4 files changed, 185 insertions, 7 deletions

diff --git a/hosts/surtr/email/ccert-policy-server/ccert_policy_server/__init__.py b/hosts/surtr/email/ccert-policy-server/ccert_policy_server/__init__.py
new file mode 100644
index 00000000..e69de29b
--- /dev/null
+++ b/hosts/surtr/email/ccert-policy-server/ccert_policy_server/__init__.py
diff --git a/hosts/surtr/email/ccert-policy-server/ccert_policy_server/__main__.py b/hosts/surtr/email/ccert-policy-server/ccert_policy_server/__main__.py
new file mode 100644
index 00000000..f481090c
--- /dev/null
+++ b/hosts/surtr/email/ccert-policy-server/ccert_policy_server/__main__.py
@@ -0,0 +1,92 @@
+from systemd.daemon import listen_fds
+from sdnotify import SystemdNotifier
+from socketserver import StreamRequestHandler, ThreadingMixIn
+from systemd_socketserver import SystemdSocketServer
+import sys
+from threading import Thread
+from psycopg_pool import ConnectionPool
+from psycopg.rows import namedtuple_row
+
+import logging
+
+
+class PolicyHandler(StreamRequestHandler):
+    def handle(self):
+        logger.debug('Handling new connection...')
+
+        self.args = dict()
+
+        line = None
+        while line := self.rfile.readline().removesuffix(b'\n'):
+            if b'=' not in line:
+                break
+
+            key, val = line.split(sep=b'=', maxsplit=1)
+            self.args[key.decode()] = val.decode()
+
+        logger.info('Connection parameters: %s', self.args)
+
+        allowed = False
+        with self.server.db_pool.connection() as conn:
+            local, domain = self.args['sender'].split(sep='@', maxsplit=1)
+            extension = None
+            if '+' in local:
+                local, extension = local.split(sep='+', maxsplit=1)
+
+            logger.debug('Parsed address: %s', {'local': local, 'extension': extension, 'domain': domain})
+
+            with conn.cursor() as cur:
+                cur.row_factory = namedtuple_row
+                cur.execute('SELECT "mailbox"."mailbox" as "user", "local", "extension", "domain" FROM "mailbox" INNER JOIN "mailbox_mapping" ON "mailbox".id = "mailbox_mapping"."mailbox" WHERE "mailbox"."mailbox" = %(user)s AND ("local" = %(local)s OR "local" IS NULL) AND ("extension" = %(extension)s OR "extension" IS NULL) AND "domain" = %(domain)s', params = {'user': self.args['ccert_subject'], 'local': local, 'extension': extension if extension is not None else '', 'domain': domain}, prepare=True)
+                for record in cur:
+                    logger.debug('Received result: %s', record)
+                    allowed = True
+
+        action = '550 5.7.0 Sender address not authorized for current user'
+        if allowed:
+            action = 'DUNNO'
+
+        logger.info('Reached verdict: %s', {'allowed': allowed, 'action': action})
+        self.wfile.write(f'action={action}\n\n'.encode())
+
+class ThreadedSystemdSocketServer(ThreadingMixIn, SystemdSocketServer):
+    def __init__(self, fd, RequestHandlerClass):
+        super().__init__(fd, RequestHandlerClass)
+
+        self.db_pool = ConnectionPool(min_size=1)
+        self.db_pool.wait()
+
+def main():
+    global logger
+    logger = logging.getLogger(__name__)
+    console_handler = logging.StreamHandler()
+    console_handler.setFormatter( logging.Formatter('[%(levelname)s](%(name)s): %(message)s') )
+    if sys.stderr.isatty():
+        console_handler.setFormatter( logging.Formatter('%(asctime)s [%(levelname)s](%(name)s): %(message)s') )
+    logger.addHandler(console_handler)
+    logger.setLevel(logging.DEBUG)
+
+    # log uncaught exceptions
+    def log_exceptions(type, value, tb):
+        global logger
+
+        logger.error(value)
+        sys.__excepthook__(type, value, tb) # calls default excepthook
+
+    sys.excepthook = log_exceptions
+
+    fds = listen_fds()
+    servers = [ThreadedSystemdSocketServer(fd, PolicyHandler) for fd in fds]
+
+    if servers:
+        for server in servers:
+            Thread(name=f'Server for fd{server.fileno()}', target=server.serve_forever).start()
+    else:
+        return 2
+
+    SystemdNotifier().notify('READY=1')
+
+    return 0
+
+if __name__ == '__main__':
+    sys.exit(main())
diff --git a/hosts/surtr/email/ccert-policy-server/setup.py b/hosts/surtr/email/ccert-policy-server/setup.py
new file mode 100644
index 00000000..d8eb415a
--- /dev/null
+++ b/hosts/surtr/email/ccert-policy-server/setup.py
@@ -0,0 +1,12 @@
+from setuptools import setup, find_packages
+
+setup(
+    name = 'ccert-policy-server',
+    version = '0.0.0',
+    packages = ['ccert_policy_server'],
+    entry_points = {
+        'console_scripts': [
+            'ccert-policy-server=ccert_policy_server.__main__:main'
+        ],
+    },
+)
diff --git a/hosts/surtr/email/default.nix b/hosts/surtr/email/default.nix
index 83bf02f5..9cfba1f1 100644
--- a/hosts/surtr/email/default.nix
+++ b/hosts/surtr/email/default.nix
@@ -1,4 +1,4 @@
-{ config, pkgs, lib, ... }:
+{ config, pkgs, lib, flakeInputs, ... }:
 
 with lib;
 
