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
@@ -1,27 +1,25 @@
 [Unit]
 Description=Postfix sender login socketmap
 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
 
 # Hardening
 NoNewPrivileges=yes
 PrivateDevices=yes
+PrivateNetwork=yes
 ProtectHome=yes
 ProtectSystem=strict
-PrivateDevices=yes
-PrivateNetwork=yes
 ProtectControlGroups=yes
 ProtectKernelModules=yes
 ProtectKernelTunables=yes
 RestrictAddressFamilies=AF_UNIX
 
 [Install]
 WantedBy=multi-user.target
 Also=postfix-sender-login.socket
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
@@ -1,89 +1,90 @@
 #!/usr/bin/perl -T
 
 #----------------------------------------------------------------------
 # 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
 # the Free Software Foundation, either version 3 of the License, or
 # (at your option) any later version.
 #
 # This program is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 # GNU General Public License for more details.
 #
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #----------------------------------------------------------------------
 
 use warnings;
 use strict;
 
 use Errno 'EINTR';
 
 use Net::LDAPI ();
 use Net::LDAP::Util qw/ldap_explode_dn escape_dn_value escape_filter_value/;
 use Net::LDAP::Constant qw/LDAP_NO_SUCH_OBJECT/;
 use Authen::SASL ();
 
 # clean up PATH
 $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();
 
 
 # fdopen(3) the file descriptor FD
 die "This service must be socket-activated.\n"
     unless defined $ENV{LISTEN_PID} and $ENV{LISTEN_PID} == $$
        and defined $ENV{LISTEN_FDS} and $ENV{LISTEN_FDS} == 1;
 open my $S, '+<&=', 3 or die "fdopen: $!";
 
 my @CHILDREN;
 for (my $i = 0; $i < $nProc-1; $i++) {
     my $pid = fork() // die "fork: $!";
     if ($pid) {
         push @CHILDREN, $pid;
     } else {
         server(); # child, never return
         exit;
     }
 }
 server();
 waitpid $_ => 0 foreach @CHILDREN;
 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: $!";
         };
         my $reply = process_request($conn);
 
         # encode the reply as a netstring and send it back
         # https://cr.yp.to/proto/netstrings.txt
         $reply = length($reply).':'.$reply.',';
         my $len = length($reply);
 
         for (my $i = 0; $i < $len;) {
             my $n = syswrite($conn, $reply, $len-$i, $i) // do {
                 next if $! == EINTR;
                 warn "Can't write: $!";
                 last;
             };
             $i += $n;
         }
         close $conn or warn "Can't close: $!";
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
@@ -1,34 +1,50 @@
 - name: Install Postfix
   apt: pkg={{ packages }}
   vars:
     packages:
     - postfix
     - 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 }}
         owner=root group=root
         mode=0644
   with_items:
     - postfix-sender-login.service
     - postfix-sender-login.socket
   notify:
     - systemctl daemon-reload
 
 - meta: flush_handlers
 
 - name: Enable Postfix sender login socketmap
   service: name=postfix-sender-login.socket state=started enabled=yes
 
