--- /dev/null
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright (c) 2012 OpenStack, LLC.
+# All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+"""
+Common Policy Engine Implementation
+
+Policies can be expressed in one of two forms: A list of lists, or a
+string written in the new policy language.
+
+In the list-of-lists representation, each check inside the innermost
+list is combined as with an "and" conjunction--for that check to pass,
+all the specified checks must pass. These innermost lists are then
+combined as with an "or" conjunction. This is the original way of
+expressing policies, but there now exists a new way: the policy
+language.
+
+In the policy language, each check is specified the same way as in the
+list-of-lists representation: a simple "a:b" pair that is matched to
+the correct code to perform that check. However, conjunction
+operators are available, allowing for more expressiveness in crafting
+policies.
+
+As an example, take the following rule, expressed in the list-of-lists
+representation::
+
+ [["role:admin"], ["project_id:%(project_id)s", "role:projectadmin"]]
+
+In the policy language, this becomes::
+
+ role:admin or (project_id:%(project_id)s and role:projectadmin)
+
+The policy language also has the "not" operator, allowing a richer
+policy rule::
+
+ project_id:%(project_id)s and not role:dunce
+
+Finally, two special policy checks should be mentioned; the policy
+check "@" will always accept an access, and the policy check "!" will
+always reject an access. (Note that if a rule is either the empty
+list ("[]") or the empty string, this is equivalent to the "@" policy
+check.) Of these, the "!" policy check is probably the most useful,
+as it allows particular rules to be explicitly disabled.
+"""
+
+import abc
+import logging
+import re
+import urllib
+
+import urllib2
+
+from heat.openstack.common.gettextutils import _
+from heat.openstack.common import jsonutils
+
+
+LOG = logging.getLogger(__name__)
+
+
+_rules = None
+_checks = {}
+
+
+class Rules(dict):
+ """
+ A store for rules. Handles the default_rule setting directly.
+ """
+
+ @classmethod
+ def load_json(cls, data, default_rule=None):
+ """
+ Allow loading of JSON rule data.
+ """
+
+ # Suck in the JSON data and parse the rules
+ rules = dict((k, parse_rule(v)) for k, v in
+ jsonutils.loads(data).items())
+
+ return cls(rules, default_rule)
+
+ def __init__(self, rules=None, default_rule=None):
+ """Initialize the Rules store."""
+
+ super(Rules, self).__init__(rules or {})
+ self.default_rule = default_rule
+
+ def __missing__(self, key):
+ """Implements the default rule handling."""
+
+ # If the default rule isn't actually defined, do something
+ # reasonably intelligent
+ if not self.default_rule or self.default_rule not in self:
+ raise KeyError(key)
+
+ return self[self.default_rule]
+
+ def __str__(self):
+ """Dumps a string representation of the rules."""
+
+ # Start by building the canonical strings for the rules
+ out_rules = {}
+ for key, value in self.items():
+ # Use empty string for singleton TrueCheck instances
+ if isinstance(value, TrueCheck):
+ out_rules[key] = ''
+ else:
+ out_rules[key] = str(value)
+
+ # Dump a pretty-printed JSON representation
+ return jsonutils.dumps(out_rules, indent=4)
+
+
+# Really have to figure out a way to deprecate this
+def set_rules(rules):
+ """Set the rules in use for policy checks."""
+
+ global _rules
+
+ _rules = rules
+
+
+# Ditto
+def reset():
+ """Clear the rules used for policy checks."""
+
+ global _rules
+
+ _rules = None
+
+
+def check(rule, target, creds, exc=None, *args, **kwargs):
+ """
+ Checks authorization of a rule against the target and credentials.
+
+ :param rule: The rule to evaluate.
+ :param target: As much information about the object being operated
+ on as possible, as a dictionary.
+ :param creds: As much information about the user performing the
+ action as possible, as a dictionary.
+ :param exc: Class of the exception to raise if the check fails.
+ Any remaining arguments passed to check() (both
+ positional and keyword arguments) will be passed to
+ the exception class. If exc is not provided, returns
+ False.
