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"""Defines helpful decoders that can be used to decode information from the flows. A decoder is generally a callable that accepts a string and returns the value object. """ import json import netaddr import re class Decoder(object): """Base class for all decoder classes.""" def to_json(self): raise NotImplementedError() def decode_default(value): """Default decoder. It tries to convert into an integer value and, if it fails, just returns the string. """ try: return int(value, 0) except ValueError: return value def decode_flag(value): """Decode a flag. It's existence is just flagged by returning True.""" return True def decode_int(value): """Integer decoder. Both base10 and base16 integers are supported. Used for fields such as: n_bytes=34 metadata=0x4 """ return int(value, 0) def decode_time(value): """Time decoder. Used for fields such as: duration=1234.123s """ if value == "never": return value time_str = value.rstrip("s") return float(time_str) class IntMask(Decoder): """Base class for Integer Mask decoder classes. It supports decoding a value/mask pair. The class has to be derived, and the size attribute must be set. """ size = None # Size in bits. def __init__(self, string): if not self.size: raise NotImplementedError( "IntMask should be derived and size should be fixed" ) parts = string.split("/") if len(parts) > 1: self._value = int(parts[0], 0) self._mask = int(parts[1], 0) if self._mask.bit_length() > self.size: raise ValueError( "Integer mask {} is bigger than size {}".format( self._mask, self.size ) ) else: self._value = int(parts[0], 0) self._mask = self.max_mask() if self._value.bit_length() > self.size: raise ValueError( "Integer value {} is bigger than size {}".format( self._value, self.size ) ) @property def value(self): return self._value @property def mask(self): return self._mask def max_mask(self): return 2 ** self.size - 1 def fully(self): """Returns True if it's fully masked.""" return self._mask == self.max_mask() def __str__(self): if self.fully(): return str(self._value) else: return "{}/{}".format(hex(self._value), hex(self._mask)) def __repr__(self): return "%s('%s')" % (self.__class__.__name__, self) def __eq__(self, other): """Equality operator. Both value and mask must be the same for the comparison to result True. This can be used to implement filters that expect a specific mask, e.g: ct.state = 0x1/0xff. Args: other (IntMask): Another IntMask to compare against. Returns: True if the other IntMask is the same as this one. """ if isinstance(other, IntMask): return self.value == other.value and self.mask == other.mask elif isinstance(other, int): return self.value == other and self.mask == self.max_mask() else: raise ValueError("Cannot compare against ", other) def __contains__(self, other): """Contains operator. Args: other (int or IntMask): Another integer or fully-masked IntMask to compare against. Returns: True if the other integer or fully-masked IntMask is contained in this IntMask. Example: 0x1 in IntMask("0xf1/0xff"): True 0x1 in IntMask("0xf1/0x0f"): True 0x1 in IntMask("0xf1/0xf0"): False """ if isinstance(other, IntMask): if other.fully(): return other.value in self else: raise ValueError( "Comparing non fully-masked IntMasks is not supported" ) else: return other & self._mask == self._value & self._mask def dict(self): return {"value": self._value, "mask": self._mask} def to_json(self): return self.dict() class Mask8(IntMask): size = 8 class Mask16(IntMask): size = 16 class Mask32(IntMask): size = 32 class Mask64(IntMask): size = 64 class Mask128(IntMask): size = 128 class Mask992(IntMask): size = 992 def decode_mask(mask_size): """Value/Mask decoder for values of specific size (bits). Used for fields such as: reg0=0x248/0xff """ class Mask(IntMask): size = mask_size __name__ = "Mask{}".format(size) return Mask class EthMask(Decoder): """EthMask represents an Ethernet address with optional mask. It uses netaddr.EUI. Attributes: eth (netaddr.EUI): The Ethernet address. mask (netaddr.EUI): Optional, the Ethernet address mask. Args: string (str): A string representing the masked Ethernet address e.g: 00.11:22:33:44:55 or 01:00:22:00:33:00/01:00:00:00:00:00 """ def __init__(self, string): mask_parts = string.split("/") self._eth = netaddr.EUI(mask_parts[0]) if len(mask_parts) == 2: self._mask = netaddr.EUI(mask_parts[1]) else: self._mask = None @property def eth(self): """The Ethernet address.""" return self._eth @property def mask(self): """The Ethernet address mask.""" return self._mask def __eq__(self, other): """Equality operator. Both the Ethernet address and the mask are compared. This can be used to implement filters where we expect a specific mask to be present, e.g: dl_dst=01:00:00:00:00:00/01:00:00:00:00:00. Args: other (EthMask): Another EthMask to compare against. Returns: True if this EthMask is the same as the other. """ return self._mask == other._mask and self._eth == other._eth def __contains__(self, other): """Contains operator. Args: other (netaddr.EUI or EthMask): An Ethernet address. Returns: True if the other netaddr.EUI or fully-masked EthMask is contained in this EthMask's address range. """ if isinstance(other, EthMask): if other._mask: raise ValueError( "Comparing non fully-masked EthMask is not supported" ) return other._eth in self if self._mask: return (other.value & self._mask.value) == ( self._eth.value & self._mask.value ) else: return other == self._eth def __str__(self): if self._mask: return "/".join( [ self._eth.format(netaddr.mac_unix), self._mask.format(netaddr.mac_unix), ] ) else: return self._eth.format(netaddr.mac_unix) def __repr__(self): return "%s('%s')" % (self.