Stem Docs

stem.exit_policy

Source code for stem.exit_policy

# Copyright 2012-2013, Damian Johnson
# Copyright 2013, Sean Robinson
# See LICENSE for licensing information

"""
Representation of tor exit policies. These can be easily used to check if
exiting to a destination is permissible or not. For instance...

::

  >>> from stem.exit_policy import ExitPolicy, MicroExitPolicy
  >>> policy = ExitPolicy("accept *:80", "accept *:443", "reject *:*")
  >>> print policy
  accept *:80, accept *:443, reject *:*
  >>> print policy.summary()
  accept 80, 443
  >>> policy.can_exit_to("75.119.206.243", 80)
  True

  >>> policy = MicroExitPolicy("accept 80,443")
  >>> print policy
  accept 80,443
  >>> policy.can_exit_to("75.119.206.243", 80)
  True

::

  ExitPolicy - Exit policy for a Tor relay
    |  + MicroExitPolicy - Microdescriptor exit policy
    |- can_exit_to - check if exiting to this destination is allowed or not
    |- is_exiting_allowed - check if any exiting is allowed
    |- summary - provides a short label, similar to a microdescriptor
    |- __str__  - string representation
    +- __iter__ - ExitPolicyRule entries that this contains

  ExitPolicyRule - Single rule of an exit policy chain
    |- is_address_wildcard - checks if we'll accept any address
    |- is_port_wildcard - checks if we'll accept any port
    |- get_address_type - provides the protocol our ip address belongs to
    |- is_match - checks if we match a given destination
    |- get_mask - provides the address representation of our mask
    |- get_masked_bits - provides the bit representation of our mask
    +- __str__ - string representation for this rule

  get_config_policy - provides the ExitPolicy based on torrc rules

.. data:: AddressType (enum)

  Enumerations for IP address types that can be in an exit policy.

  ============ ===========
  AddressType  Description
  ============ ===========
  **WILDCARD** any address of either IPv4 or IPv6
  **IPv4**     IPv4 address
  **IPv6**     IPv6 address
  ============ ===========
"""

import stem.util.connection
import stem.util.enum

AddressType = stem.util.enum.Enum(("WILDCARD", "Wildcard"), ("IPv4", "IPv4"), ("IPv6", "IPv6"))

# Addresses aliased by the 'private' policy. From the tor man page...
#
# To specify all internal and link-local networks (including 0.0.0.0/8,
# 169.254.0.0/16, 127.0.0.0/8, 192.168.0.0/16, 10.0.0.0/8, and 172.16.0.0/12),
# you can use the "private" alias instead of an address.

PRIVATE_ADDRESSES = (
  "0.0.0.0/8",
  "169.254.0.0/16",
  "127.0.0.0/8",
  "192.168.0.0/16",
  "10.0.0.0/8",
  "172.16.0.0/12",
)


# TODO: The ExitPolicyRule could easily be a mutable class if we did the
# following...
#
# * Provided setter methods that acquired an RLock which also wrapped all of
#   our current methods to provide thread safety.
#
# * Reset our derived attributes (self._addr_bin, self._mask_bin, and
#   self._str_representation) when we changed something that it was based on.
#
# That said, I'm not sure if this is entirely desirable since for most use
# cases we *want* the caller to have an immutable ExitPolicy (since it
# reflects something they... well, can't modify). However, I can think of
# some use cases where we might want to construct custom policies. Maybe make
# it a CustomExitPolicyRule subclass?