@@ -20,6 +20,27 @@ let
     '';
   };
 
+  ccert-policy-server = flakeInputs.mach-nix.lib.${config.nixpkgs.system}.buildPythonPackage {
+    src = ./ccert-policy-server;
+    pname = "ccert-policy-server";
+    version = "0.0.0";
+
+    python = "python39";
+    ignoreDataOutdated = true;
+
+    requirements = ''
+      sdnotify
+      systemd-socketserver
+      psycopg >=3.0.0
+      psycopg-pool >=3.0.0
+      psycopg-binary >=3.0.0
+    '';
+
+    overridesPre = [
+      (self: super: { systemd-python = super.systemd.overrideAttrs (oldAttrs: { pname = "systemd-python"; }); })
+    ];
+  };
+
   spmDomains = ["bouncy.email"];
 in {
   config = {
@@ -35,7 +56,7 @@ in {
         };
       })
     ];
-    
+
     services.postfix = {
       enable = true;
       hostname = "surtr.yggdrasil.li";
@@ -187,8 +208,9 @@ in {
             "-o" "smtpd_tls_ask_ccert=yes"
             "-o" "smtpd_tls_req_ccert=yes"
             "-o" "smtpd_client_restrictions=permit_tls_all_clientcerts,reject"
+            "-o" "{smtpd_data_restrictions = check_policy_service unix:/run/postfwd3/postfwd3.sock}"
             "-o" "smtpd_relay_restrictions=permit_tls_all_clientcerts,reject"
-            "-o" "smtpd_sender_restrictions=reject_unknown_sender_domain,reject_unverified_sender"
+            "-o" "{smtpd_sender_restrictions = reject_unknown_sender_domain,reject_unverified_sender,check_policy_service unix:/run/postfix-ccert-sender-policy.sock}"
             "-o" "unverified_sender_reject_code=550"
             "-o" "unverified_sender_reject_reason={Sender address rejected: undeliverable address}"
             "-o" "smtpd_recipient_restrictions=reject_unauth_pipelining,reject_non_fqdn_recipient,reject_unknown_recipient_domain,permit_tls_all_clientcerts,reject"
@@ -415,7 +437,7 @@ in {
         mail_plugins = $mail_plugins quota
         mailbox_list_index = yes
         postmaster_address = postmaster@yggdrasil.li
-        recipient_delimiter = 
+        recipient_delimiter =
         auth_username_chars = abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890.-+_@
 
         service lmtp {
@@ -431,7 +453,7 @@ in {
         namespace inbox {
           separator = /
           inbox = yes
-          prefix = 
+          prefix =
 
           mailbox Trash {
             auto = no
@@ -602,7 +624,7 @@ in {
           ${pkgs.dovecot_pigeonhole}/bin/sievec $f
         done
       '';
-      
+
       serviceConfig = {
         LoadCredential = [
           "surtr.yggdrasil.li.key.pem:${config.security.acme.certs."surtr.yggdrasil.li".directory}/key.pem"
@@ -703,7 +725,7 @@ in {
     };
     systemd.sockets.spm = {
       wantedBy = [ "nginx.service" ];
-      
+
       socketConfig = {
         ListenStream = "/run/spm/server.sock";
         SocketUser = "spm";
@@ -730,5 +752,57 @@ in {
       enable = true;
       loglevel = "debug";
     };
+
+    systemd.sockets."postfix-ccert-sender-policy" = {
+      requiredBy = ["postfix.service"];
+      wants = ["postfix-ccert-sender-policy.service"];
+      socketConfig = {
+        ListenStream = "/run/postfix-ccert-sender-policy.sock";
+      };
+    };
+    systemd.services."postfix-ccert-sender-policy" = {
+      serviceConfig = {
+        Type = "notify";
+
+        ExecStart = "${ccert-policy-server}/bin/ccert-policy-server";
+
+        Environment = [
+          "PGDATABASE=email"
+        ];
+
+        DynamicUser = false;
+        User = "postfix-ccert-sender-policy";
+        Group = "postfix-ccert-sender-policy";
+        ProtectSystem = "strict";
+        SystemCallFilter = "@system-service";
+        NoNewPrivileges = true;
+        ProtectKernelTunables = true;
+        ProtectKernelModules = true;
+        ProtectKernelLogs = true;
+        ProtectControlGroups = true;
+        MemoryDenyWriteExecute = true;
+        RestrictSUIDSGID = true;
+        KeyringMode = "private";
+        ProtectClock = true;
+        RestrictRealtime = true;
+        PrivateDevices = true;
+        PrivateTmp = true;
+        ProtectHostname = true;
+        ReadWritePaths = ["/run/postgresql"];
+      };
+    };
+    users.users."postfix-ccert-sender-policy" = {
+      isSystemUser = true;
+      group = "postfix-ccert-sender-policy";
+    };
+    users.groups."postfix-ccert-sender-policy" = {};
+
+    services.postfwd = {
+      enable = true;
+      rules = ''
+        id=RCPT01; protocol_state=DATA; protocol_state=END-OF-MESSAGE; action=rcpt(ccert_subject/100/3600/450 4.7.1 Exceeding maximum of 100 recipients per hour [$$ratecount])
+        id=RCPT02; protocol_state=DATA; protocol_state=END-OF-MESSAGE; action=rcpt(ccert_subject/1000/86400/450 4.7.1 Exceeding maximum of 1000 recipients per day [$$ratecount])
+      '';
+    };
   };
 }