502 lines
18 KiB
Python
502 lines
18 KiB
Python
# PyHeader-Milter is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# PyHeader-Milter is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with PyHeader-Milter. If not, see <http://www.gnu.org/licenses/>.
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#
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__all__ = ["HeaderRule", "HeaderMilter"]
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import Milter
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import argparse
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import configparser
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import logging
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import logging.handlers
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import re
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import sys
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from Milter.utils import parse_addr
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from email.charset import Charset
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from email.header import Header, decode_header
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from netaddr import IPAddress, IPNetwork, AddrFormatError
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def make_header(decoded_seq, maxlinelen=None, header_name=None,
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continuation_ws=' ', errors='strict'):
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"""Create a Header from a sequence of pairs as returned by decode_header()
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decode_header() takes a header value string and returns a sequence of
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pairs of the format (decoded_string, charset) where charset is the string
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name of the character set.
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This function takes one of those sequence of pairs and returns a Header
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instance. Optional maxlinelen, header_name, and continuation_ws are as in
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the Header constructor.
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"""
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h = Header(maxlinelen=maxlinelen, header_name=header_name,
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continuation_ws=continuation_ws)
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for s, charset in decoded_seq:
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# None means us-ascii but we can simply pass it on to h.append()
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if charset is not None and not isinstance(charset, Charset):
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charset = Charset(charset)
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h.append(s, charset, errors=errors)
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return h
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class HeaderRule:
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"""HeaderRule to implement a rule to apply on e-mail headers."""
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def __init__(self, name, action, header, search="", value="",
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ignore_hosts=[], ignore_envfrom=None, only_hosts=[],
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log=True):
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self.logger = logging.getLogger(__name__)
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self.name = name
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self.action = action
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self.header = header
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self.search = search
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self.value = value
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self.ignore_hosts = ignore_hosts
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self.ignore_envfrom = ignore_envfrom
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self.only_hosts = only_hosts
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self.log = log
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if action in ["del", "mod"]:
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# compile header regex
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try:
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self.header = re.compile(
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header, re.MULTILINE + re.DOTALL + re.IGNORECASE)
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except re.error as e:
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raise RuntimeError(
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f"unable to parse option 'header' of rule '{name}': {e}")
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if action == "mod":
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# compile search regex
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try:
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self.search = re.compile(
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search, re.MULTILINE + re.DOTALL + re.IGNORECASE)
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except re.error as e:
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raise RuntimeError(
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f"unable to parse option 'search' of "
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f"rule '{name}': {e}")
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if action in ["add", "mod"] and not value:
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raise RuntimeError("value of option 'value' is empty")
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# replace strings in ignore_hosts and only_hosts with IPNetwork
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# instances
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try:
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for index, ignore in enumerate(ignore_hosts):
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self.ignore_hosts[index] = IPNetwork(ignore)
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except AddrFormatError as e:
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raise RuntimeError(
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f"unable to parse option 'ignore_hosts' of rule '{name}': {e}")
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if self.ignore_envfrom:
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try:
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self.ignore_envfrom = re.compile(ignore_envfrom, re.IGNORECASE)
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except re.error as e:
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raise RuntimeError(
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f"unable to parse option 'ignore_envfrom' of "
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f"rule '{name}': {e}")
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try:
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for index, only in enumerate(only_hosts):
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self.only_hosts[index] = IPNetwork(only)
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except AddrFormatError as e:
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raise RuntimeError(
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f"unable to parse option 'only_hosts' of rule '{name}': {e}")
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def ignore_host(self, host):
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ip = IPAddress(host)
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ignore = False
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# check if host matches ignore_hosts
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for ignored in self.ignore_hosts:
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if ip in ignored:
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ignore = True
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break
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if not ignore and self.only_hosts:
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# host does not match ignore_hosts, check if it matches only_hosts
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ignore = True
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for only in self.only_hosts:
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if ip in only:
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ignore = False
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break
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if ignore:
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self.logger.debug(f"host {host} is ignored by rule {self.name}")
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return ignore
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def ignore_from(self, envfrom):
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ignore = False
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if self.ignore_envfrom:
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if self.ignore_envfrom.search(envfrom):
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ignore = True
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self.logger.debug(
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f"envelope-from {envfrom} is ignored by rule {self.name}")
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return ignore
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def execute(self, headers):
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"""
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Execute rule on given headers and return list
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with modified headers.
