postfix-sender-login: Better hardening.

Run as a dedicated user, not ‘postfix’.

4 files changed, 59 insertions, 29 deletions

diff --git a/roles/MSA/files/etc/systemd/system/postfix-sender-login.service b/roles/MSA/files/etc/systemd/system/postfix-sender-login.service
index f5e6d89..d652f75 100644
--- a/roles/MSA/files/etc/systemd/system/postfix-sender-login.service
+++ b/roles/MSA/files/etc/systemd/system/postfix-sender-login.service
@@ -4,8 +4,7 @@ After=mail-transport-agent.target
 Requires=postfix-sender-login.socket
 
 [Service]
-User=postfix
-Group=postfix
+User=_postfix-sender-login
 StandardInput=null
 SyslogFacility=mail
 ExecStart=/usr/local/bin/postfix-sender-login.pl
@@ -13,10 +12,9 @@ ExecStart=/usr/local/bin/postfix-sender-login.pl
 # Hardening
 NoNewPrivileges=yes
 PrivateDevices=yes
+PrivateNetwork=yes
 ProtectHome=yes
 ProtectSystem=strict
-PrivateDevices=yes
-PrivateNetwork=yes
 ProtectControlGroups=yes
 ProtectKernelModules=yes
 ProtectKernelTunables=yes
diff --git a/roles/MSA/files/usr/local/bin/postfix-sender-login.pl b/roles/MSA/files/usr/local/bin/postfix-sender-login.pl
index 374cc70..a37f872 100755
--- a/roles/MSA/files/usr/local/bin/postfix-sender-login.pl
+++ b/roles/MSA/files/usr/local/bin/postfix-sender-login.pl
@@ -3,7 +3,7 @@
 #----------------------------------------------------------------------
 # socketmap lookup table returning the SASL login name(s) owning a given
 # sender address
-# Copyright © 2017 Guilhem Moulin <guilhem@fripost.org>
+# Copyright © 2017,2020 Guilhem Moulin <guilhem@fripost.org>
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -33,12 +33,13 @@ use Authen::SASL ();
 $ENV{PATH} = join ':', qw{/usr/bin /bin};
 delete @ENV{qw/IFS CDPATH ENV BASH_ENV/};
 
-my $nProc      = 2;                        # number of pre-forked servers
-my $POSTMASTER = 'postmaster@fripost.org'; # returned for forbidden envelope sender addresses
+my $nProc       = 2;                        # number of pre-forked servers
+my $maxRequests = 32;                       # maximum number of requests per worker
+my $POSTMASTER  = 'postmaster@fripost.org'; # returned for forbidden envelope sender addresses
 
-my $BASEDN  = 'ou=virtual,dc=fripost,dc=org';
+my $BASEDN  = "ou=virtual,dc=fripost,dc=org";
 my $BUFSIZE = 65536; # try to read that many bytes at the time
-my $LDAPI   = 'ldapi://%2Fvar%2Fspool%2Fpostfix-msa%2Fprivate%2Fldapi/';
+my $LDAPI   = "ldapi://";
 sub server();
 
 
@@ -66,7 +67,7 @@ exit $?;
 #############################################################################
 
 sub server() {
-    for (my $n = 0; $n < 32; $n++) {
+    for (my $n = 0; $n < $maxRequests; $n++) {
         accept(my $conn, $S) or do {
             next if $! == EINTR;
             die "accept: $!";
diff --git a/roles/MSA/tasks/main.yml b/roles/MSA/tasks/main.yml
index c78139a..2eee925 100644
--- a/roles/MSA/tasks/main.yml
+++ b/roles/MSA/tasks/main.yml
@@ -6,12 +6,28 @@
     - postfix-pcre
     - postfix-policyd-spf-python
 
+- name: Install Net::LDAP and Authen::SASL
+  apt: pkg={{ packages }}
+  vars:
+    packages:
+    - libnet-ldap-perl
+    - libauthen-sasl-perl
+
 - name: Copy Postfix sender login socketmap
   copy: src=usr/local/bin/postfix-sender-login.pl
         dest=/usr/local/bin/postfix-sender-login.pl
         owner=root group=staff
         mode=0755
 