 - name: Configure Postfix
   template: src=etc/postfix/{{ item }}.j2
             dest=/etc/postfix-{{ postfix_instance[inst].name }}/{{ item }}
             owner=root group=root
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
@@ -250,79 +250,87 @@ olcAccess: to dn.subtree="ou=virtual,dc=fripost,dc=org"
     by group.exact="cn=admin,ou=groups,dc=fripost,dc=org"      =wrsd
     by users                                                   =0   break
 olcAccess: to dn.children="ou=virtual,dc=fripost,dc=org"
     by group.exact="cn=admin,ou=groups,dc=fripost,dc=org"      =wrsd
     by users                                                   =0   break
 {% endif -%}
 #
 # * Postfix may use the base as a searchBase on the MX:es, when
 #   connecting a local ldapi:// socket from the 'private' directory in
 #   one of the non-default instance's chroot.
 # * So may _dovecot-auth-proxy on the MDA (needed for the iterate
 #   logic), when SASL-binding using the EXTERNAL mechanism and
 #   connecting to a local ldapi:// socket.
 # * So may Nextcloud on the LDAP provider
 olcAccess: to dn.exact="ou=virtual,dc=fripost,dc=org"
         attrs=entry,objectClass
         filter=(objectClass=FripostVirtual)
     {% 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 -%}
     by users                                                                                                                                    =0 break
 #
 # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
 # Domain entries
 #
 # * The SyncRepl replicates have read access to the entry itself, when
 #   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
 #
 # * The SyncRepl MX replicates can check whether a virtual domain is
 #   active, and read the destination address for catch-alls, when using
 #   a TLS-protected connection.
 # * So can Postfix on the MX:es, when connecting a local ldapi:// socket
 #   from the 'private' directory in one of the non-default instance's
 #   chroot.
 {% if 'MX' in group_names or ('LDAP_provider' in group_names and groups.MX | difference([inventory_hostname])) %}
 olcAccess: to dn.regex="^fvd=[^,]+,ou=virtual,dc=fripost,dc=org$"
         attrs=fripostIsStatusActive,fripostOptionalMaildrop
         filter=(&(objectClass=FripostVirtualDomain)(!(objectClass=FripostPendingEntry)))
     {% 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 -%}
     by users                                                                                                                                    =0 break
@@ -366,45 +374,52 @@ olcAccess: to dn.regex="^fvd=[^,]+,ou=virtual,dc=fripost,dc=org$"
 {% endif %}
 #
 # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
 # User entries
 #
 # * The SyncRepl replicates have read access to the entry itself, when
 #   using a TLS-protected connection.
 # * So has Postfix, when connecting a local ldapi:// socket from the
 #   'private' directory in one of the non-default instance's chroot.
 # * So has _dovecot-auth-proxy on the MDA (for the iterate logic), when
 #   SASL-binding using the EXTERNAL mechanism and connecting to a local
 #   ldapi:// socket.
 # * So has Amavis on the MDA, when SASL-binding using the EXTERNAL
 #   mechanism and connecting to a local ldapi:// socket.
 olcAccess: to dn.regex="^fvl=[^,]+,fvd=[^,]+,ou=virtual,dc=fripost,dc=org$"
         attrs=entry,objectClass,fvl
         filter=(objectClass=FripostVirtualUser)
     {% 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
 #   active, when using a TLS-protected connection.
 # * So can Postfix on the MX:es, when connecting a local ldapi:// socket
 #   from the 'private' directory in one of the non-default instance's
 #   chroot.
 {% if 'MX' in group_names or ('LDAP_provider' in group_names and groups.MX | difference([inventory_hostname])) %}
 olcAccess: to dn.regex="^fvl=[^,]+,fvd=[^,]+,ou=virtual,dc=fripost,dc=org$"
         attrs=fripostIsStatusActive,fripostUseContentFilter
         filter=(objectClass=FripostVirtualUser)
     {% if 'LDAP_provider' in group_names and groups.MX | difference([inventory_hostname]) -%}
     by dn.exact="cn=mX,ou=syncRepl,dc=fripost,dc=org"      tls_ssf=128                                                                          =rsd
     {% endif -%}
     {% if 'MX' in group_names -%}
     by dn.exact="username=postfix,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://%2Fvar%2Fspool%2Fpostfix-[-[:alnum:]]+%2Fprivate%2F" =rsd
     {% endif -%}
     by users                                                                                                                                    =0 break
 {% endif %}
 {% if 'MDA' in group_names %}
@@ -472,53 +487,53 @@ olcAccess: to dn.regex="^fvl=[^,]+,fvd=[^,]+,ou=virtual,dc=fripost,dc=org$"
 {% endif %}
 #
 # * The SyncRepl MX replicates can check whether a virtual list is
 #   active when using a TLS-protected connection.
 # * So can Postfix on the MX:es, when connecting a local ldapi:// socket
 #   from the 'private' directory in one of the non-default instance's
 #   chroot.
 {% if 'MX' in group_names or ('LDAP_provider' in group_names and groups.MX | difference([inventory_hostname])) %}
 olcAccess: to dn.regex="^fvl=[^,]+,fvd=[^,]+,ou=virtual,dc=fripost,dc=org$"
         attrs=fripostIsStatusActive
         filter=(&(objectClass=FripostVirtualList)(!(objectClass=FripostPendingEntry)))
     {% if 'LDAP_provider' in group_names and groups.MX | difference([inventory_hostname]) -%}
     by dn.exact="cn=mX,ou=syncRepl,dc=fripost,dc=org"              tls_ssf=128                                                                  =rsd
     {% endif -%}
     {% if 'MX' in group_names -%}
     by dn.exact="username=postfix,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://%2Fvar%2Fspool%2Fpostfix-[-[:alnum:]]+%2Fprivate%2F" =rsd
     {% endif -%}
     by users                                                                                                                                    =0 break
 {% endif %}
 #
-# * The MSA's postfix user can read entry ownership to dermine the SASL
-#   login name(s) owning a given sender address
+# * The MSA's _postfix-sender-login user can read entry ownership to
+#   dermine the SASL login name(s) owning a given sender address
 {% if 'MSA' in group_names %}
 olcAccess: to dn.regex="^fvd=[^,]+,ou=virtual,dc=fripost,dc=org$"
         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$"
         attrs=entry,objectClass,fvl,fripostOwner
         filter=(|(objectClass=FripostVirtualAlias)(objectClass=FripostVirtualList)(objectClass=FripostVirtualUser))
-    by dn.exact="username=postfix,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://%2Fvar%2Fspool%2Fpostfix-[-[:alnum:]]+%2Fprivate%2F" =rsd
-    by users                                                                                                                                    =0 break
+    by dn.exact="username=_postfix-sender-login,cn=peercred,cn=external,cn=auth" sockurl.regex="^ldapi://" =rsd
+    by users                                                                                               =0 break
 {% endif %}
 {% if 'LDAP_provider' in group_names %}
 #
 # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
 #
 # Export Fripost members to Nextcloud
 olcAccess: to dn.exact="fvd=fripost.org,ou=virtual,dc=fripost,dc=org"
         attrs=entry,objectClass,fvd
         filter=(&(objectClass=FripostVirtualDomain)(!(objectClass=FripostPendingEntry)))
     by dn.exact="cn=nextcloud,ou=services,dc=fripost,dc=org" tls_ssf=128 =rsd
     by users                                                             =0 break
 olcAccess: to dn.regex="^fvl=[^,]+,fvd=fripost.org,ou=virtual,dc=fripost,dc=org$"
         attrs=entry,entryDN,entryUUID,objectClass,fvl,fripostIsStatusActive
         filter=(&(objectClass=FripostVirtualUser)(!(objectClass=FripostPendingEntry))(fripostIsStatusActive=TRUE))
     by dn.exact="cn=nextcloud,ou=services,dc=fripost,dc=org" tls_ssf=128 =rsd
     by users                                                             =0 break
 olcAccess: to dn.exact="ou=groups,dc=fripost,dc=org"
         attrs=entry,objectClass
     by dn.exact="cn=nextcloud,ou=services,dc=fripost,dc=org" tls_ssf=128 =rsd
     by users                                                             =0 break