+
+ :return: Returns False if the policy does not allow the action and
+ exc is not provided; otherwise, returns a value that
+ evaluates to True. Note: for rules using the "case"
+ expression, this True value will be the specified string
+ from the expression.
+ """
+
+ # Allow the rule to be a Check tree
+ if isinstance(rule, BaseCheck):
+ result = rule(target, creds)
+ elif not _rules:
+ # No rules to reference means we're going to fail closed
+ result = False
+ else:
+ try:
+ # Evaluate the rule
+ result = _rules[rule](target, creds)
+ except KeyError:
+ # If the rule doesn't exist, fail closed
+ result = False
+
+ # If it is False, raise the exception if requested
+ if exc and result is False:
+ raise exc(*args, **kwargs)
+
+ return result
+
+
+class BaseCheck(object):
+ """
+ Abstract base class for Check classes.
+ """
+
+ __metaclass__ = abc.ABCMeta
+
+ @abc.abstractmethod
+ def __str__(self):
+ """
+ Retrieve a string representation of the Check tree rooted at
+ this node.
+ """
+
+ pass
+
+ @abc.abstractmethod
+ def __call__(self, target, cred):
+ """
+ Perform the check. Returns False to reject the access or a
+ true value (not necessary True) to accept the access.
+ """
+
+ pass
+
+
+class FalseCheck(BaseCheck):
+ """
+ A policy check that always returns False (disallow).
+ """
+
+ def __str__(self):
+ """Return a string representation of this check."""
+
+ return "!"
+
+ def __call__(self, target, cred):
+ """Check the policy."""
+
+ return False
+
+
+class TrueCheck(BaseCheck):
+ """
+ A policy check that always returns True (allow).
+ """
+
+ def __str__(self):
+ """Return a string representation of this check."""
+
+ return "@"
+
+ def __call__(self, target, cred):
+ """Check the policy."""
+
+ return True
+
+
+class Check(BaseCheck):
+ """
+ A base class to allow for user-defined policy checks.
+ """
+
+ def __init__(self, kind, match):
+ """
+ :param kind: The kind of the check, i.e., the field before the
+ ':'.
+ :param match: The match of the check, i.e., the field after
+ the ':'.
+ """
+
+ self.kind = kind
+ self.match = match
+
+ def __str__(self):
+ """Return a string representation of this check."""
+
+ return "%s:%s" % (self.kind, self.match)
+
+
+class NotCheck(BaseCheck):
+ """
+ A policy check that inverts the result of another policy check.
+ Implements the "not" operator.
+ """
+
+ def __init__(self, rule):
+ """
+ Initialize the 'not' check.
+
+ :param rule: The rule to negate. Must be a Check.
+ """
+
+ self.rule = rule
+
+ def __str__(self):
+ """Return a string representation of this check."""
+
+ return "not %s" % self.rule
+
+ def __call__(self, target, cred):
+ """
+ Check the policy. Returns the logical inverse of the wrapped
+ check.
+ """
+
+ return not self.rule(target, cred)
+
+
+class AndCheck(BaseCheck):
+ """
+ A policy check that requires that a list of other checks all
+ return True. Implements the "and" operator.
+ """
+
+ def __init__(self, rules):
+ """
+ Initialize the 'and' check.
+
+ :param rules: A list of rules that will be tested.
+ """
+
+ self.rules = rules
+
+ def __str__(self):
+ """Return a string representation of this check."""
+
+ return "(%s)" % ' and '.join(str(r) for r in self.rules)
+
+ def __call__(self, target, cred):
+ """
+ Check the policy. Requires that all rules accept in order to
+ return True.
+ """
+
+ for rule in self.rules:
+ if not rule(target, cred):
+ return False
+
+ return True
+
+ def add_check(self, rule):
+ """
+ Allows addition of another rule to the list of rules that will
+ be tested. Returns the AndCheck object for convenience.
+ """
+
+ self.rules.append(rule)
+ return self
+
+
+class OrCheck(BaseCheck):
+ """
+ A policy check that requires that at least one of a list of other
+ checks returns True. Implements the "or" operator.
