Re: Authentication failures on a RHEL 9.2 IPA server

[Charles Hedrick]

I got my test servers working properly. But when I did my first production server, I ran
into problems that might affect others:

Unlike the test, for the primary migration I wanted to generate SIDs before doing the
upgrade, to minimize downtime after the upgrade. In testing, I used "ipa config-mod
--add-sids --enable-sid" on an upgraded (RHEL 9.2) server. It worked fine once I got
the  necessary idranges set up. However on the production service "ipa config-mod
--add-sids --enable-sid" was done under RHEL 9.0 with IPA 4.9.8. It gave an error
when there was a UID and GID with the same numeric value. In the new version, it used the
secondary SID, but not always with the old version. I had to set the SIDs manually in some
cases.

This is simply a warning for people trying the same thing. Error messages occur in
/var/log/dirserv/.../errors. There's no sign from the command line of any problems.

________________________________
From: Charles Hedrick via FreeIPA-users <freeipa-users(a)lists.fedorahosted.org&gt;
Sent: Monday, May 15, 2023 4:33 PM
To: Rob Crittenden <rcritten(a)redhat.com>; FreeIPA users list
<freeipa-users(a)lists.fedorahosted.org&gt;
Cc: Sam Morris <sam(a)robots.org.uk>; Alexander Bokovoy <abokovoy(a)redhat.com>;
Charles Hedrick <hedrick(a)rutgers.edu&gt;
Subject: [Freeipa-users] Re: Authentication failures on a RHEL 9.2 IPA server

ipa id-range-find didn't find the ranges on the other servers after I added them on
one. It found the primary ranges (managed by ipa-replica-manage) on all 3 systems, but of
course they are different.

________________________________
From: Rob Crittenden <rcritten(a)redhat.com&gt;
Sent: Monday, May 15, 2023 4:15 PM
To: FreeIPA users list <freeipa-users(a)lists.fedorahosted.org&gt;
Cc: Sam Morris <sam(a)robots.org.uk>; Alexander Bokovoy <abokovoy(a)redhat.com>;
Charles Hedrick <hedrick(a)rutgers.edu&gt;
Subject: Re: [Freeipa-users] Re: Authentication failures on a RHEL 9.2 IPA server

Charles Hedrick via FreeIPA-users wrote:
>  OK, so I see the answer to my problem is to run
>
>  ipa config-mod --add-sids --enable-sid
>
>  But we have old UIDs that with low numbers. It looks like I need to do
>
>  ipa idrange-add CS.RUTGERS.EDU_low_id_range --base-id=1
>  --range-size=200000 --rid-base=200000000 --secondary-rid-base=300000000
>  ipa idrange-add CS.RUTGERS.EDU_mid_id_range --base-id=600000
>  --range-size=200000 --rid-base=400000000  --secondary-rid-base=500000000
>
>  In order for ipa user-add for those UIDs to work on any system,
>  presumably I have to do that on all IPA servers. Is that OK? I'm
>  assuming new id's where we don't specify a UID will be put in the same
>  range before, which is different on each server. 
Ranges are global, not per-server. So assuming your ranges are ok and
there are no overlaps for the IDs or RID ranges this is probably ok, but
I'm not a PAC expert.

I think what you're seeing is the DNA  (Distributed Numeric Assignment)
plugin at work.

On the first installed server, DNA has the full range of id_range values
to generate UIDs and GIDs. The first time a replica needs to generate a
UID/GID it requests a range and gets half of the allocation. A replica
does not automatically get a range on install. The more servers you have
AND the more replicas you've added entries on, the smaller the available
ranges may be. You can use ipa-replica-manage to display and manipulate
the ranges.

