[Fedora-directory-devel] Re: Please Review: Add LDAPI (LDAP over unix domain sockets)

[Howard Chu]

> Date: Wed, 21 Feb 2007 12:16:04 -0800
 > From: Pete Rowley <prowley at redhat.com>

Sorry, I don't mean to beat too much on a dead horse, but ...

> Howard Chu wrote:
>> > Yes. But again, the Heimdal KDC does an explicit SASL/EXTERNAL Bind to 
>> > request this privilege. There is no assumption of automagic 
>> > authorization.

> I guess we can add that. Rich and I have already talked about that as a TBD.

> While observing RFC4513 is a good thing, and this implementation does so 
> when auto-bind is switched off, I believe these kinds of decisions are 
> the domain of site administrative policy and not of standards documents. 
> Further, a client in the anonymous bind state has no practical knowledge 
> of the effects of that state on server responses in any case, nor can it 
> be sure that binding as a non-anonymous user has any effect on those 
> responses, nor indeed does auto-bind necessarily remove or add any 
> privilege for the client - that is all administrative policy and 
> undefined by any RFC. This is just one more administrative policy option.

Certainly it's true that LDAP has nothing specific to say about 
authorization. But don't confuse authorization with authentication; they're 
two separate things. A client can easily determine that it's in an anonymous 
state, using the WhoAmI extended op.

If "ldapwhoami -x -H ldapi:///" doesn't return a zero-length ID, then your 
server is broken.

> In addition, LDAP is defined as it is in no small part to the underlying 
> assumption of TCP and designed around the practical methods of 
> authentication given that assumption, strictly speaking LDAPI isn't LDAP 
> (it's not even platform agnostic), and LDAPI has other methods at its 
> disposal.

And again, don't confuse the protocol with the transport. Fuzzy thinking like 
that is one of the reasons we have LDAP today, instead of just DAP over TCP. 
Sure the RFCs only define LDAP in terms of TCP, but obviously any reliable, 
ordered, stream transport will work just as well. And in a proper library 
implementation, such a transport can be substituted between any client and 
server without needing to alter any other code in the client or server.

> While I understand your concern, the feature is an option, not a 
> requirement.

Yes, but it shouldn't be an option at all. You provide the option in the 
expectation that someone will use it. The presence of such an option 
therefore encourages client writers to depend on non-standard behaviors. You 
might say "this is a site-local policy decision" but it doesn't just affect a 
single site. You implicitly create lock-in with features like this, and you 
have no idea what other servers such clients will eventually be talking to.
I would expect thinking like this from Microsoft or Sun, but not from an open 
source developer. And no matter how much we may think our respective server 
is the best in the world, and that no one would ever have any reason to talk 
to any other server, one need only look at SunOne to see that nothing lasts 
forever. Providing options that break standards like this *hurts* your users, 
it doesn't help them.

The standard mechanism for using an LDAP session with previously established 
credentials is to use a SASL/EXTERNAL Bind. Encouraging any other behavior is 
flat out wrong.

Yes, it's OK to provide options that completely change the behavior of the 
server. But it's only OK to do that *when the client explicitly asks for it*. 
I could define a control that causes all strings to be returned in Morse 
code, and that would be perfectly fine, because a client has to use the 
control before it gets such an outlandish behavior.

Some folks may be wondering why I'm spending so much time on this point, 
since it's your server and I'm not contributing to its code. Just remember 
that network protocols are about interoperability; nothing you do exists in a 
vacuum. Every mistake anyone makes affects everyone - just look at the 
dynamic group mess if you need an example...
-- 
   -- Howard Chu
   Chief Architect, Symas Corp.  http://www.symas.com
   Director, Highland Sun        http://highlandsun.com/hyc
   Chief Architect, OpenLDAP     http://www.openldap.org/project/