fix: Make Dovecot aware of basic aliases in userdb for quota support + Use correct hash scheme in passdb configuration (#2248)

Dovecot quota support would log auth failures when Postfix validated incoming mail to accept/reject and the `check_policy_service` for `quota-status` was queried with a recipient that was an account alias.

When Dovecot is not aware of the user account, it will not be able to check a quota and inform Postfix that everything is fine, Postfix will accept the mail and send it to Dovecot, where if the quota is exceeded will result in a bounce back to the sender. This is considered "backscatter" and can be abused by spammers forging the sender address which can get your server blacklisted.

The solution is to either disable quota support `ENABLE_QUOTAS=0`, or as a workaround, add dummy accounts to Dovecot userdb for aliases in `postfix-virtual.cf` (not `postfix-aliases.cf`), these dummy accounts will map to the real user account mailbox (real users are defined in `postfix-accounts.cf`).

The workaround is naive, in that we only check for basic 1-to-1 alias mapping to real accounts. This will still be an issue for aliases that map to another alias or multiple addresses (real or alias). Unfortunately Postfix will not expand aliases until accepting mail where this would be too late.

A better solution is to proxy the `check_policy_service` from Dovecot `quota-status` that Postfix queries in `main.cf:smtpd_recipient_restrictions`, however this requires a fair amount more of additional work and still requires an implementation to recursively query aliases for nested or multiple address mappings, which can then be forwarded to the `quota-status` service configured by Dovecot in `/etc/dovecot/conf.d/90-quota.conf`.

LDAP users are unaffected as quota support is not supported/implemented with `docker-mailserver` at this time, it is always considered disabled when using LDAP.

---

Additionally Dovecot configuration for `passdb` has been fixed to use the correct password hash scheme of `SHA512-CRYPT`. 

Co-authored-by: Casper <casperklein@users.noreply.github.com>
Co-authored-by: Brennan Kinney <5098581+polarathene@users.noreply.github.com>

target/dovecot/auth-passwdfile.inc

@@ -1,21 +1,19 @@
 # Authentication for passwd-file users. Included from 10-auth.conf.
 #
-# passwd-like file with specified location.
+# Documentation
-# <doc/wiki/AuthDatabase.PasswdFile.txt>
+#   PassDB: https://doc.dovecot.org/configuration_manual/authentication/password_databases_passdb/
+#   UserDB: https://doc.dovecot.org/configuration_manual/authentication/user_databases_userdb/
+#
+# !!! Attention !!!
+#   Do not add `scheme=SHA512-CRYPT` to the userdb args. This is not supported.
 
 passdb {
   driver = passwd-file
-  args = scheme=CRYPT username_format=%u /etc/dovecot/userdb
+  args = scheme=SHA512-CRYPT username_format=%u /etc/dovecot/userdb
 }
 
 userdb {
   driver = passwd-file
   args = username_format=%u /etc/dovecot/userdb
-
-  # Default fields that can be overridden by passwd-file
-  #default_fields = quota_rule=*:storage=1G
   default_fields = uid=docker gid=docker home=/var/mail/%d/%u
-
-  # Override fields from passwd-file
-  #override_fields = home=/home/virtual/%u
 }

target/scripts/helper-functions.sh

@@ -27,7 +27,7 @@ function dms_panic
 
   local SHUTDOWN_MESSAGE
 
-  case "${PANIC_TYPE}" in
+  case "${PANIC_TYPE:-}" in
     ( 'fail-init' ) # PANIC_INFO == <name of service or process that failed to start / initialize>
       SHUTDOWN_MESSAGE="Failed to start ${PANIC_INFO}!"
       ;;
@@ -53,7 +53,7 @@ function dms_panic
       ;;
   esac
 
-  if [[ -n ${PANIC_SCOPE} ]]
+  if [[ -n ${PANIC_SCOPE:-} ]]
   then
     _shutdown "${PANIC_SCOPE} | ${SHUTDOWN_MESSAGE}"
   else

target/scripts/startup/setup-stack.sh

@@ -332,6 +332,7 @@ function _setup_dovecot_local_user
 
     # creating users ; 'pass' is encrypted
     # comments and empty lines are ignored
+    local LOGIN PASS USER_ATTRIBUTES
     while IFS=$'|' read -r LOGIN PASS USER_ATTRIBUTES
     do
       # Setting variables for better readability
@@ -342,24 +343,31 @@ function _setup_dovecot_local_user
       if [[ -f /tmp/docker-mailserver/dovecot-quotas.cf ]]
       then
         declare -a USER_QUOTA
-        IFS=':' ; read -r -a USER_QUOTA < <(grep "${USER}@${DOMAIN}:" -i /tmp/docker-mailserver/dovecot-quotas.cf)
+        IFS=':' read -r -a USER_QUOTA < <(grep "${USER}@${DOMAIN}:" -i /tmp/docker-mailserver/dovecot-quotas.cf)
-        unset IFS
 
