mirror of
https://github.com/Av0idD4rk/firegex.git
synced 2026-10-23 21:42:05 +00:00
359 lines
13 KiB
Python
359 lines
13 KiB
Python
"""Forgetting UDP flows, so the next datagram of each is steered by the rules in force now.
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Conntrack translates a flow once, at its first packet, and the proxy layer's `redirect`
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is a translation. TCP lives with that: a connection is one thing from its handshake to
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its close, and one opened before the service started is simply carried to the end. UDP
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has no close — a flow lasts for as long as datagrams keep arriving inside the timeout —
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and that turned the same rule into three failures:
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* **a flow older than the service was never filtered**, for as long as it kept talking:
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nothing redirected it, and nothing ever would. A client could open one before the
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protection went up and keep it open indefinitely;
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* **a flow carried across a restart stayed with the engine being retired**, under the
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filters it started with, and kept that engine alive until the drain gave up on it;
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* **and once that engine was gone, the flow went nowhere.** Conntrack went on sending it
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to a relay port nobody listened on, every datagram refreshing the entry that did so,
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until the client happened to fall silent for two minutes.
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A UDP flow can simply be forgotten: its next datagram is a new flow, judged by whatever
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rules are there now, and neither end had any state that depended on the old entry. So
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this deletes the entries, over ctnetlink — the kernel's own interface, the one the
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`conntrack` tool speaks, with nothing to install and nothing to spawn.
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TCP is never touched here: forgetting a connection breaks it.
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"""
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import ipaddress
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import socket
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import struct
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from dataclasses import dataclass
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from typing import Callable, Iterable
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NETLINK_NETFILTER = 12
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NLM_F_REQUEST = 0x1
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NLM_F_ACK = 0x4
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NLM_F_DUMP = 0x300
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NLMSG_ERROR = 2
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NLMSG_DONE = 3
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NFNL_SUBSYS_CTNETLINK = 1
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IPCTNL_MSG_CT_GET = 1
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IPCTNL_MSG_CT_DELETE = 2
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NLA_TYPE_MASK = 0x3FFF
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CTA_TUPLE_ORIG = 1
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CTA_TUPLE_REPLY = 2
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CTA_STATUS = 3
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CTA_MARK = 8
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CTA_ZONE = 18
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CTA_TUPLE_IP = 1
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CTA_TUPLE_PROTO = 2
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CTA_IP_V4_SRC = 1
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CTA_IP_V4_DST = 2
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CTA_IP_V6_SRC = 3
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CTA_IP_V6_DST = 4
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CTA_PROTO_NUM = 1
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CTA_PROTO_SRC_PORT = 2
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CTA_PROTO_DST_PORT = 3
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#: `IPS_DST_NAT`: the flow's destination was rewritten — by a `redirect`, among others.
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IPS_DST_NAT = 1 << 5
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IPPROTO_UDP = 17
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_HEADER = struct.Struct("=IHHII")
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_NFGEN = struct.Struct("=BBH")
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_ATTR = struct.Struct("=HH")
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@dataclass
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class Flow:
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"""One conntrack entry, as much of it as deciding and deleting need."""
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family: int
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l4proto: int
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orig_src: ipaddress._BaseAddress | None
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orig_dst: ipaddress._BaseAddress | None
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orig_sport: int | None
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orig_dport: int | None
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reply_src: ipaddress._BaseAddress | None
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reply_sport: int | None
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status: int
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mark: int
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#: The original tuple and the zone exactly as the kernel sent them, which is what a
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#: delete names the entry by.
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raw_orig: bytes
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raw_zone: bytes = b""
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@property
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def redirected(self) -> bool:
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return bool(self.status & IPS_DST_NAT)
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# --- the wire -------------------------------------------------------------------
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def _align(n: int) -> int:
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return (n + 3) & ~3
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def attr(kind: int, payload: bytes) -> bytes:
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"""One netlink attribute, padded."""
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raw = _ATTR.pack(_ATTR.size + len(payload), kind) + payload
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return raw + b"\0" * (_align(len(raw)) - len(raw))
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def attrs(data: bytes) -> Iterable[tuple[int, bytes, bytes]]:
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"""`(type, payload, the whole attribute)` for each attribute in `data`."""
