On 07/12/2016 04:19 PM, Simo Sorce wrote:
On Tue, 2016-07-12 at 15:46 +0200, Martin Babinsky wrote:
On 07/12/2016 02:00 PM, Martin Babinsky wrote:


On 07/12/2016 01:05 PM, Alexander Bokovoy wrote:

On Mon, 11 Jul 2016, Martin Babinsky wrote:

From 185bde00a76459430d95ff207bf1fb3fe31e811a Mon Sep 17
00:00:00 2001
From: Martin Babinsky <mbabi...@redhat.com>
Date: Fri, 1 Jul 2016 18:09:04 +0200
Subject: [PATCH] Preserve user principal aliases during rename
operation

When a MODRDN is performed on the user entry, the MODRDN plugin
resets
both
krbPrincipalName and krbCanonicalName to the value constructed
from
uid. In
doing so, hovewer, any principal aliases added to the
krbPrincipalName
are
wiped clean. In this patch old aliases are fetched before the
MODRDN
operation
takes place and inserted back after it is performed.

This also preserves previous user logins which can be used
further for
authentication as aliases.

https://fedorahosted.org/freeipa/ticket/6028
---
ipaserver/plugins/baseuser.py | 46
+++++++++++++++++++++++++++++++++++++++++++
1 file changed, 46 insertions(+)

diff --git a/ipaserver/plugins/baseuser.py
b/ipaserver/plugins/baseuser.py
index
0052e718afe639bcc1c0a698ded39ea8407a0551..e4288a5a131157815ffb2
452692a7edb342f6ac3

100644
--- a/ipaserver/plugins/baseuser.py
+++ b/ipaserver/plugins/baseuser.py
@@ -498,6 +498,50 @@ class baseuser_mod(LDAPUpdate):
                            len =
int(config.get('ipamaxusernamelength')[0])
                        )
                    )
+
+    def preserve_krbprincipalname_pre(self, ldap, entry_attrs,
*keys,
**options):
+        """
+        preserve user principal aliases during rename
operation. This
is the
+        pre-callback part of this. Another method called
during
post-callback
+        shall insert the principals back
+        """
+        if options.get('rename', None) is None:
+            return
+
+        try:
+            old_entry = ldap.get_entry(
+                entry_attrs.dn, attrs_list=(
+                    'krbprincipalname', 'krbcanonicalname'))
+
+            if 'krbcanonicalname' not in old_entry:
+                return
+        except errors.NotFound:
+            self.obj.handle_not_found(*keys)
+
+        self.context.krbprincipalname = old_entry.get(
+            'krbprincipalname', [])
+
+    def preserve_krbprincipalname_post(self, ldap,
entry_attrs,
**options):
+        """
+        Insert the preserved aliases back to the user entry
during
rename
+        operation
+        """
+        if options.get('rename', None) is None or not hasattr(
+                self.context, 'krbprincipalname'):
+            return
+
+        obj_pkey =
self.obj.get_primary_key_from_dn(entry_attrs.dn)
+        canonical_name = entry_attrs['krbcanonicalname'][0]
+
+        principals_to_add = tuple(p for p in
self.context.krbprincipalname if
+                                  p != canonical_name)
+
+        if principals_to_add:
+            result = self.api.Command.user_add_principal(
+                obj_pkey, principals_to_add)['result']
+
+            entry_attrs['krbprincipalname'] =
result.get('krbprincipalname', [])
+
    def check_mail(self, entry_attrs):
        if 'mail' in entry_attrs:
            entry_attrs['mail'] =
self.obj.normalize_and_validate_email(entry_attrs['mail'])
@@ -557,9 +601,11 @@ class baseuser_mod(LDAPUpdate):

        self.check_objectclass(ldap, dn, entry_attrs)
        self.obj.convert_usercertificate_pre(entry_attrs)
+        self.preserve_krbprincipalname_pre(ldap, entry_attrs,
*keys,
**options)

    def post_common_callback(self, ldap, dn, entry_attrs,
*keys,
**options):
        assert isinstance(dn, DN)
+        self.preserve_krbprincipalname_post(ldap, entry_attrs,
**options)
        if options.get('random', False):
            try:
                entry_attrs['randompassword'] =
unicode(getattr(context, 'randompassword'))
--
2.5.5

The approach looks good.

For the record, we also support aliases for hosts and service
kerberos
principals but we don't support rename options for them, so there
is no
need to add similar logic there.


That's right, I have updated the corresponding section of the
design
page [1] for future reference.

[1]
http://www.freeipa.org/page/V4/Kerberos_principal_aliases#Managemen
t_framework


Adding Simo to the loop since he is not convinced that this is the
right
behavior. As I see it, it seems to not be a security issue but more
of a
different expectations about the perceived correct behavior in this
particular situation.

I can see the use case in keeping the old aliases, e.g. keeping the
old
credentials after legal name change, but I can also see the
available
space for user principal names piling up and cluttering quickly in
large
organizations.

after some thinking I think it is ok to keep by default and then drop
as it avoid races if you do really want to keep the aliases.

However the CLI/UI should probably offer a button/switch to allow to
drop all aliases on rename, what it would do would be to modify the
entry after the rename and drop the aliases.

I am a bit uncertain what to do by default with the "original name".
I can see it going both ways on whether to keep it by default or not.

Simo.


So let me summarize the proposed behavior just to see if I understand it correctly:

1.) when the user is renamed, all his kerberos aliases are added back to the attribute after rename

2.) a new Flag will be added to *user-mod (e.g. --remove-aliases) which will suppress this behavior when True so that all previous aliases will be erased as is done now. The administrator will use this flag to override the default behavior in 1.)

We now have the following concerns:

3.) What to do with old canonical names:

The proposed patch treats old canonical names as aliases which are re-added after rename (since krbPrincipalName before rename contains the alias equal to the original canonical name anyway, we get this for free). If we implement the alias-wiping flag from 2.), we have to decide whether the old canonical name should be wiped away as well, or implement an additional logic to preserve it.

4.) What to do with users coming from pre-4.4 FreeIPA versions. These have no krbCanonicalName attribute and have only one alias = canonical name, so the code does no special handling of them and behaves as before. If we want to keep his old principal after rename, we have to implement another path which constructs krbCanonicalName attribute for him during rename and adds old principal as an alias among his krbPrincipalNames.

I would say that decoupling the preservation of old canonical principals from the preservation of aliases is relatively easy to implement, but I am bit afraid that it will increase the complexity and potential fragility of the solution.

--
Martin^3 Babinsky

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