[docs]def get_config_policy(rules): """ Converts an ExitPolicy found in a torrc to a proper exit pattern. This accounts for... * ports being optional * the 'private' keyword :param str,list rules: comma separated rules or list to be converted :returns: :class:`~stem.exit_policy.ExitPolicy` reflected by the rules :raises: **ValueError** if input isn't a valid tor exit policy """ if isinstance(rules, (str, unicode)): rules = rules.split(',') result = [] for rule in rules: rule = rule.strip() if not rule: continue if not ':' in rule: rule = "%s:*" % rule if 'private' in rule: acceptance = rule.split(' ', 1)[0] port = rule.split(':', 1)[1] for private_addr in PRIVATE_ADDRESSES: result.append(ExitPolicyRule("%s %s:%s" % (acceptance, private_addr, port))) else: result.append(ExitPolicyRule(rule)) return ExitPolicy(*result)
[docs]class ExitPolicy(object): """ Policy for the destinations that a relay allows or denies exiting to. This is, in effect, just a list of :class:`~stem.exit_policy.ExitPolicyRule` entries. :param list rules: **str** or :class:`~stem.exit_policy.ExitPolicyRule` entries that make up this policy """ def __init__(self, *rules): # sanity check the types for rule in rules: if not isinstance(rule, (str, unicode, ExitPolicyRule)): raise TypeError("Exit policy rules can only contain strings or ExitPolicyRules, got a %s (%s)" % (type(rule), rules)) self._rules = None # lazily loaded series of ExitPolicyRule self._input_rules = rules # input rules, only kept until self._rules is set self._is_allowed_default = True self._summary_representation = None self._can_exit_to_cache = {}
[docs] def can_exit_to(self, address = None, port = None): """ Checks if this policy allows exiting to a given destination or not. If the address or port is omitted then this will check if we allow for its wildcard. :param str address: IPv4 or IPv6 address (with or without brackets) :param int port: port number :returns: **True** if exiting to this destination is allowed, **False** otherwise """ if not (address, port) in self._can_exit_to_cache: result = self._is_allowed_default for rule in self._get_rules(): if rule.is_match(address, port): result = rule.is_accept break self._can_exit_to_cache[(address, port)] = result return self._can_exit_to_cache[(address, port)]
[docs] def is_exiting_allowed(self): """ Provides **True** if the policy allows exiting whatsoever, **False** otherwise. """ rejected_ports = set() for rule in self._get_rules(): if rule.is_accept: for port in xrange(rule.min_port, rule.max_port + 1): if not port in rejected_ports: return True elif rule.is_address_wildcard(): if rule.is_port_wildcard(): return False else: rejected_ports.update(range(rule.min_port, rule.max_port + 1)) return self._is_allowed_default
[docs] def summary(self): """ Provides a short description of our policy chain, similar to a microdescriptor. This excludes entries that don't cover all IP addresses, and is either white-list or blacklist policy based on the final entry. For instance... :: >>> policy = ExitPolicy('accept *:80', 'accept *:443', 'reject *:*') >>> policy.summary() "accept 80, 443" >>> policy = ExitPolicy('accept *:443', 'reject *:1-1024', 'accept *:*') >>> policy.summary() "reject 1-442, 444-1024" :returns: **str** with a concise summary for our policy """ if self._summary_representation is None: # determines if we're a white-list or blacklist is_whitelist = not self._is_allowed_default for rule in self._get_rules(): if rule.is_address_wildcard() and rule.is_port_wildcard(): is_whitelist = not rule.is_accept break # Iterates over the policies and adds the the ports we'll return (ie, # allows if a white-list and rejects if a blacklist). Regardless of a # port's allow/reject policy, all further entries with that port are # ignored since policies respect the first matching policy. display_ports, skip_ports = [], set() for rule in self._get_rules(): if not rule.is_address_wildcard(): continue elif rule.is_port_wildcard(): break for port in xrange(rule.min_port, rule.max_port + 1): if port in skip_ports: continue # if accept + white-list or reject + blacklist then add if rule.is_accept == is_whitelist: display_ports.append(port) # all further entries with this port should be ignored skip_ports.add(port) # convert port