-        [[ ${#USER_QUOTA[@]} -eq 2 ]] && USER_ATTRIBUTES="${USER_ATTRIBUTES} userdb_quota_rule=*:bytes=${USER_QUOTA[1]}"
+        if [[ ${#USER_QUOTA[@]} -eq 2 ]]
+        then
+          USER_ATTRIBUTES="${USER_ATTRIBUTES:+${USER_ATTRIBUTES} }userdb_quota_rule=*:bytes=${USER_QUOTA[1]}"
+        fi
       fi
 
-      # Let's go!
+      if [[ -z ${USER_ATTRIBUTES} ]]
-      _notify 'inf' "user '${USER}' for domain '${DOMAIN}' with password '********', attr=${USER_ATTRIBUTES}"
+      then
+        _notify 'inf' "Creating user '${USER}' for domain '${DOMAIN}'"
+      else
+        _notify 'inf' "Creating user '${USER}' for domain '${DOMAIN}' with attributes '${USER_ATTRIBUTES}'"
+      fi
 
       echo "${LOGIN} ${DOMAIN}/${USER}/" >> /etc/postfix/vmailbox
-      # User database for dovecot has the following format:
+      # Dovecot's userdb has the following format
       # user:password:uid:gid:(gecos):home:(shell):extra_fields
-      # Example :
+      echo \
-      # ${LOGIN}:${PASS}:5000:5000::/var/mail/${DOMAIN}/${USER}::userdb_mail=maildir:/var/mail/${DOMAIN}/${USER}
+        "${LOGIN}:${PASS}:5000:5000::/var/mail/${DOMAIN}/${USER}::${USER_ATTRIBUTES}" \
-      echo "${LOGIN}:${PASS}:5000:5000::/var/mail/${DOMAIN}/${USER}::${USER_ATTRIBUTES}" >> /etc/dovecot/userdb
+        >>/etc/dovecot/userdb
+
       mkdir -p "/var/mail/${DOMAIN}/${USER}"
 
-      # Copy user provided sieve file, if present
+      # copy user provided sieve file, if present
       if [[ -e "/tmp/docker-mailserver/${LOGIN}.dovecot.sieve" ]]
       then
         cp "/tmp/docker-mailserver/${LOGIN}.dovecot.sieve" "/var/mail/${DOMAIN}/${USER}/.dovecot.sieve"
@@ -367,6 +375,65 @@ function _setup_dovecot_local_user
 
