Kerberos syncrepl support for OpenLDAP
Jaap Winius
jwinius at umrk.nl
Mon Jan 11 14:33:58 EST 2010
On Sun, 10 Jan 2010 12:58:09 +0000, Jaap Winius wrote:
> ... how to configure things so that syncrepl uses Kerberos
> encryption? I know it's possible, using stuff like GSSAPI
> and kinit cron jobs, ...
Okay, I'll answer this one myself.
Before I begin, let me say that, in this case, Kerberos only offers
encrypted authentication and not data encryption for the OpenLDAP
replication phase; for that it is necessary to set up a Certificate
Authority and use TLS (LDAP over SSL, slapd on port 636).
=== My solution ===
First download k5start (currently found at eyrie.org), compile and
install it on the OpenLDAP consumer server. Then create a simple script
on this host that uses k5start to automatically obtain and periodically
renew a Kerberos TGT for the LDAP service principal (you could use kinit
and a cron job instead, but that solution apparently has certain
weaknesses). Also, the script must run as the user that runs slapd (in my
case the openldap user). The relevant command I used was:
su -c "/usr/local/bin/k5start -U -f /etc/krb5.keytab \
-K 10 -l 24h &" -l openldap
Of course, don't forget to edit /etc/passwd and change the shell setting
for the openldap user to /bin/sh, or else it won't work
Second, I configured syncrepl in slapd.conf to look like this:
syncrepl rid=123
provider=ldap://ldapks.example.com:389/
type=refreshAndPersist
retry="60 30 300 +"
searchbase="dc=example,dc=com"
bindmethod=sasl
saslmech=gssapi
realm=example.com
authcid="ldap/ldapks2.example.com at EXAMPLE.COM"
NB: ldapks2.example.com is the localhost, while ldapks.example.com is an
alias for the OpenLDAP provider server.
Third, it was all was working at this point, except that an an error kept
appearing in the OpenLDAP provider's syslog:
SASL [conn=1] Error: unable to open Berkeley db /etc/sasldb2: \
No such file or directory
There should be a better way to fix this, but I did it by installing a
Debian package, called sasl2-bin. This automatically created the
necessary database file, /etc/sasldb2 database, although I had to be
careful give the openldap user permission to write to it. Slapd never
seems to do that, but at least this prevented it from complaining.
=== Notes ===
Along the way, I did run into two other problems. One was this syslog
error message:
slapd[5395]: SASL [conn=7] Failure: GSSAPI Error: \
Unspecified GSS failure. Minor code may provide \
more information (Key version number for principal \
in key table is incorrect)
This turned out to be due to an invalid Kerberos ticket on the consumer
server.
Another, more inexplicable error that I ran into earlier involved running
an ldapadd that added two entries to the directory on the provider
server: the first addition would succeed (and make it to the consumer),
but the second one would not. The reason was that, at hat point, the
provider slapd had died after writing the first entry to the database. At
the time, the solution appeared to be to install and configure k5start on
the provider the same as on the consumer; it seemed like the provider was
trying to authenticate to the consumer. Unfortunately, I have since not
been able to reproduce this behavior, so I must conclude that problem was
likely unrelated and that a k5start configuration on the provider is not
necessary.
Comments welcome.
Cheers,
Jaap
More information about the Kerberos
mailing list