+- name: Create '_postfix-sender-login' user
+  user: name=_postfix-sender-login system=yes
+        group=nogroup
+        createhome=no
+        home=/nonexistent
+        shell=/usr/sbin/nologin
+        password=!
+        state=present
+
 - name: Copy Postfix sender login socketmap systemd unit files
   copy: src=etc/systemd/system/{{ item }}
         dest=/etc/systemd/system/{{ item }}
diff --git a/roles/common-LDAP/templates/etc/ldap/database.ldif.j2 b/roles/common-LDAP/templates/etc/ldap/database.ldif.j2
index b640cbf..9b4633b 100644
--- a/roles/common-LDAP/templates/etc/ldap/database.ldif.j2
+++ b/roles/common-LDAP/templates/etc/ldap/database.ldif.j2
@@ -267,9 +267,12 @@ olcAccess: to dn.exact="ou=virtual,dc=fripost,dc=org"
     {% if 'MDA' in group_names -%}
     by dn.exact="username=_dovecot-auth-proxy,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://"                                        =sd
     {% endif -%}
-    {% if 'MX' in group_names or 'MSA' in group_names -%}
+    {% if 'MX' in group_names -%}
     by dn.exact="username=postfix,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://%2Fvar%2Fspool%2Fpostfix-[-[:alnum:]]+%2Fprivate%2F" =sd
     {% endif -%}
+    {% if 'MSA' in group_names -%}
+    by dn.exact="username=_postfix-sender-login,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://"                                      =sd
+    {% endif -%}
     {% if 'LDAP_provider' in group_names -%}
     by dn.exact="cn=nextcloud,ou=services,dc=fripost,dc=org"       tls_ssf=128                                                                  =sd
     {% endif -%}
@@ -282,30 +285,35 @@ olcAccess: to dn.exact="ou=virtual,dc=fripost,dc=org"
 #   using a TLS-protected connection.
 # * So has Postfix, when connecting a local ldapi:// socket from the
 #   'private' directory in one of the non-default instance's chroot.
-# * So has _dovecot-auth-proxy on the MDA (for the iterate logic), when
-#   SASL-binding using the EXTERNAL mechanism and connecting to a local
-#   ldapi:// socket.
-# * Amavis may use the entry as searchBase (required to look for the
-#   per-user preferences) but doesn't have read access to the entry.
 # * The 'nobody' UNIX user has read access on the MX:es, when using
 #   SASL-binding using the EXTERNAL mechanism and connecting to a local
 #   ldapi:// socket.  This is required for the 'reserved-alias.pl'
 #   script.
+# * Amavis may use the entry as searchBase (required to look for the
+#   per-user preferences) but doesn't have read access to the entry.
+# * So has _dovecot-auth-proxy on the MDA (for the iterate logic), when
+#   SASL-binding using the EXTERNAL mechanism and connecting to a local
+#   ldapi:// socket.
+# * So has _postfix-sender-login on the submission service to verify
+#   envelope sender ownership
 olcAccess: to dn.regex="^fvd=[^,]+,ou=virtual,dc=fripost,dc=org$"
         attrs=entry,objectClass,fvd
         filter=(&(objectClass=FripostVirtualDomain)(!(objectClass=FripostPendingEntry)))
-    {% if 'LDAP_provider' in group_names -%}
-    {% if groups.MX | difference([inventory_hostname]) -%}
+    {% if 'LDAP_provider' in group_names and groups.MX | difference([inventory_hostname]) -%}
     by dn.exact="cn=mX,ou=syncRepl,dc=fripost,dc=org"              tls_ssf=128                                                                  =rsd
     {% endif -%}
-    {% endif -%}
+    {% if 'MX' in group_names -%}
     by dn.exact="username=postfix,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://%2Fvar%2Fspool%2Fpostfix-[-[:alnum:]]+%2Fprivate%2F" =rsd
+    by dn.exact="username=nobody,cn=peercred,cn=external,cn=auth"  sockurl.regex="^ldapi://"                                                    =rsd
+    {% endif -%}
     {% if 'MDA' in group_names -%}
-    by dn.exact="username=_dovecot-auth-proxy,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://"                                        =rsd
     by dn.exact="username=amavis,cn=peercred,cn=external,cn=auth"  sockurl.regex="^ldapi://"                                                    =sd
     {% endif -%}
-    {% if 'MX' in group_names -%}
-    by dn.exact="username=nobody,cn=peercred,cn=external,cn=auth"  sockurl.regex="^ldapi://"                                                    =rsd
