > uppercase, given a flag in the escape function instead.
>>
>> Thank for for the review and the comments.
>>
>> I changed the patch as you suggested to upper-case the realm in the
>> escape function if the flag is set.
>>
>> I didn't add any checks to make sure that the realm of newly added
>> principal attributes is always upper case. Since the attributes can be
>> added via various ways I think the check should happen on the DS level
>
>We should indeed intercept add/modify operations and see if they try to
>set krbPrincipalName/krbCanonicalName and then validate the name.
>Return unwilling to perform if the case of the realm is different (or
>fix it on the fly, up for discussion) from the default case as
>configured in the server.
Will break trusts -- ipasam does add these principals for krbtgt/IPA at AD.

>> but I see this more in the context of full canonicalization fix covered
>> by https://fedorahosted.org/freeipa/ticket/3864 . If you think this is a
>> requirement for the patch attached I would suggest to drop
>> https://fedorahosted.org/freeipa/ticket/4844 and solve it together with
>> #3864.
>
>We should clsoe 4844 as fixed upstream (there *was* a bug in libkrb5).
>I commented on #3864 about what we can do, and we can also avoid
>changing the schema.
Yep.

>So on the new patches, what does "unify" means ? I do not get what it
>means (so probably it is a poor name), I guess you may want to call it
>"canonicalization" ? (or even 'canon' to shorten it a bit).
I have same question. I tried to understand why it is called unify and
failed.

>I think the worst case for a utf8 string is more then length*2, probably
>more like length*6, unless there is some guarantee around case changes
>that I am not aware of, that said we could probably just allocate on the
>stack a fixed size string of a KiB or so, the longest DNS name is 256
>chars IIRC and a service name can't be that much longer, also usernames
>can't be arbitrarily long. So 1/2 KiB should probably be fine for a full
>principal name. (avoids a malloc too which is good).
Yes, sounds good. A hostname label can be up to 63 characters and full
domain name including dots would be 253 characters. At the same time, a
a component of the principal may be of arbitrary length. From practical
perspective it would probably be enough to go with a static buffer of
1/2 KiB for the quickest case and fall back to malloc() if the size is
bigger than that one.


-- 
/ Alexander Bokovoy