postfix-sender-login: Better hardening.

Run as a dedicated user, not ‘postfix’.

3 files changed, 25 insertions, 10 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 }}