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"""
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if self.action == "add":
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return [(self.header, self.value, 0, 1)]
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modified = []
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index = 0
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occurrences = {}
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# iterate headers
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for name, header in headers:
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# keep track of the occurrence of each header, needed by
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# Milter.Base.chgheader
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if name not in occurrences.keys():
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occurrences[name] = 1
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else:
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occurrences[name] += 1
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# check if header line matches regex
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header_line = str(header)
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if self.header.search(header_line):
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value = header_line.split(":", 1)[1].strip()
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if self.action == "del":
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# set an empty value to delete the header
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new_value = ""
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else:
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new_value = self.search.sub(self.value, value)
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if value != new_value:
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header = make_header(
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decode_header(
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f"{name}: {new_value}"), errors="replace")
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modified.append((name, header, index, occurrences[name]))
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index += 1
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return modified
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class HeaderMilter(Milter.Base):
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"""HeaderMilter based on Milter.Base to implement milter communication"""
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_rules = []
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@staticmethod
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def set_rules(rules):
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HeaderMilter._rules = rules
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def __init__(self):
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self.logger = logging.getLogger(__name__)
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# save rules, it must not change during runtime
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self.rules = HeaderMilter._rules.copy()
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def connect(self, IPname, family, hostaddr):
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self.logger.debug(
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f"accepted milter connection from {hostaddr[0]} "
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f"port {hostaddr[1]}")
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ip = IPAddress(hostaddr[0])
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# remove rules which ignore this host
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for rule in self.rules.copy():
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if rule.ignore_host(ip):
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self.rules.remove(rule)
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if not self.rules:
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self.logger.debug(
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f"host {hostaddr[0]} is ignored by all rules, "
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f"skip further processing")
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return Milter.ACCEPT
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return Milter.CONTINUE
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def envfrom(self, mailfrom, *str):
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mailfrom = "@".join(parse_addr(mailfrom)).lower()
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for rule in self.rules.copy():
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if rule.ignore_from(mailfrom):
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self.rules.remove(rule)
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if not self.rules:
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self.logger.debug(
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f"mail from {mailfrom} is ignored by all rules, "
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f"skip further processing")
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return Milter.ACCEPT
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return Milter.CONTINUE
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@Milter.noreply
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def data(self):
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self.qid = self.getsymval('i')
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self.logger.debug(f"{self.qid}: received queue-id from MTA")
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self.headers = []
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return Milter.CONTINUE
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def header(self, name, value):
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try:
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# remove surrogates from value
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value = value.encode(
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errors="surrogateescape").decode(errors="replace")
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self.logger.debug(f"{self.qid}: received header: {name}: {value}")
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header = make_header(
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decode_header(
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f"{name}: {value}"), errors="replace")
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self.logger.debug(
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f"{self.qid}: decoded header: {header}")
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except Exception as e:
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self.logger.exception(
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f"an exception occured in header function: {e}")
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return Milter.TEMPFAIL
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self.headers.append((name, header))
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return Milter.CONTINUE
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def eom(self):
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try:
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for rule in self.rules:
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self.logger.debug(f"{self.qid}: executing rule '{rule.name}'")
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modified = rule.execute(self.headers)
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for name, header, index, occurrence in modified:
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header_line = str(header)
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value = header.encode().split(":", 1)[1].strip()
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if rule.action == "add":
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if rule.log:
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self.logger.info(
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f"{self.qid}: add: header: "
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f"{header_line[0:70]}")
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else:
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self.logger.debug(
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f"{self.qid}: add: header: "
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f"{header_line}")
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self.headers.insert(0, (name, header))
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self.addheader(name, value, 1)
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else:
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if rule.action == "mod":
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old_header = str(self.headers[index][1])
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if rule.log:
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self.logger.info(
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f"{self.qid}: modify: header: "
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f"{old_header[0:70]}: {header_line[0:70]}")
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else:
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self.logger.debug(
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f"{self.qid}: modify: header "
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f"(occ. {occurrence}): {old_header}: "
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f"{header_line}")
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self.headers[index] = (name, header)
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elif rule.action == "del":
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if rule.log:
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self.logger.info(
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f"{self.qid}: delete: header: "
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f"{header_line[0:70]}")
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else:
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self.logger.debug(
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f"{self.qid}: delete: header "
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f"(occ. {occurrence}): {header_line}")
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del self.headers[index]
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self.chgheader(name, occurrence, value)
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return Milter.ACCEPT
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except Exception as e:
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self.logger.exception(
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f"an exception occured in eom function: {e}")
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return Milter.TEMPFAIL
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def main():
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"Run PyHeader-Milter."
