I’m trying to configure dovecot lmtp in multi-user mode. My error logs are filled with messages saying that an imap process cannot do a setuid to another user:

May 21 22:28:46 imap(pid 17441 user myuser): Fatal: setuid(512(myuser) from userdb lookup) failed with euid=501(adminuser): Operation not permitted (This binary should probably be called with process user set to 512(myuser) instead of 501(adminuser))

I see that others have had similar issues, but I am not able to apply any of the fixes or workarounds to solve this issue (e.g. setting libexec/dovecot/imap as setuid-root). I’ve also tried other fixes like setting the permissions to 0777 on the userdb auth for postfix smtpd.

According to the code (restrict-access.c, linked below), it appears that when a user authenticates, an imap worker process is launched that has the bid of the authenticator. When another user authenticates, this last process is used, but it does not have the permissions to perform a setuid to the new user, resulting in the Fatal error that appears in the logs.

Is this a bug, or a configuration issue? I’ve posted my doveconf below.

Any pointers would be greatly appreciated.

Steve

Related: https://serverfault.com/questions/930245/dovecot-operation-not-permitted <https://serverfault.com/questions/930245/dovecot-operation-not-permitted> https://dovecot.org/list/dovecot/2012-May/135549.html <https://dovecot.org/list/dovecot/2012-May/135549.html> https://trac.macports.org/ticket/58506 <https://trac.macports.org/ticket/58506>

Code at https://github.com/dovecot/core/blob/master/src/lib/restrict-access.c <https://github.com/dovecot/core/blob/master/src/lib/restrict-access.c>: https://github.com/dovecot/core/blob/863887d4272f962926ab279ac4cf37855dd2008... <https://github.com/dovecot/core/blob/863887d4272f962926ab279ac4cf37855dd2008d/src/lib/restrict-access.c#L238-L256> https://github.com/dovecot/core/blob/863887d4272f962926ab279ac4cf37855dd2008... <https://github.com/dovecot/core/blob/863887d4272f962926ab279ac4cf37855dd2008d/src/lib/restrict-access.c#L342-L346>

doveconf -n:

# 2.3.0.1 (ffd8a29): /opt/local/etc/dovecot/dovecot.conf # Pigeonhole version 0.5.0.1 (d33dca20) # OS: Darwin 18.6.0 x86_64 apfs auth_cache_size = 10 M auth_gssapi_hostname = $ALL auth_krb5_keytab = /opt/local/etc/dovecot/imap.keytab auth_mechanisms = plain gssapi auth_realms = host.domain.tld auth_socket_path = /opt/local/var/run/dovecot/auth-userdb auth_username_format = %Ln debug_log_path = /opt/local/var/log/mail/mail-debug.log default_internal_user = _dovecot default_login_user = _dovenull disable_plaintext_auth = no first_valid_gid = 6 first_valid_uid = 6 imap_id_log = * imap_id_send = "name" * "version" * imap_idle_notify_interval = 29 mins imap_urlauth_submit_user = submit info_log_path = /opt/local/var/log/mail/mail-info.log last_valid_gid = 100 lda_mailbox_autocreate = yes log_path = /opt/local/var/log/mail/mail-err.log login_log_format_elements = user=<%u> method=%m rip=%r lip=%l mpid=%e %c mail_access_groups = mail mail_attachment_dir = /private/var/mail/tld.domain.mail/attachments mail_attachment_fs = sis posix:mode=0666 mail_debug = yes mail_gid = mail mail_home = /private/var/mail/tld.domain.mail mail_location = mdbox:/private/var/mail/tld.domain.mail/%Ln/mdbox mail_log_prefix = "%s(pid %p user %u): " mail_plugins = quota zlib acl fts fts_solr fts_lucene mail_privileged_group = mail mail_uid = _dovecot managesieve_notify_capability = mailto managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date index ihave duplicate mime foreverypart extracttext imapsieve vnd.dovecot.imapsieve mdbox_rotate_size = 200 M namespace inbox { inbox = yes location = mailbox Archive { auto = subscribe special_use = \Archive } mailbox Drafts { auto = subscribe special_use = \Drafts } mailbox Junk { auto = create special_use = \Junk } mailbox Notspam_train { auto = create special_use = \Junk } mailbox Sent { auto = subscribe special_use = \Sent } mailbox Spam_train { auto = create special_use = \Junk } mailbox Trash { auto = create special_use = \Trash } prefix = separator = / } passdb { driver = pam name = pam } plugin { fts = solr fts_autoindex = yes fts_autoindex_exclude = \Junk fts_solr = url=http://127.0.0.1:8983/solr/dovecot/ imapsieve_mailbox1_before = file:/opt/local/etc/dovecot/sieve/report-spam.sieve imapsieve_mailbox1_causes = COPY APPEND imapsieve_mailbox1_name = Spam_train imapsieve_mailbox2_before = file:/opt/local/etc/dovecot/sieve/report-ham.sieve imapsieve_mailbox2_causes = COPY APPEND imapsieve_mailbox2_name = Notspam_train mail_log_events = delete undelete expunge copy mailbox_delete mailbox_rename mail_log_fields = uid box msgid from subject size flags quota_grace = 10%% quota_rule = *:storage=16G quota_rule2 = Trash:storage=+256M quota_warning = storage=100%% quota-exceeded %u quota_warning2 = storage=80%% quota-warning %u recipient_delimiter = + sieve = /private/var/mail/tld.domain.mail/rules/%Ln/dovecot.sieve sieve_after = /opt/local/etc/dovecot/sieve-after.d sieve_before = /opt/local/etc/dovecot/sieve-before.d sieve_dir = /private/var/mail/tld.domain.mail/rules/%Ln/%u sieve_global_extensions = +vnd.dovecot.pipe +vnd.dovecot.environment sieve_pipe_bin_dir = /opt/local/etc/dovecot/sieve sieve_plugins = sieve_imapsieve sieve_extprograms sieve_quota_max_storage = 50M } postmaster_address = postmaster@domain.tld protocols = imap lmtp sieve quota_full_tempfail = yes sendmail_path = /opt/local/sbin/sendmail service auth-worker { user = root } service auth { extra_groups = _keytabusers idle_kill = 15 mins unix_listener /opt/local/var/spool/postfix/private/auth { group = mail mode = 0660 user = _postfix } } service imap-login { inet_listener imap { address = 127.0.0.1, ::1 port = 143 } inet_listener imaps { port = 993 ssl = yes } process_min_avail = 6 service_count = 0 vsz_limit = 2 G } service imap { client_limit = 16 process_limit = 200 process_min_avail = 6 service_count = 0 } service lmtp { unix_listener /opt/local/var/spool/postfix/private/dovecot-lmtp { group = mail mode = 0660 user = _postfix } } ssl = required ssl_ca = </etc/certificates/chain.pem ssl_cert = </etc/certificates/cert.pem ssl_cipher_list = ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256 ssl_dh = # hidden, use -P to show it ssl_key = # hidden, use -P to show it ssl_min_protocol = TLSv1.2 ssl_prefer_server_ciphers = yes userdb { driver = passwd name = passwd } verbose_proctitle = yes protocol lda { mail_fsync = optimized mail_plugins = quota zlib acl fts fts_solr fts_lucene sieve } protocol imap { mail_max_userip_connections = 50 mail_plugins = quota zlib acl fts fts_solr fts_lucene imap_acl imap_quota imap_zlib imap_sieve } protocol lmtp { mail_fsync = optimized mail_plugins = quota zlib acl fts fts_solr fts_lucene sieve }