       echo "${DOMAIN}" >> /tmp/vhost.tmp
     done < <(grep -v "^\s*$\|^\s*\#" /tmp/docker-mailserver/postfix-accounts.cf)
+
+    # see https://github.com/docker-mailserver/docker-mailserver/pull/2248#issuecomment-953313852
+    # for more details on this section
+    if [[ -f /tmp/docker-mailserver/postfix-virtual.cf ]] && [[ ${ENABLE_QUOTAS} -eq 1 ]]
+    then
+      # adding aliases to Dovecot's userdb
+      # ${REAL_FQUN} is a user's fully-qualified username
+      local ALIAS REAL_FQUN
+      while read -r ALIAS REAL_FQUN
+      do
+        # ignore comments
+        [[ ${ALIAS} == \#* ]] && continue
+
+        # alias is assumed to not be a proper e-mail
+        # these aliases do not need to be added to Dovecot's userdb
+        [[ ! ${ALIAS} == *@* ]] && continue
+
+        # clear possibly already filled arrays
+        # do not remove the following line of code
+        unset REAL_ACC USER_QUOTA
+        declare -a REAL_ACC USER_QUOTA
+
+        local REAL_USERNAME REAL_DOMAINNAME
+        REAL_USERNAME=$(cut -d '@' -f 1 <<< "${REAL_FQUN}")
+        REAL_DOMAINNAME=$(cut -d '@' -f 2 <<< "${REAL_FQUN}")
+
+        if ! grep -q "${REAL_FQUN}" /tmp/docker-mailserver/postfix-accounts.cf
+        then
+          _notify 'inf' "Alias '${ALIAS}' is non-local (or mapped to a non-existing account) and will not be added to Dovecot's userdb"
+          continue
+        fi
+
+        _notify 'inf' "Adding alias '${ALIAS}' for user '${REAL_FQUN}' to Dovecot's userdb"
+
+        # ${REAL_ACC[0]} => real account name (e-mail address) == ${REAL_FQUN}
+        # ${REAL_ACC[1]} => password hash
+        # ${REAL_ACC[2]} => optional user attributes
+        IFS='|' read -r -a REAL_ACC < <(grep "${REAL_FQUN}" /tmp/docker-mailserver/postfix-accounts.cf)
+
+        if [[ -z ${REAL_ACC[1]} ]]
+        then
+          dms_panic__misconfigured 'postfix-accounts.cf' 'alias configuration'
+        fi
+
+        # test if user has a defined quota
+        if [[ -f /tmp/docker-mailserver/dovecot-quotas.cf ]]
+        then
+          IFS=':' read -r -a USER_QUOTA < <(grep "${REAL_FQUN}:" -i /tmp/docker-mailserver/dovecot-quotas.cf)
+          if [[ ${#USER_QUOTA[@]} -eq 2 ]]
+          then
+            REAL_ACC[2]="${REAL_ACC[2]:+${REAL_ACC[2]} }userdb_quota_rule=*:bytes=${USER_QUOTA[1]}"
+          fi
+        fi
+
+        echo \
+          "${ALIAS}:${REAL_ACC[1]}:5000:5000::/var/mail/${REAL_DOMAINNAME}/${REAL_USERNAME}::${REAL_ACC[2]:-}" \
+          >> /etc/dovecot/userdb
+      done < /tmp/docker-mailserver/postfix-virtual.cf
+    fi
   else
     _notify 'inf' "'/tmp/docker-mailserver/postfix-accounts.cf' is not provided. No mail account created."
   fi

test/config/dovecot-lmtp/conf.d/auth-passwdfile.conf.ext

@@ -1,20 +1,19 @@
 # Authentication for passwd-file users. Included from 10-auth.conf.
 #
-# passwd-like file with specified location.
+# Documentation
-# <doc/wiki/AuthDatabase.PasswdFile.txt>
+#   PassDB: https://doc.dovecot.org/configuration_manual/authentication/password_databases_passdb/
+#   UserDB: https://doc.dovecot.org/configuration_manual/authentication/user_databases_userdb/
+#
+# !!! Attention !!!
+#   Do not add `scheme=SHA512-CRYPT` to the userdb args. This is not supported.
 
 passdb {
   driver = passwd-file
-  args = scheme=CRYPT username_format=%u /etc/dovecot/users
+  args = scheme=SHA512-CRYPT username_format=%u /etc/dovecot/userdb
 }
 
 userdb {
   driver = passwd-file
-  args = username_format=%u /etc/dovecot/users
+  args = username_format=%u /etc/dovecot/userdb
-
+  default_fields = uid=docker gid=docker home=/var/mail/%d/%u
-  # Default fields that can be overridden by passwd-file
-  #default_fields = quota_rule=*:storage=1G
-
-  # Override fields from passwd-file
-  #override_fields = home=/home/virtual/%u
 }

test/config/dovecot-lmtp/conf.d/auth-passwdfile.inc

@@ -1,21 +1,19 @@
 # Authentication for passwd-file users. Included from 10-auth.conf.
 #
-# passwd-like file with specified location.
+# Documentation
-# <doc/wiki/AuthDatabase.PasswdFile.txt>
+#   PassDB: https://doc.dovecot.org/configuration_manual/authentication/password_databases_passdb/
+#   UserDB: https://doc.dovecot.org/configuration_manual/authentication/user_databases_userdb/
+#
+# !!! Attention !!!
+#   Do not add `scheme=SHA512-CRYPT` to the userdb args. This is not supported.
 
 passdb {
   driver = passwd-file
-  args = scheme=CRYPT username_format=%u /etc/dovecot/userdb
+  args = scheme=SHA512-CRYPT username_format=%u /etc/dovecot/userdb
 }
 
 userdb {
   driver = passwd-file
   args = username_format=%u /etc/dovecot/userdb
-
-  # Default fields that can be overridden by passwd-file
-  #default_fields = quota_rule=*:storage=1G
   default_fields = uid=docker gid=docker home=/var/mail/%d/%u
-
-  # Override fields from passwd-file
-  #override_fields = home=/home/virtual/%u
 }