python-netfilterqueue/tests/test_basic.py

import struct
import trio
import trio.testing
import pytest
import signal
import sys

from netfilterqueue import NetfilterQueue


async def test_comms_without_queue(harness):
    await harness.send(2, b"hello", b"world")
    await harness.expect(2, b"hello", b"world")
    await harness.send(1, b"it works?")
    await harness.expect(1, b"it works?")


async def test_queue_dropping(harness):
    async def drop(packets, msg):
        async for packet in packets:
            if packet.get_payload()[28:] == msg:
                packet.drop()
            else:
                packet.accept()

    async with trio.open_nursery() as nursery:
        async with harness.capture_packets_to(2) as p2, harness.capture_packets_to(
            1
        ) as p1:
            nursery.start_soon(drop, p2, b"two")
            nursery.start_soon(drop, p1, b"one")

            await harness.send(2, b"one", b"two", b"three")
            await harness.send(1, b"one", b"two", b"three")
            await harness.expect(2, b"one", b"three")
            await harness.expect(1, b"two", b"three")

        # Once we stop capturing, everything gets through again:
        await harness.send(2, b"one", b"two", b"three")
        await harness.send(1, b"one", b"two", b"three")
        await harness.expect(2, b"one", b"two", b"three")
        await harness.expect(1, b"one", b"two", b"three")


async def test_rewrite_reorder(harness):
    async def munge(packets):
        def set_udp_payload(p, msg):
            data = bytearray(p.get_payload())
            old_len = len(data) - 28
            if len(msg) != old_len:
                data[2:4] = struct.pack(">H", len(msg) + 28)
                data[24:26] = struct.pack(">H", len(msg) + 8)
                # Recompute checksum too
                data[10:12] = b"\x00\x00"
                words = struct.unpack(">10H", data[:20])
                cksum = sum(words)
                while cksum >> 16:
                    cksum = (cksum & 0xFFFF) + (cksum >> 16)
                data[10:12] = struct.pack(">H", cksum ^ 0xFFFF)
            # Clear UDP checksum and set payload
            data[28:] = msg
            data[26:28] = b"\x00\x00"
            p.set_payload(bytes(data))

        async for packet in packets:
            payload = packet.get_payload()[28:]
            if payload == b"one":
                set_udp_payload(packet, b"numero uno")
                assert b"numero uno" == packet.get_payload()[28:]
                packet.accept()
            elif payload == b"two":
                two = packet
            elif payload == b"three":
                set_udp_payload(two, b"TWO")
                packet.accept()
                two.accept()
            else:
                packet.accept()

    async with trio.open_nursery() as nursery:
        async with harness.capture_packets_to(2) as p2:
            nursery.start_soon(munge, p2)
            await harness.send(2, b"one", b"two", b"three", b"four")
            await harness.expect(2, b"numero uno", b"three", b"TWO", b"four")


async def test_errors(harness):
    with pytest.warns(RuntimeWarning, match="rcvbuf limit is") as record:
        async with harness.capture_packets_to(2, sock_len=2 ** 30):
            pass
    assert record[0].filename.endswith("conftest.py")

    async with harness.capture_packets_to(2, queue_num=0):
        with pytest.raises(OSError, match="Failed to create queue"):
            async with harness.capture_packets_to(2, queue_num=0):
                pass

    nfq = NetfilterQueue()
    nfq.bind(1, lambda p: None, sock_len=131072)
    with pytest.raises(RuntimeError, match="A queue is already bound"):
        nfq.bind(2, lambda p: None, sock_len=131072)


async def test_unretained(harness):
    # Capture packets without retaining -> can't access payload
    async with harness.capture_packets_to(2, trio.MemorySendChannel.send_nowait) as chan:
        await harness.send(2, b"one", b"two")
        accept = True
        async for p in chan:
            with pytest.raises(RuntimeError, match="Payload data is no longer available"):
                p.get_payload()
            # Can still issue verdicts though
            if accept:
                p.accept()
                accept = False
            else:
                break

    with pytest.raises(RuntimeError, match="Parent queue has already been unbound"):
        p.drop()
    await harness.expect(2, b"one")


async def test_cb_exception(harness):
    pkt = None

    def cb(channel, p):
        nonlocal pkt
        pkt = p
        raise ValueError("test")

    # Error raised within run():
    with pytest.raises(ValueError, match="test"):
        async with harness.capture_packets_to(2, cb):
            await harness.send(2, b"boom")
            with trio.fail_after(1):
                try:
                    await trio.sleep_forever()
                finally:
                    # At this point the error has been raised (since we were
                    # cancelled) but the queue is still open. We shouldn't
                    # be able to access the payload, since we didn't retain(),
                    # but verdicts should otherwise work.
                    with pytest.raises(RuntimeError, match="Payload data is no longer"):
                        pkt.get_payload()
                    pkt.accept()

    await harness.expect(2, b"boom")

    with pytest.raises(RuntimeError, match="Verdict already given for this packet"):
        pkt.drop()


async def test_cb_exception_during_unbind(harness, capsys):
    pkt = None

    def cb(channel, p):
        nonlocal pkt
        pkt = p
        raise ValueError("test")

    if sys.version_info >= (3, 8):
        from _pytest.unraisableexception import catch_unraisable_exception
    else:
        from contextlib import contextmanager

        @contextmanager
        def catch_unraisable_exception():
            pass

    with catch_unraisable_exception() as unraise, trio.CancelScope() as cscope:
        async with harness.capture_packets_to(2, cb):
            # Cancel the task that reads from netfilter:
            cscope.cancel()
            with trio.CancelScope(shield=True):
                await trio.testing.wait_all_tasks_blocked()
                # Now actually send the packet and wait for the report to appear
                # (hopefully)
                await harness.send(2, b"boom boom")
                await trio.sleep(0.5)
            # Exiting the block calls unbind() and raises the exception in the cb.
            # It gets caught and discarded as unraisable.

        if unraise:
            assert unraise.unraisable
            assert unraise.unraisable.object == "netfilterqueue callback during unbind"
            assert unraise.unraisable.exc_type is ValueError
            assert str(unraise.unraisable.exc_value) == "test"

    if not unraise:
        assert "Exception ignored in: 'netfilterqueue callback" in capsys.readouterr().err

    with pytest.raises(RuntimeError, match="Payload data is no longer available"):
        pkt.get_payload()
    with pytest.raises(RuntimeError, match="Parent queue has already been unbound"):
        pkt.drop()


def test_signal():
    nfq = NetfilterQueue()
    nfq.bind(1, lambda p: None, sock_len=131072)

    def raise_alarm(sig, frame):
        raise KeyboardInterrupt("brrrrrring!")

    old_handler = signal.signal(signal.SIGALRM, raise_alarm)
    old_timer = signal.setitimer(signal.ITIMER_REAL, 0.5, 0)
    try:
        with pytest.raises(KeyboardInterrupt, match="brrrrrring!") as exc_info:
            nfq.run()
        assert any("NetfilterQueue.run" in line.name for line in exc_info.traceback)
    finally:
        signal.setitimer(signal.ITIMER_REAL, *old_timer)
        signal.signal(signal.SIGALRM, old_handler)