[Dovecot] system account delivery userdb authentication
Hi
I have a remaining issue with a mail server setup.
Composed of Postfix and Dovecot it is is a 'local' mail server At first I relied upon Mysql to store the various parameters, and then switched to a flat file approach
I also initially set the server up to handle virtual users, but then I realized that it was destined to manage local system accounts only. So I reconfigured it accordingly
Relying on system accounts for authentication means that the domain name component is absent from the username (as opposed to virtual user identifiers)
This caused me some difficulty at first with roundcube, but I was able to get around it through a manual adjustment in Mysql
The remaining aspect that isn't working is the delivery of emails.
The entry in master.cf for dovecot looks looks this:
dovecot unix - n n - - pipe flags=DRhu user=mail:mail argv=/usr/lib/dovecot/deli ver -d ${recipient}
The problem is that the recipient equates to the users email address, which can't in fact be used for authentication purposes with system accounts.
I then tried replacing recipient with user:
dovecot unix - n n - - pipe flags=DRhu user=mail:mail argv=/usr/lib/dovecot/deliver -d ${user}
There seems to be a rights issue because I get the following error:
dovecot Fatal: setgid(100(users)) failed with euid=8(mail), gid=8(mail), egid=8(mail): Operation not permitted
Any ideas ?
thanks
yann
# 1.2.15: /etc/dovecot/dovecot.conf # OS: Linux 2.6.32-5-686 i686 Debian 6.0.7 ext4 log_timestamp: %d-%m-%Y %H:%M:%S protocols: imap imaps pop3 pop3s ssl_cert_file: /etc/ssl/certs/postfix.pem ssl_key_file: /etc/ssl/private/postfix.key login_dir: /var/run/dovecot/login login_executable(default): /usr/lib/dovecot/imap-login login_executable(imap): /usr/lib/dovecot/imap-login login_executable(pop3): /usr/lib/dovecot/pop3-login mail_privileged_group: mail mail_location: maildir:/var/mail/%u mbox_write_locks: fcntl dotlock mail_executable(default): /usr/lib/dovecot/imap mail_executable(imap): /usr/lib/dovecot/imap mail_executable(pop3): /usr/lib/dovecot/pop3 mail_plugin_dir(default): /usr/lib/dovecot/modules/imap mail_plugin_dir(imap): /usr/lib/dovecot/modules/imap mail_plugin_dir(pop3): /usr/lib/dovecot/modules/pop3 lda: auth_socket_path: /var/run/dovecot/auth-master postmaster_address: postmaster@holinice.com mail_plugins: sieve log_path: syslog_facility: mail auth default: mechanisms: plain login verbose: yes passdb: driver: pam userdb: driver: passwd socket: type: listen client: path: /var/spool/postfix/private/auth mode: 432 user: postfix group: postfix master: path: /var/run/dovecot/auth-master mode: 432 user: mail group: mail
At 10PM +0200 on 28/05/13 you (Yann Shukor) wrote:
The remaining aspect that isn't working is the delivery of emails.
The entry in master.cf for dovecot looks looks this:
dovecot unix - n n - - pipe flags=DRhu user=mail:mail argv=/usr/lib/dovecot/deli ver -d ${recipient}
[Just like someone who was posting a little while ago, your Dovecot binaries are under /usr/lib. This is very weird: they should really be under /usr/libexec...]
The problem is that the recipient equates to the users email address, which can't in fact be used for authentication purposes with system accounts.
You can get around this problem with auth_username_format on the Dovecot side. On my system I have
auth_username_format = %Luwhich instructs Dovecot to look up users by the lowercased username part only. It's also best, when passing a recipient address to the LDA, to use -a rather than -d, since this will also strip off any +extension to the username (assuming you've configured Postfix and Dovecot to use the same extension character), while making it available to Sieve scripts later on.
I then tried replacing recipient with user:
dovecot unix - n n - - pipe flags=DRhu user=mail:mail argv=/usr/lib/dovecot/deliver -d ${user}
There seems to be a rights issue because I get the following error:
dovecot Fatal: setgid(100(users)) failed with euid=8(mail), gid=8(mail), egid=8(mail): Operation not permitted
Think a bit about what's going on here. Postfix is running deliver as user 'mail', and you're passing the -d argument, so deliver looks up that user in the userdb and tries to setuid and setgid to the uid and gid for that user. Since 'mail' is neither the target u/gid nor root, it is not allowed to do that.
There are three basic strategies here. The first, and in some ways the simplest, is to forget you're using 'system users' and store all the mails under the 'mail' userid. This means you need to configure Dovecot just as you had for virtual users: in particular, the Dovecot userdb should return mail's u/gid for all users, and each user needs a 'Dovecot home directory' owned by 'mail'. (You can easily do this with the 'static' userdb, just as you would have for virtual users.)
The advantage here is the simplicity. The disadvantages are: first, that users logged in to the mail server can't access their own mail spool directly but have to go through IMAP (probably not important, but this was the historical reason for doing deliveries as the delivered-to user); second, that if you have any OS-level filesystem quotas set up a user's mail will be counted against mail's quota rather than their own; and third, that there is a small chance a user might find some way to break Dovecot's 'imap' process and use it to read or modify other people's mail.
The second, which is what I currently do, is to use Postfix's local(8) delivery agent, which runs as root and setuids down to the delivered-to user's uid before doing final delivery. You can get local(8) to deliver through Dovecot by setting Postfix's mailbox_command parameter: the important thing here is that when the LDA is invoked it already has the correct u/gid. With this method you keep the other features of local(8), like /etc/aliases and .forward files; this may be an advantage or a disadvantage depending on your setup.
The third is to have the Dovcot delivery process running as root, so it can successfully setuid down to the user's credentials itself. Probably the easiest way to do this is to use the LMTP server (and Postfix's lmtp(8) transport rather than a dedicated Dovecot master.cf entry), though I would expect that if you simply changed that LDA entry to 'user=root:wheel' that the LDA would correctly setuid down to the user's credentials before doing any deliveries. This is what I would recommend for a new installation; the only reason I don't do this is because I upgraded from 1.2, which didn't have LMTP, and I haven't got round to migrating yet.
# 1.2.15: /etc/dovecot/dovecot.conf
Oh Lord, you're still using 1.2... Don't do that. Use the latest 2.1. You can get Debian packages from http://wiki2.dovecot.org/PrebuiltBinaries .
Ben
participants (2)
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Ben Morrow
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Yann Shukor