path: root/cloudinit/net/dhcp.py

# Copyright (C) 2017 Canonical Ltd.
#
# Author: Chad Smith <chad.smith@canonical.com>
#
# This file is part of cloud-init. See LICENSE file for license information.

import logging
import os
import re
import signal
import time
from io import StringIO
from typing import Any, Dict

import configobj

from cloudinit import subp, temp_utils, util
from cloudinit.net import (
    EphemeralIPv4Network,
    find_fallback_nic,
    get_devicelist,
    has_url_connectivity,
)
from cloudinit.net.network_state import mask_and_ipv4_to_bcast_addr as bcip

LOG = logging.getLogger(__name__)

NETWORKD_LEASES_DIR = "/run/systemd/netif/leases"


class InvalidDHCPLeaseFileError(Exception):
    """Raised when parsing an empty or invalid dhcp.leases file.

    Current uses are DataSourceAzure and DataSourceEc2 during ephemeral
    boot to scrape metadata.
    """


class NoDHCPLeaseError(Exception):
    """Raised when unable to get a DHCP lease."""


class EphemeralDHCPv4(object):
    def __init__(
        self,
        iface=None,
        connectivity_url_data: Dict[str, Any] = None,
        dhcp_log_func=None,
    ):
        self.iface = iface
        self._ephipv4 = None
        self.lease = None
        self.dhcp_log_func = dhcp_log_func
        self.connectivity_url_data = connectivity_url_data

    def __enter__(self):
        """Setup sandboxed dhcp context, unless connectivity_url can already be
        reached."""
        if self.connectivity_url_data:
            if has_url_connectivity(self.connectivity_url_data):
                LOG.debug(
                    "Skip ephemeral DHCP setup, instance has connectivity"
                    " to %s",
                    self.connectivity_url_data,
                )
                return
        return self.obtain_lease()

    def __exit__(self, excp_type, excp_value, excp_traceback):
        """Teardown sandboxed dhcp context."""
        self.clean_network()

    def clean_network(self):
        """Exit _ephipv4 context to teardown of ip configuration performed."""
        if self.lease:
            self.lease = None
        if not self._ephipv4:
            return
        self._ephipv4.__exit__(None, None, None)

    def obtain_lease(self):
        """Perform dhcp discovery in a sandboxed environment if possible.

        @return: A dict representing dhcp options on the most recent lease
            obtained from the dhclient discovery if run, otherwise an error
            is raised.

        @raises: NoDHCPLeaseError if no leases could be obtained.
        """
        if self.lease:
            return self.lease
        try:
            leases = maybe_perform_dhcp_discovery(
                self.iface, self.dhcp_log_func
            )
        except InvalidDHCPLeaseFileError as e:
            raise NoDHCPLeaseError() from e
        if not leases:
            raise NoDHCPLeaseError()
        self.lease = leases[-1]
        LOG.debug(
            "Received dhcp lease on %s for %s/%s",
            self.lease["interface"],
            self.lease["fixed-address"],
            self.lease["subnet-mask"],
        )
        nmap = {
            "interface": "interface",
            "ip": "fixed-address",
            "prefix_or_mask": "subnet-mask",
            "broadcast": "broadcast-address",
            "static_routes": [
                "rfc3442-classless-static-routes",
                "classless-static-routes",
            ],
            "router": "routers",
        }
        kwargs = self.extract_dhcp_options_mapping(nmap)
        if not kwargs["broadcast"]:
            kwargs["broadcast"] = bcip(kwargs["prefix_or_mask"], kwargs["ip"])
        if kwargs["static_routes"]:
            kwargs["static_routes"] = parse_static_routes(
                kwargs["static_routes"]
            )
        if self.connectivity_url_data:
            kwargs["connectivity_url_data"] = self.connectivity_url_data
        ephipv4 = EphemeralIPv4Network(**kwargs)
        ephipv4.__enter__()
        self._ephipv4 = ephipv4
        return self.lease