+    {% if 'IMAP' in group_names -%}
+    by dn.exact="username=_dovecot-auth-proxy,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://"                                        =rsd
+    {% endif -%}
+    {% if 'MSA' in group_names -%}
+    by dn.exact="username=_postfix-sender-login,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://"                                      =rsd
     {% endif -%}
     by users                                                                                                                                    =0 break
 #
@@ -383,11 +391,18 @@ olcAccess: to dn.regex="^fvl=[^,]+,fvd=[^,]+,ou=virtual,dc=fripost,dc=org$"
     {% if 'LDAP_provider' in group_names and groups.MX | difference([inventory_hostname]) -%}
     by dn.exact="cn=mX,ou=syncRepl,dc=fripost,dc=org"                      tls_ssf=128                                                                  =rsd
     {% endif -%}
+    {% if 'MX' in group_names -%}
     by dn.exact="username=postfix,cn=peercred,cn=external,cn=auth"         sockurl.regex="^ldapi://%2Fvar%2Fspool%2Fpostfix-[-[:alnum:]]+%2Fprivate%2F" =rsd
+    {% endif -%}
     {% if 'MDA' in group_names -%}
-    by dn.exact="username=_dovecot-auth-proxy,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://"                                                =rsd
     by dn.exact="username=amavis,cn=peercred,cn=external,cn=auth"          sockurl.regex="^ldapi://"                                                    =rsd
     {% endif -%}
+    {% if 'IMAP' in group_names -%}
+    by dn.exact="username=_dovecot-auth-proxy,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://"                                                =rsd
+    {% endif -%}
+    {% if 'MSA' in group_names -%}
+    by dn.exact="username=_postfix-sender-login,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://"                                              =rsd
+    {% endif -%}
     by users                                                                                                                                            =0 break
 #
 # * The SyncRepl MX replicates can check whether a virtual user is
@@ -489,19 +504,19 @@ olcAccess: to dn.regex="^fvl=[^,]+,fvd=[^,]+,ou=virtual,dc=fripost,dc=org$"
     by users                                                                                                                                    =0 break
 {% endif %}
 #
-# * The MSA's postfix user can read entry ownership to dermine the SASL
-#   login name(s) owning a given sender address
+# * The MSA's _postfix-sender-login user can read entry ownership to
+#   dermine the SASL login name(s) owning a given sender address
 {% if 'MSA' in group_names %}
 olcAccess: to dn.regex="^fvd=[^,]+,ou=virtual,dc=fripost,dc=org$"
         attrs=fripostOwner,fripostPostmaster
         filter=(|(objectClass=FripostVirtualAliasDomain)(objectClass=FripostVirtualDomain))
-    by dn.exact="username=postfix,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://%2Fvar%2Fspool%2Fpostfix-[-[:alnum:]]+%2Fprivate%2F" =rsd
-    by users                                                                                                                                    =0 break
+    by dn.exact="username=_postfix-sender-login,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://" =rsd
+    by users                                                                                               =0 break
 olcAccess: to dn.regex="^fvl=[^,]+,fvd=[^,]+,ou=virtual,dc=fripost,dc=org$"
         attrs=entry,objectClass,fvl,fripostOwner
         filter=(|(objectClass=FripostVirtualAlias)(objectClass=FripostVirtualList)(objectClass=FripostVirtualUser))
-    by dn.exact="username=postfix,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://%2Fvar%2Fspool%2Fpostfix-[-[:alnum:]]+%2Fprivate%2F" =rsd
-    by users                                                                                                                                    =0 break
+    by dn.exact="username=_postfix-sender-login,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://" =rsd
+    by users                                                                                               =0 break
 {% endif %}
 {% if 'LDAP_provider' in group_names %}
 #