Synnefo

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"""

Script is called when an interface changes. For the time being we only support

one subnet and one public IP.

Logic:

Whenever this script is called, one of our nics changed, so flush everything.

If the nic is public create the rules for the private net given in the config

file

Else do nothing

"""

import iptc

import netifaces

import sys

import IPy

import ConfigParser

import logging

import logging.handlers

CONFIG_FILE = 'file.conf'

def flush(table_name, chain_name):

    """

    Flushes the chain chain_name of table table_name

    iptables -F chain_name -t table_name

    """

    table = iptc.Table(getattr(iptc.Table, table_name))

    table.flush_entries(chain_name)

def create_dnat(cidr, ports, start_port, step, public_ip):

    """

    Create the dnat rules

    iptables -t nat -A PREROUTING -p tcp -d public_ip --dport sport \

        -j DNAT --to-destination cidr:ports

    """

    i = 0

    for ip in IPy.IP(cidr):

        j = 0

        for sport in ports:

            rule = iptc.Rule()

            rule.dst = public_ip

            rule.protocol = "tcp"

            match = iptc.Match(rule, "tcp")

            port = int(start_port) + j*int(step) + i

            match.dport = str(port)

            rule.add_match(match)

            target = iptc.Target(rule, "DNAT")

            rule.target = target

            rule.target.to_destination = "%s:%s" % (ip, sport)

            chain = iptc.Chain(iptc.Table(iptc.Table.NAT), "PREROUTING")

            chain.insert_rule(rule)

            j = j + 1

        i = i + 1

def create_snat(public_ip, private_net, public_iface):

    """

    Creates the snat rules

    iptables -t nat -A POSTROUTING -o public_iface -s private_net \

        ! -d private_net -j SNAT --to-source public_ip

    """

    chain = iptc.Chain(iptc.Table(iptc.Table.NAT), "POSTROUTING")

    rule = iptc.Rule()

    private_net = "%s" % IPy.IP(private_net).strNormal(2)

    rule.src = private_net

    rule.dst = "!%s" % private_net

    rule.out_interface = public_iface

    target = iptc.Target(rule, "SNAT")

    target.to_source = public_ip

    rule.target = target

    chain.insert_rule(rule)

def create_states(private_net, public_iface, private_iface):

    """

    Creates rules for the established connections

    iptables -A FORWARD -i public_iface -o private_iface ! -s private_net \

        -d private_net -m state --state ESTABLISHED,RELATED

    """

    chain = iptc.Chain(iptc.Table(iptc.Table.FILTER), "FORWARD")

    rule = iptc.Rule()

    private_net = "%s" % IPy.IP(private_net).strNormal(2)

    rule.src = "!%s" % private_net

    rule.dst = private_net

    rule.out_interface = private_iface

    rule.in_interface = public_iface

    match = iptc.Match(rule, 'state')

    match.state = "ESTABLISHED,RELATED"

    rule.add_match(match)

    target = iptc.Target(rule, "ACCEPT")

    rule.target = target

    chain.insert_rule(rule)

def nic_info(interface):

    """

    Returns the IP and ip type (PUBLIC/PRIVATE) of interface

    """

    nic = dict()

    nic['ip'] = netifaces.ifaddresses(interface)[netifaces.AF_INET][0]['addr']

    nic['ip_type'] = IPy.IP(nic['ip']).iptype()

    return nic

def parse_config(filename):

    config = ConfigParser.ConfigParser()

    config.read(filename)

    return config

def create_remote_logger(host, url, method):

    logger = logging.getLogger('snf-router')

    logger.setLevel(logging.INFO)

    #http_handler = logging.handlers.HTTPHandler(host, url, method)

    http_handler = logging.handlers.WatchedFileHandler("test.log")

    formatter = logging.Formatter("%(asctime)s - %(message)s")

    http_handler.setFormatter(formatter)

    logger.addHandler(http_handler)

    return logger

def allow_ssh():

    chain = iptc.Chain(iptc.Table(iptc.Table.FILTER), "INPUT")

    rule = iptc.Rule()

    rule.protocol = "tcp"

    match = iptc.Match(rule, "tcp")

    match.dport = "22"

    rule.add_match(match)

    target = iptc.Target(rule, "ACCEPT")

    rule.target = target

    chain.insert_rule(rule)

    chain = iptc.Chain(iptc.Table(iptc.Table.FILTER), "OUTPUT")

    rule = iptc.Rule()

    rule.protocol = "tcp"

    match = iptc.Match(rule, "tcp")

    match.sport = "22"

    rule.add_match(match)

    target = iptc.Target(rule, "ACCEPT")

    rule.target = target

    chain.insert_rule(rule)

def set_policy(table, chain, policy):

    cur_table = iptc.Table(getattr(iptc.Table, table))

    cur_chain = iptc.Chain(cur_table, chain)

    cur_chain.set_policy(policy)

def get_public_iface():

    public_iface = ''

    for iface in netifaces.interfaces():

        nic = nic_info(iface)

        if nic['ip_type'] == 'PUBLIC':

            public_iface = iface

            break

    return public_iface

def main():

    #read config file

    config = parse_config(CONFIG_FILE)

    start_port = config.get("private-network", "start_port")

    step = config.get("private-network", "step")

    private_cidr = config.get("private-network", "cidr")

    private_iface = config.get("private-network", "iface")

    nic = nic_info(interface_name)

    interface_name = sys.argv[1]

    action = sys.argv[2]

    #create logger

    logger = create_remote_logger(config.get('log', 'host'),

                                  config.get('log', 'url'),

                                  config.get('log', 'method'))

    #logger.info(nic['ip_type'] + " " + sys.argv[1] + " " + sys.argv[2])

    logger.info("%s %s %s" % (nic['ip_type'], action, interface_name))

    if action == 'up' and nic['ip_type'] == "PUBLIC":

        #flush the old rules

        flush("NAT", "PREROUTING")

        flush("NAT", "POSTROUTING")

        flush("FILTER", "FORWARD")

        #set policy

        #set_policy("FILTER", "FORWARD", config.get('policy', 'FORWARD'))

        #set_policy("FILTER", "OUTPUT", config.get('policy', 'OUTPUT'))

        #set_policy("FILTER", "INPUT", config.get('policy', 'INPUT'))

        # create dnat

        create_dnat(private_cidr,

                    config.get("private-network", "ports").split(","),

                    start_port, step, nic["ip"])

        # create snat

        create_snat(nic['ip'], private_cidr, interface_name)

        create_states(private_cidr, interface_name, private_iface)

if __name__ == "__main__":

    main()