I am trying to authenticate subversion users against sasl+ldap. Other questions about this problem seem to be related to earlier versions of subversion, or sasldb authentication.

lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 8.1 (jessie)
Release:    8.1
Codename:   jessie

svnserve --version
svnserve, version 1.8.10 (r1615264)
Cyrus SASL authentication is available.

saslauthd -v
saslauthd 2.1.26
authentication mechanisms: sasldb getpwent kerberos5 pam rimap shadow ldap

The sasl+LDAP part seems to be correctly configured:

testsaslauthd -u user -p password -r realm
0: OK "Success."

Testing it with wrong credentials gives an error:

testsaslauthd -u wronguser -p wrongpassword -r wrongrealm
0: NO "authentication failed"

And it shows an error in auth.log:

Sep 10 22:23:53 xxx saslauthd[30948]: Entry not found ((&(objectClass=posixAccount)(uid=wronguser))).
Sep 10 22:23:53 xxx saslauthd[30948]: Authentication failed for wronguser/wrongrealm: User not found (-6)
Sep 10 22:23:53 xxx saslauthd[30948]: do_auth         : auth failure: [user=wronguser] [service=imap] [realm=wrongrealm] [mech=ldap] [reason=Unknown]

So I assume SASL can contact the LDAP server fine and get the data.

I configured subversion with:

pwcheck_method: saslauthd
mech_list: DIGEST-MD5

checking svnserve with strace -e open shows that it opens this file, and not /usr/lib/sasl2 or similar.

When I try to connect from a svn client I get

Sep 10 22:31:38 xxx svnserve: DIGEST-MD5 common mech free

in auth.log for each try, but no info or errors from saslauthd.

If I add the user account to sasldb2:

saslpasswd2 user -u realm
Password: password

I can connect from the svn client correctly. So it looks like sasl uses the sasldb2, even though the config for svn and for saslauthd configures LDAP.

  • I have no idea what the answer is, but this is a very nicely crafted question. – womble Sep 10 '15 at 22:09

Solution: I attached a debugger and stepped through the authentication. Turns out I had two problems: Permissions on /var/log/saslauthd:

drwx--x---  2 root        sasl         140 Sep 27 09:44 saslauthd

means the "subversion" server user needs to be part of group sasl.

The second one is more complicated: DIGEST-MD5 relies on plain text passwords to calculate a hash on the server side. My LDAP directory stores SSHA encrypted passwords, so the server could never compare the MD5 from the client with a MD5 computed locally. I guess the directory could store MD5(username:realm:password), but I'm not sure if this is supported in sasl, and how you would manage that if you have several realms.

I don't really want to store plain text passwords, so for now the solution is to only use unencryped authentication:

# cat /etc/sasl2/svn.conf
pwcheck_method: saslauthd
mech_list: PLAIN LOGIN

Not a perfect solution, but it seems to work for now. I think I'll enforce ssh+svn for external access, and maybe I'll invest some time into TLS support for svnserve.

(This would've been much less time consuming with a few more diagnostic options, and better documentation.)

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.