[Freeipa-devel] [PATCH 0179] Preserve user principal aliases during rename operation

Wed Jul 13 12:39:56 UTC 2016

On Wed, 2016-07-13 at 13:53 +0200, Martin Babinsky wrote:
> 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 <mbabinsk at 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..e4288a5a131157815
> > > > > > ffb2
> > > > > > 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#Manag
> > > > emen
> > > > 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.

I have your same concerns in general, but the behavior change ?
I am concerned is the default preservation of the previous name.
The current code does not preserve anything, if you rename the old name
is gone. Do we think someone may depend on this behavior today ?

Aliases are less of a concern because they are new and introduced in
this version, so what behavior they'll have on rename is something we
can decide now.

The additional consideration is that on rename, with thye current
patch, a user gain an alias, what do we do if --remove-aliases=True is
set ?

Simo.