414 lines
15 KiB
Python
414 lines
15 KiB
Python
# PyMod-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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# PyMod-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 PyMod-Milter. If not, see <http://www.gnu.org/licenses/>.
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#
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__all__ = [
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"make_header",
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"replace_illegal_chars",
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"run",
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"version",
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"Modification",
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"Rule",
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"ModifyMilter"]
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import Milter
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import logging
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import logging.handlers
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import re
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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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def replace_illegal_chars(string):
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return string.replace(
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"\x00", "").replace(
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"\r", "").replace(
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"\n", "")
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class Modification:
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"""Modification to implement a modification to apply on e-mails."""
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# mandatory parameters for each modification type
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types = {
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"add_header": ["header", "value"],
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"del_header": ["header"],
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"mod_header": ["header", "search", "value"]
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}
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def __init__(self, name, mod_type, log, **params):
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self.logger = logging.getLogger(__name__)
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self.logger.debug(f"initializing modification '{name}'")
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self.name = name
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self.log = log
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# check mod_type
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if mod_type not in Modification.types:
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raise RuntimeError(
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f"{self.name}: invalid modification type '{mod_type}'")
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self.mod_type = mod_type
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# check if mandatory modification options are present in config
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for option in Modification.types[self.mod_type]:
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if option not in params:
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raise RuntimeError(
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f"{self.name}: mandatory config "
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f"option '{option}' not found")
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if option == "value" and not params["value"]:
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raise RuntimeError(
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f"{self.name}: empty value specified")
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if mod_type == "add_header":
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self.header = params["header"]
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self.value = params["value"]
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elif mod_type in ["del_header", "mod_header"]:
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# compile header regex
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try:
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self.header = re.compile(
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params["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"{self.name}: unable to parse regular expression of "
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f"option 'header': {e}")
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if mod_type == "mod_header":
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# compile search regex
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try:
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self.search = re.compile(
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params["search"],
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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"{self.name}: unable to parse regular expression of "
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f"option 'search': {e}")
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self.value = params["value"]
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def execute(self, qid, headers):
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"""
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Execute modification and return list
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with modified headers.
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"""
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if self.mod_type == "add_header":
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header = f"{self.header}: {self.value}"
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if self.log:
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self.logger.info(
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f"{qid}: {self.name}: add_header: {header[0:70]}")
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else:
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self.logger.debug(
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f"{qid}: {self.name}: add_header: {header}")
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return [(self.mod_type, 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, value 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 = f"{name}: {value}"
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if self.header.search(header):
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if self.mod_type == "del_header":
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# set an empty value to delete the header
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new_value = ""
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if self.log:
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self.logger.info(
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f"{qid}: {self.name}: del_header: "
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f"{header[0:70]}")
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else:
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self.logger.debug(
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f"{qid}: {self.name}: del_header: "
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f"(occ. {occurrences[name]}): {header}")
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else:
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old_header = header
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new_value = self.search.sub(self.value, value)
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if value == new_value:
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continue
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header = f"{name}: {new_value}"
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if self.log:
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self.logger.info(
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f"{qid}: {self.name}: mod_header: "
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f"{old_header[0:70]}: {header[0:70]}")
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else:
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self.logger.debug(
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f"{qid}: {self.name}: mod_header: "
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f"(occ. {occurrences[name]}): {old_header}: "
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f"{header}")
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modified.append(
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(self.mod_type, name, new_value, index, occurrences[name]))
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index += 1
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return modified
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class Rule:
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"""
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Rule to implement multiple modifications on emails based on conditions.
