I prefer self hosted solution for some tasks. But this also means that I have to troubleshoot my problems on my own. Recently a go-ldap error gave me a headache. Here is the analysis of the protocol error – and how to solve it.
For certain projects I prefer a self hosted Git server. Solutions like Gitea, the fast developing and striving fork of Gogs, make this painless and easy to do – especially in a containerized environment.
My users are managed in a FreeIPA, and Gitea connects to it via LDAP. And this is a constant source for trouble. Gitea is written in Go, and the go ldap libraries seem to be far from perfect.
For example, after a recent update of my environment, login at Gitea stopped working:
[...gitea/models/user.go:1544 SyncExternalUsers()] [E] LDAP Search failed unexpectedly! (LDAP Result Code 2 "Protocol Error": )
The FreeIPA server at the same time showed indeed malformed requests:
 fd=112 slot=112 connection from 172.18.0.6 to 172.18.0.2  op=0 BIND dn="uid=system,cn=sysaccounts,cn=etc,dc=bayz,dc=de" method=128 version=3  op=0 RESULT err=0 tag=97 nentries=0 etime=0.0052434415 dn="uid=system,cn=sysaccounts,cn=etc,dc=bayz,dc=de"  op=1 SRCH base="cn=users,cn=accounts,dc=bayz,dc=de" scope=2 filter="(&(objectClass=person)(uid=rwo))" attrs=ALL  op=1 RESULT err=0 tag=101 nentries=1 etime=0.0001797298  op=2 BIND dn="uid=rwo,cn=users,cn=accounts,dc=bayz,dc=de" method=128 version=3  op=2 RESULT err=0 tag=97 nentries=0 etime=0.0052380180 dn="uid=rwo,cn=users,cn=accounts,dc=bayz,dc=de"  op=3 SRCH base="(null)" scope=2 filter="(&(objectClass=person)(uid=rwo))", invalid attribute request  op=3 RESULT err=2 tag=101 nentries=0 etime=0.0000084787  op=-1 fd=112 closed - B1
Since LDAP login still worked fine with other tools I assumed a problem in the new Gitea version and filled a bug report. Other users with the same problem joined soon after, but no one was able to provide a solution.
After some research I figured out that the problem appeared to be related to an update in the FreeIPA server: a security update in the underlying 389 server lead to protocol errors when empty attributes were part of the request.
However, not for me: I still had the problem, and got frustrated over this for weeks.
It took me another evening of research until I found the important missing detail: a Grafana user had the same problem. The updated library did not help there either. But reducing the number of empty attributes by providing values for default, thus otherwise empty attributes did the trick:
For me the error occurs when I have less than 4 attributes.https://github.com/grafana/grafana/issues/14432#issuecomment-452025337
In the end they figured out that one empty attribute was ok to be sent, but not two. With this information, the fix of my problem was easy: I previously had not set the attribute for First Name and Surname. I added those and immediately was able to login again.
So: if you ever run into the same problem with Go and LDAP, check if you are indeed sending more than one empty attribute!
This was the second LDAP problem I encountered using Gitea. Due to this experience I do not really feel comfortable with using this combination – and will not be surprised if it breaks again with the next update.
On the other hand LDAP is a rather complicated protocol and probably a bit overkill for a simple use case like this. If I ever re-do my setup I might change over to mail based authentication.