    def extract_dhcp_options_mapping(self, nmap):
        result = {}
        for internal_reference, lease_option_names in nmap.items():
            if isinstance(lease_option_names, list):
                self.get_first_option_value(
                    internal_reference, lease_option_names, result
                )
            else:
                result[internal_reference] = self.lease.get(lease_option_names)
        return result

    def get_first_option_value(
        self, internal_mapping, lease_option_names, result
    ):
        for different_names in lease_option_names:
            if not result.get(internal_mapping):
                result[internal_mapping] = self.lease.get(different_names)


def maybe_perform_dhcp_discovery(nic=None, dhcp_log_func=None):
    """Perform dhcp discovery if nic valid and dhclient command exists.

    If the nic is invalid or undiscoverable or dhclient command is not found,
    skip dhcp_discovery and return an empty dict.

    @param nic: Name of the network interface we want to run dhclient on.
    @param dhcp_log_func: A callable accepting the dhclient output and error
        streams.
    @return: A list of dicts representing dhcp options for each lease obtained
        from the dhclient discovery if run, otherwise an empty list is
        returned.
    """
    if nic is None:
        nic = find_fallback_nic()
        if nic is None:
            LOG.debug("Skip dhcp_discovery: Unable to find fallback nic.")
            return []
    elif nic not in get_devicelist():
        LOG.debug(
            "Skip dhcp_discovery: nic %s not found in get_devicelist.", nic
        )
        return []
    dhclient_path = subp.which("dhclient")
    if not dhclient_path:
        LOG.debug("Skip dhclient configuration: No dhclient command found.")
        return []
    with temp_utils.tempdir(
        rmtree_ignore_errors=True, prefix="cloud-init-dhcp-", needs_exe=True
    ) as tdir:
        # Use /var/tmp because /run/cloud-init/tmp is mounted noexec
        return dhcp_discovery(dhclient_path, nic, tdir, dhcp_log_func)


def parse_dhcp_lease_file(lease_file):
    """Parse the given dhcp lease file for the most recent lease.

    Return a list of dicts of dhcp options. Each dict contains key value pairs
    a specific lease in order from oldest to newest.

    @raises: InvalidDHCPLeaseFileError on empty of unparseable leasefile
        content.
    """
    lease_regex = re.compile(r"lease {(?P<lease>.*?)}\n", re.DOTALL)
    dhcp_leases = []
    lease_content = util.load_file(lease_file)
    if len(lease_content) == 0:
        raise InvalidDHCPLeaseFileError(
            "Cannot parse empty dhcp lease file {0}".format(lease_file)
        )
    for lease in lease_regex.findall(lease_content):
        lease_options = []
        for line in lease.split(";"):
            # Strip newlines, double-quotes and option prefix
            line = line.strip().replace('"', "").replace("option ", "")
            if not line:
                continue
            lease_options.append(line.split(" ", 1))
        dhcp_leases.append(dict(lease_options))
    if not dhcp_leases:
        raise InvalidDHCPLeaseFileError(
            "Cannot parse dhcp lease file {0}. No leases found".format(
                lease_file
            )
        )
    return dhcp_leases


def dhcp_discovery(dhclient_cmd_path, interface, cleandir, dhcp_log_func=None):
    """Run dhclient on the interface without scripts or filesystem artifacts.

    @param dhclient_cmd_path: Full path to the dhclient used.
    @param interface: Name of the network inteface on which to dhclient.
    @param cleandir: The directory from which to run dhclient as well as store
        dhcp leases.
    @param dhcp_log_func: A callable accepting the dhclient output and error
        streams.