+ """
+
+ def __init__(self, rules):
+ """
+ Initialize the 'or' check.
+
+ :param rules: A list of rules that will be tested.
+ """
+
+ self.rules = rules
+
+ def __str__(self):
+ """Return a string representation of this check."""
+
+ return "(%s)" % ' or '.join(str(r) for r in self.rules)
+
+ def __call__(self, target, cred):
+ """
+ Check the policy. Requires that at least one rule accept in
+ order to return True.
+ """
+
+ for rule in self.rules:
+ if rule(target, cred):
+ return True
+
+ return False
+
+ def add_check(self, rule):
+ """
+ Allows addition of another rule to the list of rules that will
+ be tested. Returns the OrCheck object for convenience.
+ """
+
+ self.rules.append(rule)
+ return self
+
+
+def _parse_check(rule):
+ """
+ Parse a single base check rule into an appropriate Check object.
+ """
+
+ # Handle the special checks
+ if rule == '!':
+ return FalseCheck()
+ elif rule == '@':
+ return TrueCheck()
+
+ try:
+ kind, match = rule.split(':', 1)
+ except Exception:
+ LOG.exception(_("Failed to understand rule %(rule)s") % locals())
+ # If the rule is invalid, we'll fail closed
+ return FalseCheck()
+
+ # Find what implements the check
+ if kind in _checks:
+ return _checks[kind](kind, match)
+ elif None in _checks:
+ return _checks[None](kind, match)
+ else:
+ LOG.error(_("No handler for matches of kind %s") % kind)
+ return FalseCheck()
+
+
+def _parse_list_rule(rule):
+ """
+ Provided for backwards compatibility. Translates the old
+ list-of-lists syntax into a tree of Check objects.
+ """
+
+ # Empty rule defaults to True
+ if not rule:
+ return TrueCheck()
+
+ # Outer list is joined by "or"; inner list by "and"
+ or_list = []
+ for inner_rule in rule:
+ # Elide empty inner lists
+ if not inner_rule:
+ continue
+
+ # Handle bare strings
+ if isinstance(inner_rule, basestring):
+ inner_rule = [inner_rule]
+
+ # Parse the inner rules into Check objects
+ and_list = [_parse_check(r) for r in inner_rule]
+
+ # Append the appropriate check to the or_list
+ if len(and_list) == 1:
+ or_list.append(and_list[0])
+ else:
+ or_list.append(AndCheck(and_list))
+
+ # If we have only one check, omit the "or"
+ if len(or_list) == 0:
+ return FalseCheck()
+ elif len(or_list) == 1:
+ return or_list[0]
+
+ return OrCheck(or_list)
+
+
+# Used for tokenizing the policy language
+_tokenize_re = re.compile(r'\s+')
+
+
+def _parse_tokenize(rule):
+ """
+ Tokenizer for the policy language.
+
+ Most of the single-character tokens are specified in the
+ _tokenize_re; however, parentheses need to be handled specially,
+ because they can appear inside a check string. Thankfully, those
+ parentheses that appear inside a check string can never occur at
+ the very beginning or end ("%(variable)s" is the correct syntax).
+ """
+
+ for tok in _tokenize_re.split(rule):
+ # Skip empty tokens
+ if not tok or tok.isspace():
+ continue
+
+ # Handle leading parens on the token
+ clean = tok.lstrip('(')
+ for i in range(len(tok) - len(clean)):
+ yield '(', '('
+
+ # If it was only parentheses, continue
+ if not clean:
+ continue
+ else:
+ tok = clean
+
+ # Handle trailing parens on the token
+ clean = tok.rstrip(')')
+ trail = len(tok) - len(clean)
+
+ # Yield the cleaned token
+ lowered = clean.lower()
+ if lowered in ('and', 'or', 'not'):
+ # Special tokens
+ yield lowered, clean
+ elif clean:
+ # Not a special token, but not composed solely of ')'
+ if len(tok) >= 2 and ((tok[0], tok[-1]) in
+ [('"', '"'), ("'", "'")]):
+ # It's a quoted string
+ yield 'string', tok[1:-1]
+ else:
+ yield 'check', _parse_check(clean)
+
+ # Yield the trailing parens
+ for i in range(trail):
+ yield ')', ')'
+
+
+class ParseStateMeta(type):
+ """
+ Metaclass for the ParseState class. Facilitates identifying
+ reduction methods.
