269 lines
9.4 KiB
Python
269 lines
9.4 KiB
Python
import math
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import os
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import pytest
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import socket
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import subprocess
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import sys
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import trio
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import unshare
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import netfilterqueue
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from typing import AsyncIterator
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from async_generator import asynccontextmanager
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from pytest_trio.enable_trio_mode import *
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# We'll create three network namespaces, representing a router (which
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# has interfaces on ROUTER_IP[1, 2]) and two hosts connected to it
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# (PEER_IP[1, 2] respectively). The router (in the parent pytest
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# process) will configure netfilterqueue iptables rules and use them
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# to intercept and modify traffic between the two hosts (each of which
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# is implemented in a subprocess).
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#
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# The 'peer' subprocesses communicate with each other over UDP, and
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# with the router parent over a UNIX domain SOCK_SEQPACKET socketpair.
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# Each packet sent from the parent to one peer over the UNIX domain
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# socket will be forwarded to the other peer over UDP. Each packet
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# received over UDP by either of the peers will be forwarded to its
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# parent.
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ROUTER_IP = {1: "172.16.101.1", 2: "172.16.102.1"}
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PEER_IP = {1: "172.16.101.2", 2: "172.16.102.2"}
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def enter_netns() -> None:
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# Create new namespaces of the other types we need
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unshare.unshare(unshare.CLONE_NEWNS | unshare.CLONE_NEWNET)
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# Mount /sys so network tools work
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subprocess.run("/bin/mount -t sysfs sys /sys".split(), check=True)
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# Bind-mount /run so iptables can get its lock
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subprocess.run("/bin/mount -t tmpfs tmpfs /run".split(), check=True)
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# Set up loopback interface
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subprocess.run("/sbin/ip link set lo up".split(), check=True)
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@pytest.hookimpl(tryfirst=True)
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def pytest_runtestloop():
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if os.getuid() != 0:
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# Create a new user namespace for the whole test session
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outer = {"uid": os.getuid(), "gid": os.getgid()}
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unshare.unshare(unshare.CLONE_NEWUSER)
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with open("/proc/self/setgroups", "wb") as fp:
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# This is required since we're unprivileged outside the namespace
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fp.write(b"deny")
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for idtype in ("uid", "gid"):
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with open(f"/proc/self/{idtype}_map", "wb") as fp:
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fp.write(b"0 %d 1" % (outer[idtype],))
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assert os.getuid() == os.getgid() == 0
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# Create a new network namespace for this pytest process
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enter_netns()
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with open("/proc/sys/net/ipv4/ip_forward", "wb") as fp:
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fp.write(b"1\n")
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async def peer_main(idx: int, parent_fd: int) -> None:
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parent = trio.socket.fromfd(
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parent_fd, socket.AF_UNIX, socket.SOCK_SEQPACKET
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)
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# Tell parent we've set up our netns, wait for it to confirm it's
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# created our veth interface
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await parent.send(b"ok")
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assert b"ok" == await parent.recv(4096)
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my_ip = PEER_IP[idx]
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router_ip = ROUTER_IP[idx]
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peer_ip = PEER_IP[3 - idx]
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for cmd in (
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f"ip link set veth0 up",
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f"ip addr add {my_ip}/24 dev veth0",
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f"ip route add default via {router_ip} dev veth0",
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):
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await trio.run_process(
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cmd.split(), capture_stdout=True, capture_stderr=True
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)
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peer = trio.socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
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await peer.bind((my_ip, 0))
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# Tell the parent our port and get our peer's port
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await parent.send(b"%d" % peer.getsockname()[1])
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peer_port = int(await parent.recv(4096))
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await peer.connect((peer_ip, peer_port))
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# Enter the message-forwarding loop
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async def proxy_one_way(src, dest):
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while True:
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try:
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msg = await src.recv(4096)
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except trio.ClosedResourceError:
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return
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if not msg:
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dest.close()
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return
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try:
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await dest.send(msg)
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except BrokenPipeError:
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return
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async with trio.open_nursery() as nursery:
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nursery.start_soon(proxy_one_way, parent, peer)
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nursery.start_soon(proxy_one_way, peer, parent)
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class Harness:
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def __init__(self):
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self._received = {}
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self._conn = {}
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self.failed = False
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async def _run_peer(self, idx: int, *, task_status):
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their_ip = PEER_IP[idx]
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my_ip = ROUTER_IP[idx]
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conn, child_conn = trio.socket.socketpair(socket.AF_UNIX, socket.SOCK_SEQPACKET)
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with conn:
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try:
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process = await trio.open_process(
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[sys.executable, __file__, str(idx), str(child_conn.fileno())],
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stdin=subprocess.DEVNULL,
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pass_fds=[child_conn.fileno()],
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preexec_fn=enter_netns,
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)