__class__.__name__, self) def to_json(self): return str(self) class IPMask(Decoder): """IPMask stores an IPv6 or IPv4 and a mask. It uses netaddr.IPAddress. IPMasks can represent valid CIDRs or randomly masked IP Addresses. Args: string (str): A string representing the ip/mask. """ def __init__(self, string): self._ipnet = None self._ip = None self._mask = None try: self._ipnet = netaddr.IPNetwork(string) except netaddr.AddrFormatError: pass if not self._ipnet: # It's not a valid CIDR. Store ip and mask independently. parts = string.split("/") if len(parts) != 2: raise ValueError( "value {}: is not an ipv4 or ipv6 address".format(string) ) try: self._ip = netaddr.IPAddress(parts[0]) self._mask = netaddr.IPAddress(parts[1]) except netaddr.AddrFormatError as exc: raise ValueError( "value {}: is not an ipv4 or ipv6 address".format(string) ) from exc def __eq__(self, other): """Equality operator. Both the IPAddress and the mask are compared. This can be used to implement filters where a specific mask is expected, e.g: nw_src=192.168.1.0/24. Args: other (IPMask or netaddr.IPNetwork or netaddr.IPAddress): Another IPAddress or IPNetwork to compare against. Returns: True if this IPMask is the same as the other. """ if isinstance(other, netaddr.IPNetwork): return self._ipnet and self._ipnet == other if isinstance(other, netaddr.IPAddress): return self._ipnet and self._ipnet.ip == other elif isinstance(other, IPMask): if self._ipnet: return self._ipnet == other._ipnet return self._ip == other._ip and self._mask == other._mask else: return False def __contains__(self, other): """Contains operator. Only comparing valid CIDRs is supported. Args: other (netaddr.IPAddress or IPMask): An IP address. Returns: True if the other IPAddress is contained in this IPMask's address range. """ if isinstance(other, IPMask): if not other._ipnet: raise ValueError("Only comparing valid CIDRs is supported") return ( netaddr.IPAddress(other._ipnet.first) in self and netaddr.IPAddress(other._ipnet.last) in self ) elif isinstance(other, netaddr.IPAddress): if self._ipnet: return other in self._ipnet return (other & self._mask) == (self._ip & self._mask) def cidr(self): """ Returns True if the IPMask is a valid CIDR. """ return self._ipnet is not None @property def ip(self): """The IP address.""" if self._ipnet: return self._ipnet.ip return self._ip @property def mask(self): """The IP mask.""" if self._ipnet: return self._ipnet.netmask return self._mask def __str__(self): if self._ipnet: return str(self._ipnet) return "/".join([str(self._ip), str(self._mask)]) def __repr__(self): return "%s('%s')" % (self.__class__.__name__, self) def to_json(self): return str(self) def decode_free_output(value): """The value of the output action can be found free, i.e: without the 'output' keyword. This decoder decodes its value when found this way.""" try: return "output", {"port": int(value)} except ValueError: return "output", {"port": value.strip('"')} ipv4 = r"(?:\d{1,3}.?){3}\d{1,3}" ipv4_capture = r"({ipv4})".format(ipv4=ipv4) ipv6 = r"[\w:\.]+" ipv6_capture = r"(?:\[)?({ipv6})(?:\])?".format(ipv6=ipv6) port_range = r":(\d+)(?:-(\d+))?" ip_range_regexp = r"{ip_cap}(?:-{ip_cap})?(?:{port_range})?" ipv4_port_regex = re.compile( ip_range_regexp.format(ip_cap=ipv4_capture, port_range=port_range) ) ipv6_port_regex = re.compile( ip_range_regexp.format(ip_cap=ipv6_capture, port_range=port_range) ) def decode_ip_port_range(value): """ Decodes an IP and port range: {ip_start}-{ip-end}:{port_start}-{port_end} IPv6 addresses are surrounded by "[" and "]" if port ranges are also present Returns the following dictionary: { "addrs": { "start": {ip_start} "end": {ip_end} } "ports": { "start": {port_start}, "end": {port_end} } (the "ports" key might be omitted) """ if value.count(":") > 1: match = ipv6_port_regex.match(value) else: match = ipv4_port_regex.match(value) ip_start = match.group(1) ip_end = match.group(2) port_start = match.group(3) port_end = match.group(4) result = { "addrs": { "start": netaddr.IPAddress(ip_start), "end": netaddr.IPAddress(ip_end or ip_start), } } if port_start: result["ports"] = { "start": int(port_start), "end": int(port_end or port_start), } return result def decode_nat(value): """Decodes the 'nat' keyword of the ct action. The format is: nat Flag format. nat(type=addrs[:ports][,flag]...) Full format where the address-port range has the same format as the one described in decode_ip_port_range. Examples: nat(src=0.0.0.0) nat(src=0.0.0.0,persistent) nat(dst=192.168.1.0-192.168.1.253:4000-5000) nat(dst=192.168.1.0-192.168.1.253,hash) nat(dst=[fe80::f150]-[fe80::f15f]:255-300) """ if not value: return True # If flag format, the value is True. result = dict() type_parts = value.split("=") result["type"] = type_parts[0] if len(type_parts) > 1: value_parts = type_parts[1].split(",") if len(type_parts) != 2: raise ValueError("Malformed nat action: %s" % value) ip_port_range = decode_ip_port_range(value_parts[0]) result = {"type": type_parts[0], **ip_port_range} for flag in value_parts[1:]: result[flag] = True return result class FlowEncoder(json.JSONEncoder): """FlowEncoder is a json.JSONEncoder instance that can be used to serialize flow fields.""" def default(self, obj): if isinstance(obj, Decoder): return obj.to_json() elif isinstance(obj, netaddr.IPAddress): return str(obj) return json.JSONEncoder.default(self, obj)

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