+ """
+
+ def __new__(mcs, name, bases, cls_dict):
+ """
+ Create the class. Injects the 'reducers' list, a list of
+ tuples matching token sequences to the names of the
+ corresponding reduction methods.
+ """
+
+ reducers = []
+
+ for key, value in cls_dict.items():
+ if not hasattr(value, 'reducers'):
+ continue
+ for reduction in value.reducers:
+ reducers.append((reduction, key))
+
+ cls_dict['reducers'] = reducers
+
+ return super(ParseStateMeta, mcs).__new__(mcs, name, bases, cls_dict)
+
+
+def reducer(*tokens):
+ """
+ Decorator for reduction methods. Arguments are a sequence of
+ tokens, in order, which should trigger running this reduction
+ method.
+ """
+
+ def decorator(func):
+ # Make sure we have a list of reducer sequences
+ if not hasattr(func, 'reducers'):
+ func.reducers = []
+
+ # Add the tokens to the list of reducer sequences
+ func.reducers.append(list(tokens))
+
+ return func
+
+ return decorator
+
+
+class ParseState(object):
+ """
+ Implement the core of parsing the policy language. Uses a greedy
+ reduction algorithm to reduce a sequence of tokens into a single
+ terminal, the value of which will be the root of the Check tree.
+
+ Note: error reporting is rather lacking. The best we can get with
+ this parser formulation is an overall "parse failed" error.
+ Fortunately, the policy language is simple enough that this
+ shouldn't be that big a problem.
+ """
+
+ __metaclass__ = ParseStateMeta
+
+ def __init__(self):
+ """Initialize the ParseState."""
+
+ self.tokens = []
+ self.values = []
+
+ def reduce(self):
+ """
+ Perform a greedy reduction of the token stream. If a reducer
+ method matches, it will be executed, then the reduce() method
+ will be called recursively to search for any more possible
+ reductions.
+ """
+
+ for reduction, methname in self.reducers:
+ if (len(self.tokens) >= len(reduction) and
+ self.tokens[-len(reduction):] == reduction):
+ # Get the reduction method
+ meth = getattr(self, methname)
+
+ # Reduce the token stream
+ results = meth(*self.values[-len(reduction):])
+
+ # Update the tokens and values
+ self.tokens[-len(reduction):] = [r[0] for r in results]
+ self.values[-len(reduction):] = [r[1] for r in results]
+
+ # Check for any more reductions
+ return self.reduce()
+
+ def shift(self, tok, value):
+ """Adds one more token to the state. Calls reduce()."""
+
+ self.tokens.append(tok)
+ self.values.append(value)
+
+ # Do a greedy reduce...
+ self.reduce()
+
+ @property
+ def result(self):
+ """
+ Obtain the final result of the parse. Raises ValueError if
+ the parse failed to reduce to a single result.
+ """
+
+ if len(self.values) != 1:
+ raise ValueError("Could not parse rule")
+ return self.values[0]
+
+ @reducer('(', 'check', ')')
+ @reducer('(', 'and_expr', ')')
+ @reducer('(', 'or_expr', ')')
+ def _wrap_check(self, _p1, check, _p2):
+ """Turn parenthesized expressions into a 'check' token."""
+
+ return [('check', check)]
+
+ @reducer('check', 'and', 'check')
+ def _make_and_expr(self, check1, _and, check2):
+ """
+ Create an 'and_expr' from two checks joined by the 'and'
+ operator.
+ """
+
+ return [('and_expr', AndCheck([check1, check2]))]
+
+ @reducer('and_expr', 'and', 'check')
+ def _extend_and_expr(self, and_expr, _and, check):
+ """
+ Extend an 'and_expr' by adding one more check.