    @return: A list of dicts of representing the dhcp leases parsed from the
        dhcp.leases file or empty list.
    """
    LOG.debug("Performing a dhcp discovery on %s", interface)

    # XXX We copy dhclient out of /sbin/dhclient to avoid dealing with strict
    # app armor profiles which disallow running dhclient -sf <our-script-file>.
    # We want to avoid running /sbin/dhclient-script because of side-effects in
    # /etc/resolv.conf any any other vendor specific scripts in
    # /etc/dhcp/dhclient*hooks.d.
    sandbox_dhclient_cmd = os.path.join(cleandir, "dhclient")
    util.copy(dhclient_cmd_path, sandbox_dhclient_cmd)
    pid_file = os.path.join(cleandir, "dhclient.pid")
    lease_file = os.path.join(cleandir, "dhcp.leases")

    # In some cases files in /var/tmp may not be executable, launching dhclient
    # from there will certainly raise 'Permission denied' error. Try launching
    # the original dhclient instead.
    if not os.access(sandbox_dhclient_cmd, os.X_OK):
        sandbox_dhclient_cmd = dhclient_cmd_path

    # ISC dhclient needs the interface up to send initial discovery packets.
    # Generally dhclient relies on dhclient-script PREINIT action to bring the
    # link up before attempting discovery. Since we are using -sf /bin/true,
    # we need to do that "link up" ourselves first.
    subp.subp(["ip", "link", "set", "dev", interface, "up"], capture=True)
    cmd = [
        sandbox_dhclient_cmd,
        "-1",
        "-v",
        "-lf",
        lease_file,
        "-pf",
        pid_file,
        interface,
        "-sf",
        "/bin/true",
    ]
    out, err = subp.subp(cmd, capture=True)

    # Wait for pid file and lease file to appear, and for the process
    # named by the pid file to daemonize (have pid 1 as its parent). If we
    # try to read the lease file before daemonization happens, we might try
    # to read it before the dhclient has actually written it. We also have
    # to wait until the dhclient has become a daemon so we can be sure to
    # kill the correct process, thus freeing cleandir to be deleted back
    # up the callstack.
    missing = util.wait_for_files(
        [pid_file, lease_file], maxwait=5, naplen=0.01
    )
    if missing:
        LOG.warning(
            "dhclient did not produce expected files: %s",
            ", ".join(os.path.basename(f) for f in missing),
        )
        return []

    ppid = "unknown"
    daemonized = False
    for _ in range(0, 1000):
        pid_content = util.load_file(pid_file).strip()
        try:
            pid = int(pid_content)
        except ValueError:
            pass
        else:
            ppid = util.get_proc_ppid(pid)
            if ppid == 1:
                LOG.debug("killing dhclient with pid=%s", pid)
                os.kill(pid, signal.SIGKILL)
                daemonized = True
                break
        time.sleep(0.01)

    if not daemonized:
        LOG.error(
            "dhclient(pid=%s, parentpid=%s) failed to daemonize after %s "
            "seconds",
            pid_content,
            ppid,
            0.01 * 1000,
        )
    if dhcp_log_func is not None:
        dhcp_log_func(out, err)
    return parse_dhcp_lease_file(lease_file)


def networkd_parse_lease(content):
    """Parse a systemd lease file content as in /run/systemd/netif/leases/

    Parse this (almost) ini style file even though it says:
      # This is private data. Do not parse.

    Simply return a dictionary of key/values."""

    return dict(configobj.ConfigObj(StringIO(content), list_values=False))


def networkd_load_leases(leases_d=None):
    """Return a dictionary of dictionaries representing each lease
    found in lease_d.i

    The top level key will be the filename, which is typically the ifindex."""

    if leases_d is None:
        leases_d = NETWORKD_LEASES_DIR

    ret = {}
    if not os.path.isdir(leases_d):
        return ret
    for lfile in os.listdir(leases_d):
        ret[lfile] = networkd_parse_lease(
            util.load_file(os.path.join(leases_d, lfile))
        )
    return ret


def networkd_get_option_from_leases(keyname, leases_d=None):
    if leases_d is None:
        leases_d = NETWORKD_LEASES_DIR
    leases = networkd_load_leases(leases_d=leases_d)
    for _ifindex, data in sorted(leases.items()):
        if data.get(keyname):
            return data[keyname]
    return None


def parse_static_routes(rfc3442):
    """parse rfc3442 format and return a list containing tuple of strings.