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finally:
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child_conn.close()
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assert b"ok" == await conn.recv(4096)
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for cmd in (
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f"ip link add veth{idx} type veth peer netns {process.pid} name veth0",
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f"ip link set veth{idx} up",
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f"ip addr add {my_ip}/24 dev veth{idx}",
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):
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await trio.run_process(cmd.split())
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try:
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await conn.send(b"ok")
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self._conn[idx] = conn
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task_status.started()
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retval = await process.wait()
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except BaseException:
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process.kill()
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with trio.CancelScope(shield=True):
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await process.wait()
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raise
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else:
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if retval != 0:
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raise RuntimeError(
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"peer subprocess exited with code {}".format(retval)
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)
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finally:
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await trio.run_process(f"ip link delete veth{idx}".split())
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async def _manage_peer(self, idx: int, *, task_status):
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async with trio.open_nursery() as nursery:
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await nursery.start(self._run_peer, idx)
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packets_w, packets_r = trio.open_memory_channel(math.inf)
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self._received[idx] = packets_r
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task_status.started()
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async with packets_w:
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while True:
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msg = await self._conn[idx].recv(4096)
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if not msg:
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break
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await packets_w.send(msg)
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@asynccontextmanager
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async def run(self):
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async with trio.open_nursery() as nursery:
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async with trio.open_nursery() as start_nursery:
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start_nursery.start_soon(nursery.start, self._manage_peer, 1)
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start_nursery.start_soon(nursery.start, self._manage_peer, 2)
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# Tell each peer about the other one's port
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await self._conn[2].send(await self._received[1].receive())
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await self._conn[1].send(await self._received[2].receive())
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yield
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self._conn[1].shutdown(socket.SHUT_WR)
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self._conn[2].shutdown(socket.SHUT_WR)
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if not self.failed:
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for idx in (1, 2):
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async for remainder in self._received[idx]:
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raise AssertionError(
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f"Peer {idx} received unexepcted packet {remainder!r}"
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)
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@asynccontextmanager
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async def capture_packets_to(
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self, idx: int, *, queue_num: int = -1, **options
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) -> AsyncIterator["trio.MemoryReceiveChannel[netfilterqueue.Packet]"]:
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packets_w, packets_r = trio.open_memory_channel(math.inf)
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def stash_packet(p):
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p.retain()
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packets_w.send_nowait(p)
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nfq = netfilterqueue.NetfilterQueue()
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if queue_num >= 0:
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nfq.bind(queue_num, stash_packet, **options)
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else:
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for queue_num in range(16):
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try:
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nfq.bind(queue_num, stash_packet, **options)
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break
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except Exception as ex:
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last_error = ex
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else:
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raise RuntimeError(
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"Couldn't bind any netfilter queue number between 0-15"
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)
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try:
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rule = f"-d {PEER_IP[idx]} -j NFQUEUE --queue-num {queue_num}"
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await trio.run_process(f"/sbin/iptables -A FORWARD {rule}".split())
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try:
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async with packets_w, trio.open_nursery() as nursery:
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@nursery.start_soon
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async def listen_for_packets():
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while True:
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await trio.lowlevel.wait_readable(nfq.get_fd())
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nfq.run(block=False)
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yield packets_r
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nursery.cancel_scope.cancel()
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finally:
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await trio.run_process(f"/sbin/iptables -D FORWARD {rule}".split())
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finally:
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nfq.unbind()
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async def expect(self, idx: int, *packets: bytes):
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for expected in packets:
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with trio.move_on_after(5) as scope:
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received = await self._received[idx].receive()
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if scope.cancelled_caught:
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self.failed = True
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raise AssertionError(
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f"Timeout waiting for peer {idx} to receive {expected!r}"
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)
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if received != expected:
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self.failed = True
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raise AssertionError(
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f"Expected peer {idx} to receive {expected!r} but it "
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f"received {received!r}"
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)
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async def send(self, idx: int, *packets: bytes):
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for packet in packets:
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await self._conn[3 - idx].send(packet)
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@pytest.fixture
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async def harness() -> Harness:
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h = Harness()
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async with h.run():
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yield h
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if __name__ == "__main__":
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trio.run(peer_main, int(sys.argv[1]), int(sys.argv[2]))
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