[Dovecot] Random LDA failure to access auth socket

[Chris Richards]

Greetings all.

Please forgive me if I'm posting something that has already been
addressed, but my google-foo is not strong enough to find the solution.

I've got a dovecot server running version 2.0.19 on Gentoo Hardened.  I
have Postfix as my MTA, and it is calling the Dovecot LDA to deliver the
mail.  Everything is working great, mail is being delivered, and the users
are happy.

However, I am noticing that I have random entries like this:

Mar  1 20:19:23 hermes dovecot: lda: Error: userdb lookup:
connect(/var/run/dovecot/auth-userdb) failed: Permission denied
(euid=97(dovecot) egid=97(dovecot) missing +r perm:
/var/run/dovecot/auth-userdb, dir owned by 0:0 mode=0755)
Mar  1 20:19:23 hermes dovecot: lda: Fatal: Internal error occurred. Refer
to server log for more information.

Since these messages came from the server log, looking in the server log
for more information is rather pointless.

I have 10-master.conf configured as follows:

service auth {
  unix_listener auth-userdb {
    mode = 0600
    user = vmail
    group = vmail
  }

In 15-lda.conf I have:
protocol lda {
  mail_plugins = $mail_plugins sieve quota
}

In Postfix master.cf, I have the following:
dovecot   unix -        n       n       -       -       pipe
  flags=DRhu user=vmail:users argv=/usr/libexec/dovecot/deliver -f
${sender} -d ${user}@${nexthop}

Permissions on the socket are:
srw------- 1 vmail   vmail      0 Feb 24 23:43 auth-userdb

Judging from the log, my problem is that the LDA appears to be trying to
access the socket as the dovecot user (rather than the vmail user), but my
question is why?  What logging can I use to tell me if postfix is calling
with the wrong permissions or if the lda is somehow getting confused?

Any help or suggestions greatly appreciated.

Thanks,
Gizmo