    The tuple is composed of the network_address (including net length) and
    gateway for a parsed static route.  It can parse two formats of rfc3442,
    one from dhcpcd and one from dhclient (isc).

    @param rfc3442: string in rfc3442 format (isc or dhcpd)
    @returns: list of tuple(str, str) for all valid parsed routes until the
              first parsing error.

    E.g.
    sr=parse_static_routes("32,169,254,169,254,130,56,248,255,0,130,56,240,1")
    sr=[
        ("169.254.169.254/32", "130.56.248.255"), ("0.0.0.0/0", "130.56.240.1")
    ]

    sr2 = parse_static_routes("24.191.168.128 192.168.128.1,0 192.168.128.1")
    sr2 = [
        ("191.168.128.0/24", "192.168.128.1"), ("0.0.0.0/0", "192.168.128.1")
    ]

    Python version of isc-dhclient's hooks:
       /etc/dhcp/dhclient-exit-hooks.d/rfc3442-classless-routes
    """
    # raw strings from dhcp lease may end in semi-colon
    rfc3442 = rfc3442.rstrip(";")
    tokens = [tok for tok in re.split(r"[, .]", rfc3442) if tok]
    static_routes = []

    def _trunc_error(cidr, required, remain):
        msg = (
            "RFC3442 string malformed.  Current route has CIDR of %s "
            "and requires %s significant octets, but only %s remain. "
            "Verify DHCP rfc3442-classless-static-routes value: %s"
            % (cidr, required, remain, rfc3442)
        )
        LOG.error(msg)

    current_idx = 0
    for idx, tok in enumerate(tokens):
        if idx < current_idx:
            continue
        net_length = int(tok)
        if net_length in range(25, 33):
            req_toks = 9
            if len(tokens[idx:]) < req_toks:
                _trunc_error(net_length, req_toks, len(tokens[idx:]))
                return static_routes
            net_address = ".".join(tokens[idx + 1 : idx + 5])
            gateway = ".".join(tokens[idx + 5 : idx + req_toks])
            current_idx = idx + req_toks
        elif net_length in range(17, 25):
            req_toks = 8
            if len(tokens[idx:]) < req_toks:
                _trunc_error(net_length, req_toks, len(tokens[idx:]))
                return static_routes
            net_address = ".".join(tokens[idx + 1 : idx + 4] + ["0"])
            gateway = ".".join(tokens[idx + 4 : idx + req_toks])
            current_idx = idx + req_toks
        elif net_length in range(9, 17):
            req_toks = 7
            if len(tokens[idx:]) < req_toks:
                _trunc_error(net_length, req_toks, len(tokens[idx:]))
                return static_routes
            net_address = ".".join(tokens[idx + 1 : idx + 3] + ["0", "0"])
            gateway = ".".join(tokens[idx + 3 : idx + req_toks])
            current_idx = idx + req_toks
        elif net_length in range(1, 9):
            req_toks = 6
            if len(tokens[idx:]) < req_toks:
                _trunc_error(net_length, req_toks, len(tokens[idx:]))
                return static_routes
            net_address = ".".join(tokens[idx + 1 : idx + 2] + ["0", "0", "0"])
            gateway = ".".join(tokens[idx + 2 : idx + req_toks])
            current_idx = idx + req_toks
        elif net_length == 0:
            req_toks = 5
            if len(tokens[idx:]) < req_toks:
                _trunc_error(net_length, req_toks, len(tokens[idx:]))
                return static_routes
            net_address = "0.0.0.0"
            gateway = ".".join(tokens[idx + 1 : idx + req_toks])
            current_idx = idx + req_toks
        else:
            LOG.error(
                'Parsed invalid net length "%s".  Verify DHCP '
                "rfc3442-classless-static-routes value.",
                net_length,
            )
            return static_routes

        static_routes.append(("%s/%s" % (net_address, net_length), gateway))

    return static_routes


# vi: ts=4 expandtab