+ """
+
+ return [('and_expr', and_expr.add_check(check))]
+
+ @reducer('check', 'or', 'check')
+ def _make_or_expr(self, check1, _or, check2):
+ """
+ Create an 'or_expr' from two checks joined by the 'or'
+ operator.
+ """
+
+ return [('or_expr', OrCheck([check1, check2]))]
+
+ @reducer('or_expr', 'or', 'check')
+ def _extend_or_expr(self, or_expr, _or, check):
+ """
+ Extend an 'or_expr' by adding one more check.
+ """
+
+ return [('or_expr', or_expr.add_check(check))]
+
+ @reducer('not', 'check')
+ def _make_not_expr(self, _not, check):
+ """Invert the result of another check."""
+
+ return [('check', NotCheck(check))]
+
+
+def _parse_text_rule(rule):
+ """
+ Translates a policy written in the policy language into a tree of
+ Check objects.
+ """
+
+ # Empty rule means always accept
+ if not rule:
+ return TrueCheck()
+
+ # Parse the token stream
+ state = ParseState()
+ for tok, value in _parse_tokenize(rule):
+ state.shift(tok, value)
+
+ try:
+ return state.result
+ except ValueError:
+ # Couldn't parse the rule
+ LOG.exception(_("Failed to understand rule %(rule)r") % locals())
+
+ # Fail closed
+ return FalseCheck()
+
+
+def parse_rule(rule):
+ """
+ Parses a policy rule into a tree of Check objects.
+ """
+
+ # If the rule is a string, it's in the policy language
+ if isinstance(rule, basestring):
+ return _parse_text_rule(rule)
+ return _parse_list_rule(rule)
+
+
+def register(name, func=None):
+ """
+ Register a function or Check class as a policy check.
+
+ :param name: Gives the name of the check type, e.g., 'rule',
+ 'role', etc. If name is None, a default check type
+ will be registered.
+ :param func: If given, provides the function or class to register.
+ If not given, returns a function taking one argument
+ to specify the function or class to register,
+ allowing use as a decorator.
+ """
+
+ # Perform the actual decoration by registering the function or
+ # class. Returns the function or class for compliance with the
+ # decorator interface.
+ def decorator(func):
+ _checks[name] = func
+ return func
+
+ # If the function or class is given, do the registration
+ if func:
+ return decorator(func)
+
+ return decorator
+
+
+@register("rule")
+class RuleCheck(Check):
+ def __call__(self, target, creds):
+ """
+ Recursively checks credentials based on the defined rules.
+ """
+
+ try:
+ return _rules[self.match](target, creds)
+ except KeyError:
+ # We don't have any matching rule; fail closed
+ return False
+
+
+@register("role")
+class RoleCheck(Check):
+ def __call__(self, target, creds):
+ """Check that there is a matching role in the cred dict."""
+
+ return self.match.lower() in [x.lower() for x in creds['roles']]
+
+
+@register('http')
+class HttpCheck(Check):
+ def __call__(self, target, creds):
+ """
+ Check http: rules by calling to a remote server.
+
+ This example implementation simply verifies that the response
+ is exactly 'True'.
+ """
+
+ url = ('http:' + self.match) % target
+ data = {'target': jsonutils.dumps(target),
+ 'credentials': jsonutils.dumps(creds)}
+ post_data = urllib.urlencode(data)
+ f = urllib2.urlopen(url, post_data)
+ return f.read() == "True"
+
+
+@register(None)
+class GenericCheck(Check):
+ def __call__(self, target, creds):
+ """
+ Check an individual match.
+
+ Matches look like:
+
+ tenant:%(tenant_id)s
+ role:compute:admin
+ """
+
+ # TODO(termie): do dict inspection via dot syntax
+ match = self.match % target
+ if self.kind in creds:
+ return match == unicode(creds[self.kind])
+ return False
Code Review / openstack-build / heat-build.git / commitdiff