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pos = 0
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while pos + _ATTR.size <= len(data):
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length, kind = _ATTR.unpack_from(data, pos)
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if length < _ATTR.size or pos + length > len(data):
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return
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yield kind & NLA_TYPE_MASK, data[pos + _ATTR.size:pos + length], data[pos:pos + length]
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pos += _align(length)
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def message(kind: int, flags: int, seq: int, family: int, payload: bytes = b"") -> bytes:
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body = _NFGEN.pack(family, 0, 0) + payload
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return _HEADER.pack(_HEADER.size + len(body), (NFNL_SUBSYS_CTNETLINK << 8) | kind,
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flags, seq, 0) + body
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def messages(data: bytes) -> Iterable[tuple[int, bytes]]:
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"""`(type, payload)` for each netlink message in one read."""
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pos = 0
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while pos + _HEADER.size <= len(data):
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length, kind, _flags, _seq, _pid = _HEADER.unpack_from(data, pos)
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if length < _HEADER.size or pos + length > len(data):
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return
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yield kind, data[pos + _HEADER.size:pos + length]
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pos += _align(length)
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def _tuple(data: bytes) -> tuple:
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src = dst = sport = dport = None
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proto = 0
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for kind, payload, _ in attrs(data):
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if kind == CTA_TUPLE_IP:
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for ip_kind, value, _ in attrs(payload):
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if ip_kind in (CTA_IP_V4_SRC, CTA_IP_V6_SRC):
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src = ipaddress.ip_address(value)
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elif ip_kind in (CTA_IP_V4_DST, CTA_IP_V6_DST):
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dst = ipaddress.ip_address(value)
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elif kind == CTA_TUPLE_PROTO:
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for proto_kind, value, _ in attrs(payload):
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if proto_kind == CTA_PROTO_NUM:
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proto = value[0]
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elif proto_kind == CTA_PROTO_SRC_PORT:
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sport = struct.unpack("!H", value[:2])[0]
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elif proto_kind == CTA_PROTO_DST_PORT:
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dport = struct.unpack("!H", value[:2])[0]
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return src, dst, sport, dport, proto
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def parse_flow(payload: bytes) -> Flow | None:
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"""A conntrack entry out of one `IPCTNL_MSG_CT_NEW` message's payload."""
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if len(payload) < _NFGEN.size:
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return None
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family = payload[0]
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orig = reply = None
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raw_orig = raw_zone = b""
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status = mark = 0
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for kind, value, whole in attrs(payload[_NFGEN.size:]):
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if kind == CTA_TUPLE_ORIG:
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orig, raw_orig = _tuple(value), whole
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elif kind == CTA_TUPLE_REPLY:
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reply = _tuple(value)
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elif kind == CTA_STATUS:
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status = struct.unpack("!I", value[:4])[0]
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elif kind == CTA_MARK:
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mark = struct.unpack("!I", value[:4])[0]
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elif kind == CTA_ZONE:
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raw_zone = whole
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if orig is None:
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return None
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reply_src, _, reply_sport, _, _ = reply if reply else (None, None, None, None, 0)
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return Flow(
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family=family, l4proto=orig[4],
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orig_src=orig[0], orig_dst=orig[1], orig_sport=orig[2], orig_dport=orig[3],
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reply_src=reply_src, reply_sport=reply_sport,
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status=status, mark=mark, raw_orig=raw_orig, raw_zone=raw_zone,
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)
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def delete_request(flow: Flow, seq: int) -> bytes:
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return message(IPCTNL_MSG_CT_DELETE, NLM_F_REQUEST | NLM_F_ACK, seq, flow.family,
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flow.raw_orig + flow.raw_zone)
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# --- talking to the kernel ------------------------------------------------------
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def _read_until_done(sock: socket.socket) -> Iterable[bytes]:
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"""The payload of every entry a dump answers with."""
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while True:
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data = sock.recv(1 << 18)
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if not data:
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return
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for kind, payload in messages(data):
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if kind == NLMSG_DONE:
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return
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if kind == NLMSG_ERROR:
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error = struct.unpack_from("=i", payload)[0] if len(payload) >= 4 else 0
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if error:
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raise OSError(-error, "conntrack dump refused")
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return
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yield payload
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def _acknowledged(sock: socket.socket) -> int:
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"""The error a request was answered with, 0 for none."""
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while True:
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for kind, payload in messages(sock.recv(1 << 16)):
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if kind == NLMSG_ERROR:
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return -struct.unpack_from("=i", payload)[0] if len(payload) >= 4 else 0
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def delete_where(chosen: Callable[[Flow], bool]) -> int:
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"""Delete every UDP entry `chosen` picks. Returns how many went.
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The table is read once and the deletes follow: a flow that ended in between is
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answered `ENOENT`, which is the state being asked for.