rob

>  ------------------------------------------------------------------------
>  *From:* Sam Morris via FreeIPA-users <freeipa-users(a)lists.fedorahosted.org&gt;
>  *Sent:* Monday, May 15, 2023 8:08 AM
>  *To:* FreeIPA users list <freeipa-users(a)lists.fedorahosted.org&gt;
>  *Cc:* Alexander Bokovoy <abokovoy(a)redhat.com>; Sam Morris
>  <sam(a)robots.org.uk&gt;
>  *Subject:* [Freeipa-users] Re: Authentication failures on a RHEL 9.2 IPA
>  server
>
>  On Mon, May 15, 2023 at 09:28:22AM +0300, Alexander Bokovoy via
>  FreeIPA-users wrote:
> > On su, 14 touko 2023, Sam Morris wrote:
> > > On Fri, May 12, 2023 at 06:19:44PM +0100, Sam Morris via FreeIPA-users wrote:
> > > > I wonder about the root cause; is this because MIT Kerberos 1.20 always
> > > > wants to include a PAC in its issued TGTs, and it gives up if it can't
> > > > retrieve a user's SID from the directory? (If so I wonder if setting
> > > > disable_pac = true in the realm section of krb5.conf would have worked
> > > > around the problem?)
> > >
> > > This seems to be the case. Specifically I:
> > >
> > > 1. Removed the ipantsecurityidentifier attribute from a user, and
> > >    removed ipantuserattrs from the user's objectclass
> > > 2. Tried to log in as the user & got the same failures + 'No such file
> > >    or directory' message in /var/log/krb5kdc.log
> > > 3. Edited /var/kerberos/krb5kdc/kdc.conf, adding 'disable_pac = true'
> > >    within the realm-specific configuration in the realms section
> > > 4. Restarted krb5kdc
> > > 5. Tried to log in as the user and it worked!
> > >
> > > The docs for disable_pac say:
> > >
> > >    If true, the KDC will not issue PACs for this realm, and S4U2Self
> > >    and S4U2Proxy operations will be disabled.  The default is false,
> > >    which will permit the KDC to issue PACs.  New in release 1.20.
> > >
> > > ... which doesn't explain that if the KDC can't issue a PAC for some
> > > reason then the KDC will fail to issue the TGT. But at least I've gotten
> > > to the bottom of things now. :)
> >
> > RHEL IdM documentation has a separate chapter related to it.
> >
> > RHEL 9:
> >
> https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/9/...
> >
> > RHEL 8:
> >
> https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/...
> >
> > This documentation is in place since summer 2022.
>
>  Brilliant. It's interesting that the docs say "As of RHEL 8.6, Kerberos
>  in IdM requires that your IdM objects have SIDs, which are necessary for
>  security based on Privilege Access Certificate (PAC) information.", but
>  I had no problems with authentication on my RHEL 8.6/8.7 servers...
>
> > > > "After upgrading, krb5kdc may fail to issue TGTs to users who have
> not
> > > > had a SID assigned to their accounts ('ipa user-show user --all'
> will
> > > > not include an ipantsecurityidentifier attribute). In this case
> > > > krb5kdc.log will log a message "HANDLE_AUTHDATA: user(a)EXAMPLE.COM for
> > > > krbtgt/EXAMPLE.COM(a)EXAMPLE.COM, No such file or directory". This can
> be
> > > > fixed by running 'ipa config-mod --enable-sid --add-sids' as an
> IPA
> > > > admin on another IPA server."
> > >
> > > ... "or on the same server after temporarily setting "disable_pac =
> > > true" in kdc.conf, and restarting krb5kdc."
> >
> > You should not be disabling PAC because you are really setting yourself
> > up to an attack with a known exploit out in a wild.
>
>  Absolutely--I just wanted to document what I'd found out, because there
>  isn't a clear connection documented between the behaviour in RHEL 9.2
>  with MIT Kerberos 1.20 and the behaviour seen when your IPA users don't
>  have SIDs assigned.
>
>  --
>  Sam Morris <https://robots.org.uk/>
>  PGP: rsa4096/CAAA AA1A CA69 A83A 892B  1855 D20B 4202 5CDA 27B9
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