3proxy/tests/cases/parent_ports.py

"""extport and intport: binding the local side of a connection to a range.

Access rules accumulate until "flush": without it an earlier "allow *"
matches first and the rule carrying the range is never reached.
"""

from harness import int_field


def _windows():
    """Pick port windows this platform will actually honour.

    On Linux the kernel applies IP_LOCAL_PORT_RANGE only within
    net.ipv4.ip_local_port_range; a window outside it is ignored and an
    ordinary ephemeral port is used, so a fixed low window would be
    measuring the kernel's own choice rather than the setting.

    Everywhere else the range is honoured by binding a port out of it at
    random, ten times before giving up and letting the system choose. A port
    which carried a connection a moment ago cannot be bound again while it
    waits out its close - four minutes of it on Windows - so the window has
    to be wide enough that ten tries do not all land on one. The window the
    kernel picks from on Linux needs no such room, since it skips them.
    """
    try:
        with open("/proc/sys/net/ipv4/ip_local_port_range") as fp:
            low, high = (int(part) for part in fp.read().split()[:2])
    except (OSError, ValueError):
        return (21400, 21899), (22000, 22499)
    base = low + 1000 if low + 1150 <= high else low
    return (base, base + 49), (base + 100, base + 149)


(LOW, HIGH), (ILOW, IHIGH) = _windows()

# Privileged ports: the kernel ignores such a range on Linux, since it is
# outside net.ipv4.ip_local_port_range, and binding them fails outright
# without privileges. Either way nothing in the range can be taken, which
# is the case the fallback exists for.
UNHONOURED = (1, 99)


def run(t):
    srv = t.free_port()
    prx = t.free_port()
    sks = t.free_port()
    meth = t.free_port()

    t.start("parent_ports", f"""
        log
        auth iponly
        allow *
        http echo * /echo**
        httpsrv -p{srv}

        # every outgoing connection binds inside the range
        flush
        auth iponly
        allow *
        parent 1000 extport 0.0.0.0 {LOW}-{HIGH}
        proxy -p{prx}

        # the range applies only to CONNECT: an HTTP proxy CONNECT is
        # HTTP_CONNECT, the bare CONNECT operation being the SOCKS one
        flush
        auth iponly
        allow * * * * HTTP_CONNECT
        parent 1000 extport 0.0.0.0 {LOW}-{HIGH}
        allow *
        proxy -p{meth}

        # socks, for the same setting on another service
        flush
        auth iponly
        allow *
        parent 1000 extport 0.0.0.0 {LOW}-{HIGH}
        socks -p{sks}
    """, ports=[srv, prx, sks, meth])

    origin = f"http://127.0.0.1:{srv}"
    proxy = f"127.0.0.1:{prx}"

    # --- extport ---------------------------------------------------------
    # the origin reports the source port it actually saw
    port = int_field(t.http(origin + "/echo", proxy=proxy), "peer.port")
    t.in_range(port, LOW, HIGH, "the outgoing connection binds inside the range")

    seen = []
    for _ in range(5):
        seen.append(int_field(t.http(origin + "/echo", proxy=proxy), "peer.port"))
    outside = [p for p in seen if p is None or not LOW <= p <= HIGH]
    t.eq([], outside, "repeated connections all bind inside the range")

    port = int_field(t.socks_http(f"127.0.0.1:{sks}", origin + "/echo"),
                     "peer.port")
    t.in_range(port, LOW, HIGH,
               "socks binds the outgoing connection inside the range")

    # --- per-method scoping ------------------------------------------------
    method_proxy = f"127.0.0.1:{meth}"
    port = int_field(t.http(origin + "/echo", proxy=method_proxy, tunnel=True),
                     "peer.port")
    t.in_range(port, LOW, HIGH, "CONNECT uses the range its rule sets")

    # a plain GET matches the later rule, which sets no range
    port = int_field(t.http(origin + "/echo", proxy=method_proxy), "peer.port")
    t.not_in_range(port, LOW, HIGH,
                   "a method outside that rule keeps an ephemeral port")

    # --- a range the platform cannot honour --------------------------------
    # Linux ignores a range outside net.ipv4.ip_local_port_range, and any
    # platform can run out of free ports in a range. Either way the
    # connection falls back to an ephemeral port instead of failing.
    unhonoured = t.free_port()
    t.start("parent_unhonoured", f"""
        log
        flush
        auth iponly
        allow *
        parent 1000 extport 0.0.0.0 {UNHONOURED[0]}-{UNHONOURED[1]}
        proxy -p{unhonoured}
    """, ports=[unhonoured])
    r = t.http(origin + "/echo", proxy=f"127.0.0.1:{unhonoured}")
    t.eq(200, r.status, "a range the platform cannot honour still connects")
    t.ne(None, int_field(r, "peer.port"),
         "the connection still has a source port")

    # --- intport -----------------------------------------------------------
    # A UDP association allocates its socket after the destination is known,
    # so the range has to be applied when the rule matches rather than when
    # the chain is walked.
    udps = t.free_port()
    t.start("parent_intport", f"""
        log
        flush
        auth iponly
        allow *
        parent 1000 intport 0.0.0.0 {ILOW}-{IHIGH}
        socks -p{udps}
    """, ports=[udps])
    t.in_range(t.socks_udp_associate(udps), ILOW, IHIGH,
               "UDP ASSOCIATE binds inside the internal range")

    # and the association still carries traffic while bound in the range
    echo = t.udp_echo()
    reply, bound = t.socks_udp(f"127.0.0.1:{udps}", "127.0.0.1", echo, b"data")
    t.eq(b"echo:data", reply, "a range-bound association still relays")
    t.in_range(bound, ILOW, IHIGH, "and the port it relays from is in the range")

    # without a range the association still works, on an ephemeral port
    udps2 = t.free_port()
    t.start("parent_intport_none", f"""
        log
        flush
        auth iponly
        allow *
        socks -p{udps2}
    """, ports=[udps2])
    t.ne(None, t.socks_udp_associate(udps2),
         "UDP ASSOCIATE works without a range")

    # --- configuration errors ------------------------------------------------
    dead = t.free_port()
    t.contains(t.run_config("badaddr", f"""
        log
        allow *
        parent 1000 extport 127.0.0.1 {LOW}-{HIGH}
        proxy -p{dead}
    """), "requires 0.0.0.0", "a non-zero address with extport is rejected")

    t.contains(t.run_config("badrange", f"""
        log
        allow *
        parent 1000 extport 0.0.0.0 notaport
        proxy -p{dead}
    """), "bad port range", "a malformed range is rejected")

    t.contains(t.run_config("badorder", f"""
        log
        allow *
        parent 1000 extport 0.0.0.0 {HIGH}-{LOW}
        proxy -p{dead}
    """), "bad port range", "a reversed range is rejected")