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# parse command line
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parser = argparse.ArgumentParser(
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description="PyHeader milter daemon",
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formatter_class=lambda prog: argparse.HelpFormatter(
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prog, max_help_position=45, width=140))
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parser.add_argument(
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"-c", "--config", help="Config file to read.",
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default="/etc/pyheader-milter.conf")
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parser.add_argument(
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"-s",
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"--socket",
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help="Socket used to communicate with the MTA.",
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required=True)
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parser.add_argument(
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"-d",
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"--debug",
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help="Log debugging messages.",
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action="store_true")
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parser.add_argument(
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"-t",
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"--test",
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help="Check configuration.",
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action="store_true")
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args = parser.parse_args()
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# setup logging
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loglevel = logging.INFO
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logname = "pyheader-milter"
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syslog_name = logname
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if args.debug:
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loglevel = logging.DEBUG
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logname = f"{logname}[%(name)s]"
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syslog_name = f"{syslog_name}: [%(name)s] %(levelname)s"
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# set config files for milter class
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root_logger = logging.getLogger()
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root_logger.setLevel(loglevel)
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# setup console log
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stdouthandler = logging.StreamHandler(sys.stdout)
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stdouthandler.setLevel(logging.DEBUG)
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formatter = logging.Formatter("%(message)s")
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stdouthandler.setFormatter(formatter)
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root_logger.addHandler(stdouthandler)
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logger = logging.getLogger(__name__)
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try:
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# read config file
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parser = configparser.ConfigParser()
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if not parser.read(args.config):
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raise RuntimeError("config file not found")
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# check if mandatory config options in global section are present
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if "global" not in parser.sections():
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raise RuntimeError(
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"mandatory section 'global' not present in config file")
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for option in ["rules"]:
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if not parser.has_option("global", option):
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raise RuntimeError(
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f"mandatory option '{option}' not present in config "
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f"section 'global'")
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# read global config section
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global_config = dict(parser.items("global"))
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# read active rules
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active_rules = [r.strip() for r in global_config["rules"].split(",")]
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if len(active_rules) != len(set(active_rules)):
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raise RuntimeError(
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"at least one rule is specified multiple times "
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"in 'rules' option")
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if "global" in active_rules:
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active_rules.remove("global")
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logger.warning(
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"removed illegal rule name 'global' from list of "
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"active rules")
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if not active_rules:
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raise RuntimeError("no rules configured")
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logger.debug("preparing milter configuration ...")
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rules = []
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# iterate active rules
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for rule_name in active_rules:
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# check if config section exists
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if rule_name not in parser.sections():
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raise RuntimeError(
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f"config section '{rule_name}' does not exist")
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config = dict(parser.items(rule_name))
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# check if mandatory option action is present in config
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option = "action"
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if option not in config.keys() and \
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option in global_config.keys():
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config[option] = global_config[option]
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if option not in config.keys():
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raise RuntimeError(
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f"mandatory option '{option}' not specified for "
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f"rule '{rule_name}'")
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config["action"] = config["action"].lower()
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if config["action"] not in ["add", "del", "mod"]:
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raise RuntimeError(
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f"invalid action specified for rule '{rule_name}'")
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# check if mandatory options are present in config
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mandatory = ["header"]
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if config["action"] == "add":
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mandatory += ["value"]
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elif config["action"] == "mod":
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mandatory += ["search", "value"]
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for option in mandatory:
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if option not in config.keys() and \
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option in global_config.keys():
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config[option] = global_config[option]
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if option not in config.keys():
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raise RuntimeError(
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f"mandatory option '{option}' not specified for "
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f"rule '{rule_name}'")
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# check if optional config options are present in config
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defaults = {
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"ignore_hosts": [],
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"ignore_envfrom": None,
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"only_hosts": [],
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"log": "true"
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}
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for option in defaults.keys():
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if option not in config.keys() and \
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option in global_config.keys():
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config[option] = global_config[option]
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if option not in config.keys():
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config[option] = defaults[option]
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if config["ignore_hosts"]:
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config["ignore_hosts"] = [
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h.strip() for h in config["ignore_hosts"].split(",")]
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if config["only_hosts"]:
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config["only_hosts"] = [
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h.strip() for h in config["only_hosts"].split(",")]
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config["log"] = config["log"].lower()
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if config["log"] == "true":
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config["log"] = True
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elif config["log"] == "false":
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config["log"] = False
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else:
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raise RuntimeError(
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f"invalid value specified for option 'log' for "
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f"rule '{rule_name}'")
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# add rule
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logging.debug(f"adding rule '{rule_name}'")
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rules.append(HeaderRule(name=rule_name, **config))
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except RuntimeError as e:
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logger.error(e)
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sys.exit(255)
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if args.test:
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print("Configuration ok")
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sys.exit(0)
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# change log format for runtime
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formatter = logging.Formatter(
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f"%(asctime)s {logname}: [%(levelname)s] %(message)s",
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datefmt="%Y-%m-%d %H:%M:%S")
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stdouthandler.setFormatter(formatter)
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# setup syslog
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sysloghandler = logging.handlers.SysLogHandler(
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address="/dev/log", facility=logging.handlers.SysLogHandler.LOG_MAIL)
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sysloghandler.setLevel(loglevel)
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formatter = logging.Formatter(f"{syslog_name}: %(message)s")
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sysloghandler.setFormatter(formatter)
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root_logger.addHandler(sysloghandler)
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logger.info("PyHeader-Milter starting")
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HeaderMilter.set_rules(rules)
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# register milter factory class
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Milter.factory = HeaderMilter
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Milter.set_exception_policy(Milter.TEMPFAIL)
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rc = 0
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try:
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Milter.runmilter("pyheader-milter", socketname=args.socket, timeout=30)
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except Milter.milter.error as e:
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logger.error(e)
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rc = 255
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logger.info("PyHeader-Milter terminated")
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sys.exit(rc)
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if __name__ == "__main__":
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main()
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