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

Mon Aug 10 20:15:51 UTC 2015

On Mon, 10 Aug 2015, Alexander Bokovoy wrote:
>On Sun, 09 Aug 2015, Simo Sorce wrote:
>>On Fri, 2015-08-07 at 23:56 +0300, Alexander Bokovoy wrote:
>>>On Tue, 28 Jul 2015, Sumit Bose wrote:
>>>>On Tue, Jul 28, 2015 at 01:42:29PM +0200, Sumit Bose wrote:
>>>>> On Tue, Jul 28, 2015 at 02:26:34PM +0300, Alexander Bokovoy wrote:
>>>>> > 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 didn't want to use 'canonical' because the result will not be the
>>>>> canonical name in the general case but only a name we use for searching.
>>>>> I was thinking about 'normalized' bit this has a special meaning with
>>>>> unicode. So I came up with 'unify'. But if you prefer 'canon' I can
>>>>> change it.
>>>>>
>>>>> >
>>>>> > >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.
>>>>>
>>>>> ok, I will change this.
>>>>
>>>>new version with changed name and 1/2 KiB buffer attached. No changes to
>>>>the 2nd patch.
>>>Thanks.
>>>
>>>Patches look good to me. I, perhaps, would have added
>>>  char *canon_princ = NULL;
>>>
>>>in the definition of canon_princ but as you never access it in case
>>>asprintf() failed, that's fine.
>>>
>>>Simo?
>>>
>>
>>LGTM.
>Hold on. I think I've found a bug -- when krbPrincipalName values match
>insensitively but krbCanonicalName value is missing, we do not set
>principal to the matched value. This breaks canonicalization for case
>when there is only one krbPrincipalName as you don't need to have
>krbCanonicalName in this case.
>
>I have a prototype which still misses checks.
... and I think we miss checks in few other places. I'm getting
canonicalization working randomly -- sometimes one or two times in a row
I get 'Client principal is not found' for canonicalization case:

Aug 10 20:01:21 m1.example.com krb5kdc[18758](Error): searched for
admin at example.com, found admin at EXAMPLE.COM, result is 1, index is 0,
next val is (nil)

Aug 10 20:01:21 m1.example.com krb5kdc[18758](Error): searched for
krbtgt/example.com at example.com, found krbtgt/EXAMPLE.COM at EXAMPLE.COM,
result is 1, index is 0, next val is (nil)

Aug 10 20:01:21 m1.example.com krb5kdc[18758](info): AS_REQ (6 etypes
{18 17 16 23 25 26}) 192.168.122.99: NEEDED_PREAUTH: admin at example.com
for krbtgt/example.com at example.com, Additional pre-authentication
required

Aug 10 20:01:24 m1.example.com krb5kdc[18758](Error): searched for
admin at example.com, found admin at EXAMPLE.COM, result is 1, index is 0,
next val is (nil)

Aug 10 20:01:24 m1.example.com krb5kdc[18758](Error): searched for
krbtgt/example.com at example.com, found krbtgt/EXAMPLE.COM at EXAMPLE.COM,
result is 1, index is 0, next val is (nil)

Aug 10 20:01:24 m1.example.com krb5kdc[18758](info): AS_REQ (6 etypes
{18 17 16 23 25 26}) 192.168.122.99: ISSUE: authtime 1439236884, etypes
{rep=18 tkt=18 ses=18}, admin at example.com for
krbtgt/example.com at example.com

Aug 10 20:01:58 m1.example.com krb5kdc[18758](info): AS_REQ (6 etypes
{18 17 16 23 25 26}) 192.168.122.99: CLIENT_NOT_FOUND: admin at example.com
for krbtgt/example.com at example.com, Client not found in Kerberos
database

These are logs with debugging I've added.
-- 
/ Alexander Bokovoy