list to a list of ranges (ie, ['1-3'] rather than [1, 2, 3]) if display_ports: display_ranges, temp_range = [], [] display_ports.sort() display_ports.append(None) # ending item to include last range in loop for port in display_ports: if not temp_range or temp_range[-1] + 1 == port: temp_range.append(port) else: if len(temp_range) > 1: display_ranges.append("%i-%i" % (temp_range[0], temp_range[-1])) else: display_ranges.append(str(temp_range[0])) temp_range = [port] else: # everything for the inverse is_whitelist = not is_whitelist display_ranges = ["1-65535"] # constructs the summary string label_prefix = "accept " if is_whitelist else "reject " self._summary_representation = (label_prefix + ", ".join(display_ranges)).strip() return self._summary_representation
def _set_default_allowed(self, is_allowed_default): """ Generally policies end with either an 'reject \*:\*' or 'accept \*:\*' policy, but if it doesn't then is_allowed_default will determine the default response for our :meth:`~stem.exit_policy.ExitPolicy.can_exit_to` method. Our default, and tor's, is **True**. :param bool is_allowed_default: :meth:`~stem.exit_policy.ExitPolicy.can_exit_to` default when no rules apply """ self._is_allowed_default = is_allowed_default self._can_exit_to_cache = {} def _get_rules(self): if self._rules is None: rules = [] is_all_accept, is_all_reject = True, True for rule in self._input_rules: if isinstance(rule, (str, unicode)): rule = ExitPolicyRule(rule.strip()) if rule.is_accept: is_all_reject = False else: is_all_accept = False rules.append(rule) if rule.is_address_wildcard() and rule.is_port_wildcard(): break # this is a catch-all, no reason to include more # If we only have one kind of entry *and* end with a wildcard then # we might as well use the simpler version. For instance... # # reject *:80, reject *:443, reject *:* # # ... could also be represented as simply... # # reject *:* # # This mostly comes up with reject-all policies because the # 'reject private:*' appends an extra seven rules that have no # effect. if rules and (rules[-1].is_address_wildcard() and rules[-1].is_port_wildcard()): if is_all_accept: rules = [ExitPolicyRule("accept *:*")] elif is_all_reject: rules = [ExitPolicyRule("reject *:*")] self._rules = rules self._input_rules = None return self._rules def __iter__(self): for rule in self._get_rules(): yield rule def __str__(self): return ', '.join([str(rule) for rule in self._get_rules()]) def __eq__(self, other): if isinstance(other, ExitPolicy): return self._get_rules() == list(other) else: return False
[docs]class MicroExitPolicy(ExitPolicy): """ Exit policy provided by the microdescriptors. This is a distilled version of a normal :class:`~stem.exit_policy.ExitPolicy` contains, just consisting of a list of ports that are either accepted or rejected. For instance... :: accept 80,443 # only accepts common http ports reject 1-1024 # only accepts non-privileged ports Since these policies are a subset of the exit policy information (lacking IP ranges) clients can only use them to guess if a relay will accept traffic or not. To quote the `dir-spec <https://gitweb.torproject.org/torspec.git/blob/HEAD:/dir-spec.txt>`_ (section 3.2.1)... :: With microdescriptors, clients don't learn exact exit policies: clients can only guess whether a relay accepts their request, try the BEGIN request, and might get end-reason-exit-policy if they guessed wrong, in which case they'll have to try elsewhere. :var bool is_accept: **True** if these are ports that we accept, **False** if they're ports that we reject :param str policy: policy string that describes this policy """ def __init__(self, policy): # Microdescriptor policies are of the form... # # MicrodescriptrPolicy ::= ("accept" / "reject") SP PortList NL # PortList ::= PortOrRange # PortList ::= PortList "," PortOrRange # PortOrRange ::= INT "-" INT / INT self._policy = policy if policy.startswith("accept"): self.is_accept = True elif policy.startswith("reject"): self.is_accept = False else: raise ValueError("A microdescriptor exit policy must start with either 'accept' or 'reject': %s" % policy) policy = policy[6:] if not policy.startswith(" ") or (len(policy) - 1 != len(policy.lstrip())): raise ValueError("A microdescriptor exit policy should have a space separating accept/reject from its port list: %s" % self._policy) policy = policy[1:] # convert our port list into MicroExitPolicyRule rules = [] for port_entry in policy.split(","): if '-' in port_entry: min_port, max_port = port_entry.split('-', 1) else: min_port = max_port = port_entry if not stem.util.connection.is_valid_port(min_port) or \ not stem.util.connection.is_valid_port(max_port): raise ValueError("'%s' is an invalid port range" % port_entry) rules.append(MicroExitPolicyRule(self.is_accept, int(min_port), int(max_port))) super(MicroExitPolicy, self).