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# (c) 2012, Michael DeHaan <michael.dehaan@gmail.com>
#
# This file is part of Ansible
#
# Ansible is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# Ansible is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Ansible. If not, see <http://www.gnu.org/licenses/>.
from __future__ import (absolute_import, division, print_function)
__metaclass__ = type
import ast
import sys
from ansible import constants as C
from ansible.module_utils.common.text.converters import container_to_text, to_native
from ansible.module_utils.six import string_types, PY2
from ansible.module_utils.six.moves import builtins
from ansible.plugins.loader import filter_loader, test_loader
def safe_eval(expr, locals=None, include_exceptions=False):
'''
This is intended for allowing things like:
with_items: a_list_variable
Where Jinja2 would return a string but we do not want to allow it to
call functions (outside of Jinja2, where the env is constrained).
Based on:
http://stackoverflow.com/questions/12523516/using-ast-and-whitelists-to-make-pythons-eval-safe
'''
locals = {} if locals is None else locals
# define certain JSON types
# eg. JSON booleans are unknown to python eval()
OUR_GLOBALS = {
'__builtins__': {}, # avoid global builtins as per eval docs
'false': False,
'null': None,
'true': True,
# also add back some builtins we do need
'True': True,
'False': False,
'None': None
}
# this is the whitelist of AST nodes we are going to
# allow in the evaluation. Any node type other than
# those listed here will raise an exception in our custom
# visitor class defined below.
SAFE_NODES = set(
(
ast.Add,
ast.BinOp,
# ast.Call,
ast.Compare,
ast.Dict,
ast.Div,
ast.Expression,
ast.List,
ast.Load,
ast.Mult,
ast.Num,
ast.Name,
ast.Str,
ast.Sub,
ast.USub,
ast.Tuple,
ast.UnaryOp,
)
)
# AST node types were expanded after 2.6
if sys.version_info[:2] >= (2, 7):
SAFE_NODES.update(
set(
(ast.Set,)
)
)
# And in Python 3.4 too
if sys.version_info[:2] >= (3, 4):
SAFE_NODES.update(
set(
(ast.NameConstant,)
)
)
# And in Python 3.6 too, although not encountered until Python 3.8, see https://bugs.python.org/issue32892
if sys.version_info[:2] >= (3, 6):
SAFE_NODES.update(
set(
(ast.Constant,)
)
)
filter_list = []
for filter_ in filter_loader.all():
filter_list.extend(filter_.filters().keys())
test_list = []
for test in test_loader.all():
test_list.extend(test.tests().keys())
CALL_ENABLED = C.CALLABLE_ACCEPT_LIST + filter_list + test_list
class CleansingNodeVisitor(ast.NodeVisitor):
def generic_visit(self, node, inside_call=False):
if type(node) not in SAFE_NODES:
raise Exception("invalid expression (%s)" % expr)
elif isinstance(node, ast.Call):
inside_call = True
elif isinstance(node, ast.Name) and inside_call:
# Disallow calls to builtin functions that we have not vetted
# as safe. Other functions are excluded by setting locals in
# the call to eval() later on
if hasattr(builtins, node.id) and node.id not in CALL_ENABLED:
raise Exception("invalid function: %s" % node.id)
# iterate over all child nodes
for child_node in ast.iter_child_nodes(node):
self.generic_visit(child_node, inside_call)
if not isinstance(expr, string_types):
# already templated to a datastructure, perhaps?
if include_exceptions:
return (expr, None)
return expr
cnv = CleansingNodeVisitor()
try:
parsed_tree = ast.parse(expr, mode='eval')
cnv.visit(parsed_tree)
compiled = compile(parsed_tree, '<expr %s>' % to_native(expr), 'eval')
# Note: passing our own globals and locals here constrains what
# callables (and other identifiers) are recognized. this is in
# addition to the filtering of builtins done in CleansingNodeVisitor
result = eval(compiled, OUR_GLOBALS, dict(locals))
if PY2:
# On Python 2 u"{'key': 'value'}" is evaluated to {'key': 'value'},
# ensure it is converted to {u'key': u'value'}.
result = container_to_text(result)
if include_exceptions:
return (result, None)
else:
return result
except SyntaxError as e:
# special handling for syntax errors, we just return
# the expression string back as-is to support late evaluation
if include_exceptions:
return (expr, None)
return expr
except Exception as e:
if include_exceptions:
return (expr, e)
return expr
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