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"""
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with socket.socket(socket.AF_NETLINK, socket.SOCK_RAW, NETLINK_NETFILTER) as sock:
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sock.settimeout(5)
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sock.bind((0, 0))
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sock.send(message(IPCTNL_MSG_CT_GET, NLM_F_REQUEST | NLM_F_DUMP, 1, socket.AF_UNSPEC))
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doomed = []
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for payload in _read_until_done(sock):
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flow = parse_flow(payload)
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if flow is not None and flow.l4proto == IPPROTO_UDP and chosen(flow):
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doomed.append(flow)
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gone = 0
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for seq, flow in enumerate(doomed, start=2):
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sock.send(delete_request(flow, seq))
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error = _acknowledged(sock)
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if error == 0:
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gone += 1
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elif error != 2: # ENOENT: it ended by itself meanwhile
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raise OSError(error, "conntrack refused a delete")
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return gone
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# --- what to forget -------------------------------------------------------------
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Target = tuple[ipaddress.IPv4Network | ipaddress.IPv6Network, int]
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def targets(pairs: Iterable[tuple[str, int]]) -> list[Target]:
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"""`(address or network, port)` pairs as something a flow can be compared with."""
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return [(ipaddress.ip_network(str(ip), strict=False), int(port)) for ip, port in pairs]
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def headed_for(flow: Flow, wanted: list[Target]) -> bool:
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"""Whether a flow was going to one of `wanted` before anything rewrote it."""
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if flow.orig_dst is None or flow.orig_dport is None:
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return False
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return any(
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flow.orig_dport == port and flow.orig_dst.version == network.version
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and flow.orig_dst in network
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for network, port in wanted
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)
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def chooser(*, moved: list[Target], unsteered: list[Target], spare_mark: int,
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bound: set[int]) -> Callable[[Flow], bool]:
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"""Which flows `forget_udp` lets go of. Split out so the decision can be tested
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without a kernel."""
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def chosen(flow: Flow) -> bool:
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if flow.mark == spare_mark:
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return False
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if headed_for(flow, moved):
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return True
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if headed_for(flow, unsteered):
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return not flow.redirected or flow.reply_sport not in bound
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return False
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return chosen
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def forget_udp(*, moved: Iterable[tuple[str, int]] = (),
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unsteered: Iterable[tuple[str, int]] = (), spare_mark: int) -> int:
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"""Forget UDP flows headed for these addresses, so their next datagram is steered by
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the rules in force now.
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* `moved`: every flow headed there, including the ones a redirect already took to an
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engine — a datagram flow can change engines between two datagrams and lose nothing
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but the filter's own state for it, which is what a new configuration costs anyway.
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* `unsteered`: only the ones nothing is carrying — never redirected at all, or
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redirected to a port nobody listens on any more. What a QUIC edge needs: its
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connections are terminated by an engine, and moved to another one mid-connection
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they would end, while one still draining is carrying them.
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`spare_mark` is the engine's own: its dials to the service are flows headed for the
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same address, and they are its to keep.
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"""
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moved_to, unsteered_to = targets(moved), targets(unsteered)
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if not moved_to and not unsteered_to:
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return 0
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return delete_where(chooser(
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moved=moved_to, unsteered=unsteered_to, spare_mark=spare_mark,
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bound=bound_udp_ports() if unsteered_to else set(),
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))
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def bound_udp_ports() -> set[int]:
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"""Every UDP port some socket on this host is bound to, from `/proc/net/udp{,6}`."""
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found = set()
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for path in ("/proc/net/udp", "/proc/net/udp6"):
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try:
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with open(path) as table:
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next(table, None)
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for line in table:
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fields = line.split()
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if len(fields) > 1 and ":" in fields[1]:
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found.add(int(fields[1].rsplit(":", 1)[1], 16))
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except OSError:
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continue
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return found
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def forget_udp_redirected_to(ports: Iterable[int], local: set) -> int:
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"""Forget the UDP flows a redirect sent to one of these ports on this host.
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What is left of an engine once it has gone: every such flow points at a relay nobody
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listens on any more. Recognised by the reply coming from that port on one of this
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host's own addresses — which is what a redirect writes into the reply tuple, and what
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no flow forwarded to a container or another host can have.
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"""
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wanted = {int(port) for port in ports}
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if not wanted:
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return 0
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return delete_where(
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lambda flow: flow.redirected and flow.reply_sport in wanted
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and flow.reply_src is not None and flow.reply_src in local
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)
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def local_addresses() -> set:
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"""Every address this host holds right now."""
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import psutil
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found = set()
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for entries in psutil.net_if_addrs().values():
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for entry in entries:
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if entry.family in (socket.AF_INET, socket.AF_INET6):
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try:
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found.add(ipaddress.ip_address(entry.address.split("%")[0]))
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except ValueError:
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pass
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return found
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