__init__(*rules) self._set_default_allowed(not self.is_accept) def __str__(self): return self._policy def __eq__(self, other): if isinstance(other, MicroExitPolicy): return str(self) == str(other) else: return False
[docs]class ExitPolicyRule(object): """ Single rule from the user's exit policy. These rules are chained together to form complete policies that describe where a relay will and will not allow traffic to exit. The format of these rules are formally described in the `dir-spec <https://gitweb.torproject.org/torspec.git/blob/HEAD:/dir-spec.txt>`_ as an "exitpattern". Note that while these are similar to tor's man page entry for ExitPolicies, it's not the exact same. An exitpattern is better defined and stricter in what it'll accept. For instance, ports are not optional and it does not contain the 'private' alias. This should be treated as an immutable object. :var bool is_accept: indicates if exiting is allowed or disallowed :var str address: address that this rule is for :var int min_port: lower end of the port range that we include (inclusive) :var int max_port: upper end of the port range that we include (inclusive) :param str rule: exit policy rule to be parsed :raises: **ValueError** if input isn't a valid tor exit policy rule """ def __init__(self, rule): # policy ::= "accept" exitpattern | "reject" exitpattern # exitpattern ::= addrspec ":" portspec if rule.startswith("accept"): self.is_accept = True elif rule.startswith("reject"): self.is_accept = False else: raise ValueError("An exit policy must start with either 'accept' or 'reject': %s" % rule) exitpattern = rule[6:] if not exitpattern.startswith(" ") or (len(exitpattern) - 1 != len(exitpattern.lstrip())): raise ValueError("An exit policy should have a space separating its accept/reject from the exit pattern: %s" % rule) exitpattern = exitpattern[1:] if not ":" in exitpattern: raise ValueError("An exitpattern must be of the form 'addrspec:portspec': %s" % rule) self.address = None self._address_type = None self._masked_bits = None self.min_port = self.max_port = None # Our mask in ip notation (ex. "255.255.255.0"). This is only set if we # either have a custom mask that can't be represented by a number of bits, # or the user has called mask(), lazily loading this. self._mask = None addrspec, portspec = exitpattern.rsplit(":", 1) self._apply_addrspec(rule, addrspec) self._apply_portspec(rule, portspec) # The integer representation of our mask and masked address. These are # lazily loaded and used by our is_match() method to compare ourselves to # other addresses. self._mask_bin = self._addr_bin = None # Lazily loaded string representation of our policy. self._str_representation = None
[docs] def is_address_wildcard(self): """ **True** if we'll match against any address, **False** otherwise. Note that this may be different from matching against a /0 because policies can contain both IPv4 and IPv6 addresses (so 0.0.0.0/0 won't match against an IPv6 address). :returns: **bool** for if our address matching is a wildcard """ return self._address_type == _address_type_to_int(AddressType.WILDCARD)
[docs] def is_port_wildcard(self): """ **True** if we'll match against any port, **False** otherwise. :returns: **bool** for if our port matching is a wildcard """ return self.min_port in (0, 1) and self.max_port == 65535