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"""
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def __init__(self, name, modifications, local_addrs, log, conditions={}):
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self.logger = logging.getLogger(__name__)
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self.name = name
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self.log = log
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self.logger.debug(f"initializing rule '{self.name}'")
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self._local_addrs = []
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# replace strings in local_addrs list with IPNetwork instances
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try:
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for addr in local_addrs:
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self._local_addrs.append(IPNetwork(addr))
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except AddrFormatError as e:
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raise RuntimeError(
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f"{self.name}: unable to parse entry of "
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f"option local_addrs: {e}")
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self.conditions = {}
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for option, value in conditions.items():
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if option == "local":
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self.conditions[option] = value
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self.logger.debug(
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f"{self.name}: added condition: {option} = {value}")
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elif option == "hosts":
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self.conditions[option] = []
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try:
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for host in value:
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self.conditions[option].append(IPNetwork(host))
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except AddrFormatError as e:
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raise RuntimeError(
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f"{self.name}: unable to parse entry of "
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f"condition '{option}': {e}")
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self.logger.debug(
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f"{self.name}: added condition: {option} = {value}")
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elif option == "envfrom":
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try:
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self.conditions[option] = re.compile(value, re.IGNORECASE)
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except re.error as e:
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raise RuntimeError(
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f"{self.name}: unable to parse regular expression of "
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f"condition '{option}': {e}")
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self.logger.debug(
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f"{self.name}: added condition: {option} = {value}")
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self.modifications = []
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for mod_idx, mod in enumerate(modifications):
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params = {}
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# set default values if not specified in config
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if "name" not in mod:
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mod["name"] = f"Modification #{mod_idx}"
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if self.name:
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params["name"] = f"{self.name}: {mod['name']}"
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else:
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params["name"] = mod["name"]
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if "log" in mod:
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params["log"] = mod["log"]
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else:
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params["log"] = self.log
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if "type" in mod:
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params["mod_type"] = mod["type"]
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else:
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raise RuntimeError(
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f"{params['name']}: mandatory config "
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f"option 'type' not found")
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if "header" in mod:
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params["header"] = mod["header"]
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if "search" in mod:
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params["search"] = mod["search"]
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if "value" in mod:
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params["value"] = mod["value"]
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self.modifications.append(Modification(**params))
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self.logger.debug(
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f"{self.name}: added modification: {mod['name']}")
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def ignore_host(self, host):
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"""Check if host is ignored by this rule."""
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ip = IPAddress(host)
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if "local" in self.conditions:
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is_local = False
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for addr in self._local_addrs:
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if ip in addr:
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is_local = True
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break
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if is_local != self.conditions["local"]:
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return True
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if "hosts" in self.conditions:
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# check if host is in list
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for accepted in self.conditions["hosts"]:
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if ip in accepted:
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return False
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return True
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return False
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def ignore_envfrom(self, envfrom):
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"""Check if envelope-from address is ignored by this rule."""
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if "envfrom" in self.conditions:
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if not self.conditions["envfrom"].search(envfrom):
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return True
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return False
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def execute(self, qid, headers):
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"""Execute all modifications of this rule."""
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changes = []
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if self.log:
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self.logger.info(f"{qid}: executing rule '{self.name}'")
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else:
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self.logger.debug(f"{qid}: executing rule '{self.name}'")
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for mod in self.modifications:
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self.logger.debug(f"{qid}: executing modification '{mod.name}'")
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result = mod.execute(qid, headers)
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changes += result
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for mod_type, name, value, index, occurrence in result:
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if mod_type == "add_header":
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headers.append((name, value))
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else:
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if mod_type == "mod_header":
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headers[index] = (name, value)
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elif mod_type == "del_header":
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del headers[index]
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return changes
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class ModifyMilter(Milter.Base):
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"""ModifyMilter 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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ModifyMilter._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 = ModifyMilter._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.logger.debug(
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f"host {hostaddr[0]} is ignored by rule '{rule.name}'")
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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_envfrom(mailfrom):
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self.logger.debug(
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f"envelope-from {mailfrom} is ignored by "
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f"rule '{rule.name}'")
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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(decode_header(value), errors="replace")
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value = str(header).replace("\x00", "")
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self.logger.debug(
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f"{self.qid}: decoded header: {name}: {value}")
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self.headers.append((name, value))
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return Milter.CONTINUE
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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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def eom(self):
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try:
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for rule in self.rules:
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changes = rule.execute(self.qid, self.headers)
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for mod_type, name, value, index, occurrence in changes:
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enc_value = replace_illegal_chars(
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Header(s=value).encode())
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if mod_type == "add_header":
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self.logger.debug(f"{self.qid}: milter: adding "
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f"header: {name}: {enc_value}")
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self.addheader(name, enc_value, -1)
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else:
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self.logger.debug(f"{self.qid}: milter: modify "
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f"header (occ. {occurrence}): "
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f"{name}: {enc_value}")
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self.chgheader(name, occurrence, enc_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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