[docs] def is_match(self, address = None, port = None): """ **True** if we match against the given destination, **False** otherwise. If the address or port is omitted then that'll only match against a wildcard. :param str address: IPv4 or IPv6 address (with or without brackets) :param int port: port number :returns: **bool** indicating if we match against this destination :raises: **ValueError** if provided with a malformed address or port """ # validate our input and check if the argument doesn't match our address type if address is not None: address_type = self.get_address_type() if stem.util.connection.is_valid_ipv4_address(address): if address_type == AddressType.IPv6: return False elif stem.util.connection.is_valid_ipv6_address(address, allow_brackets = True): if address_type == AddressType.IPv4: return False address = address.lstrip("[").rstrip("]") else: raise ValueError("'%s' isn't a valid IPv4 or IPv6 address" % address) if port is not None and not stem.util.connection.is_valid_port(port): raise ValueError("'%s' isn't a valid port" % port) if not self.is_address_wildcard(): # Already got the integer representation of our mask and our address # with the mask applied. Just need to check if this address with the # mask applied matches. if address is None: return False else: comparison_addr_bin = int(stem.util.connection._get_address_binary(address), 2) comparison_addr_bin &= self._get_mask_bin() if self._get_address_bin() != comparison_addr_bin: return False if not self.is_port_wildcard(): if port is None: return False elif port < self.min_port or port > self.max_port: return False return True
[docs] def get_address_type(self): """ Provides the :data:`~stem.exit_policy.AddressType` for our policy. :returns: :data:`~stem.exit_policy.AddressType` for the type of address that we have """ return _int_to_address_type(self._address_type)
[docs] def get_mask(self, cache = True): """ Provides the address represented by our mask. This is **None** if our address type is a wildcard. :param bool cache: caches the result if **True** :returns: str of our subnet mask for the address (ex. "255.255.255.0") """ # Lazy loading our mask because it very infrequently requested. There's # no reason to usually usse memory for it. if not self._mask: address_type = self.get_address_type() if address_type == AddressType.WILDCARD: mask = None elif address_type == AddressType.IPv4: mask = stem.util.connection.get_mask_ipv4(self._masked_bits) elif address_type == AddressType.IPv6: mask = stem.util.connection.get_mask_ipv6(self._masked_bits) if not cache: return mask self._mask = mask return self._mask
[docs] def get_masked_bits(self): """ Provides the number of bits our subnet mask represents. This is **None** if our mask can't have a bit representation. :returns: int with the bit representation of our mask """ return self._masked_bits
def __str__(self): """ Provides the string representation of our policy. This does not necessarily match the rule that we were constructed from (due to things like IPv6 address collapsing or the multiple representations that our mask can have). However, it is a valid that would be accepted by our constructor to re-create this rule. """ if self._str_representation is None: label = "accept " if self.is_accept else "reject " if self.is_address_wildcard(): label += "*:" else: address_type = self.get_address_type() if address_type == AddressType.IPv4: label += self.address else: label += "[%s]" % self.address # Including our mask label as follows... # - exclude our mask if it doesn't do anything # - use our masked bit count if we can # - use the mask itself otherwise if (address_type == AddressType.IPv4 and self._masked_bits == 32) or \ (address_type == AddressType.IPv6 and self._masked_bits == 128): label += ":" elif self._masked_bits is not None: label += "/%i:" % self._masked_bits else: label += "/%s:" % self.get_mask() if self.is_port_wildcard(): label += "*" elif self.min_port == self.max_port: label += str(self.min_port) else: label += "%i-%i" % (self.min_port, self.max_port) self._str_representation = label return self._str_representation def _get_mask_bin(self): # provides an integer representation of our mask if self._mask_bin is None: self._mask_bin = int(stem.util.connection._get_address_binary(self.get_mask(False)), 2) return self._mask_bin def _get_address_bin(self): # provides an integer representation of our address if self._addr_bin is None: self._addr_bin = int(stem.util.connection._get_address_binary(self.address), 2) & self._mask_bin return self._addr_bin def _apply_addrspec(self, rule, addrspec): # Parses the addrspec... # addrspec ::= "*" | ip4spec | ip6spec if "/" in addrspec: self.address, addr_extra = addrspec.split("/", 1) else: self.address, addr_extra = addrspec, None if addrspec == "*": self._address_type = _address_type_to_int(AddressType.WILDCARD) self.address = self._masked_bits = None elif stem.util.connection.is_valid_ipv4_address(self.address): # ipv4spec ::= ip4 | ip4 "/" num_ip4_bits | ip4 "/" ip4mask # ip4 ::= an IPv4 address in dotted-quad format # ip4mask ::= an IPv4 mask in dotted-quad format # num_ip4_bits ::= an integer between 0 and 32 self._address_type = _address_type_to_int(AddressType.IPv4) if addr_extra is None: self._masked_bits = 32 elif stem.util.connection.is_valid_ipv4_address(addr_extra): # provided with an ip4mask try: self._masked_bits = stem.util.connection._get_masked_bits(addr_extra) except ValueError: # mask can't be represented as a number of bits (ex. "255.255.0.255") self._mask = addr_extra self._masked_bits = None elif addr_extra.isdigit(): # provided with a num_ip4_bits self._masked_bits = int(addr_extra) if self._masked_bits < 0 or self._masked_bits > 32: raise ValueError("IPv4 masks must be in the range of 0-32 bits") else: raise ValueError("The '%s' isn't a mask nor number of bits: %s" % (addr_extra, rule)) elif self.address.startswith("[") and self.address.endswith("]") and \ stem.util.connection.is_valid_ipv6_address(self.address[1:-1]): # ip6spec ::= ip6 | ip6 "/" num_ip6_bits # ip6 ::= an IPv6 address, surrounded by square brackets. # num_ip6_bits ::= an integer between 0 and 128 self.address = stem.util.connection.expand_ipv6_address(self.address[1:-1].upper()) self._address_type = _address_type_to_int(AddressType.IPv6) if addr_extra is None: self._masked_bits = 128 elif addr_extra.isdigit(): # provided with a num_ip6_bits self._masked_bits = int(addr_extra) if self._masked_bits < 0 or self._masked_bits > 128: raise ValueError("IPv6 masks must be in the range of 0-128 bits") else: raise ValueError("The '%s' isn't a number of bits: %s" % (addr_extra, rule)) else: raise ValueError("Address isn't a wildcard, IPv4, or IPv6 address: %s" % rule) def _apply_portspec(self, rule, portspec): # Parses the portspec... # portspec ::= "*" | port | port "-" port # port ::= an integer between 1 and 65535, inclusive. # # Due to a tor bug the spec says that we should accept port of zero, but # connections to port zero are never permitted. if portspec == "*": self.min_port, self.max_port = 1, 65535 elif portspec.isdigit(): # provided with a single port if stem.util.connection.is_valid_port(portspec, allow_zero = True): self.min_port = self.max_port = int(portspec) else: raise ValueError("'%s' isn't within a valid port range: %s" % (portspec, rule)) elif "-" in portspec: # provided with a port range port_comp = portspec.split("-", 1) if stem.util.connection.is_valid_port(port_comp, allow_zero = True): self.min_port = int(port_comp[0]) self.max_port = int(port_comp[1]) if self.min_port > self.max_port: raise ValueError("Port range has a lower bound that's greater than its upper bound: %s" % rule) else: raise ValueError("Malformed port range: %s" % rule) else: raise ValueError("Port value isn't a wildcard, integer, or range: %s" % rule) def __eq__(self, other): if isinstance(other, ExitPolicyRule): # Our string representation encompasses our effective policy. Technically # this isn't quite right since our rule attribute may differ (ie, "accept # 0.0.0.0/0" == "accept 0.0.0.0/0.0.0.0" will be True), but these # policies are effectively equivalent. return str(self) == str(other) else: return False
def _address_type_to_int(address_type): return AddressType.index_of(address_type) def _int_to_address_type(address_type_int): return AddressType[AddressType.keys()[address_type_int]]
[docs]class MicroExitPolicyRule(ExitPolicyRule): """ Lighter weight ExitPolicyRule derivative for microdescriptors. """ def __init__(self, is_accept, min_port, max_port): self.is_accept = is_accept self.address = None # wildcard address self.min_port = min_port self.max_port = max_port self._str_representation = None
[docs] def is_address_wildcard(self): return True
[docs] def get_address_type(self): return AddressType.WILDCARD
[docs] def get_mask(self, cache = True): return None
[docs] def get_masked_bits(self): return None