# -*- coding: utf-8 -*-
##############################################################################
#    Copyright (C) 2004-2012 OpenERP s.a. (<http://www.openerp.com>).
#
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU Affero General Public License as
#    published by the Free Software Foundation, either version 3 of the
#    License, or (at your option) any later version.
#
#    This program 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 Affero General Public License for more details.
#
#    You should have received a copy of the GNU Affero General Public License
#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
##############################################################################

"""
safe_eval module - methods intended to provide more restricted alternatives to
                   evaluate simple and/or untrusted code.

Methods in this module are typically used as alternatives to eval() to parse
OpenERP domain strings, conditions and expressions, mostly based on locals
condition/math builtins.
"""

# Module partially ripped from/inspired by several different sources:
#  - http://code.activestate.com/recipes/286134/
#  - safe_eval in lp:~xrg/openobject-server/optimize-5.0
#  - safe_eval in tryton http://hg.tryton.org/hgwebdir.cgi/trytond/rev/bbb5f73319ad

from opcode import HAVE_ARGUMENT, opmap, opname
from types import CodeType
import logging

__all__ = ['test_expr', 'safe_eval', 'const_eval']

# The time module is usually already provided in the safe_eval environment
# but some code, e.g. datetime.datetime.now() (Windows/Python 2.5.2, bug
# lp:703841), does import time.
_ALLOWED_MODULES = ['_strptime', 'time']

_CONST_OPCODES = set(opmap[x] for x in [
    'POP_TOP', 'ROT_TWO', 'ROT_THREE', 'ROT_FOUR', 'DUP_TOP', 'DUP_TOPX',
    'POP_BLOCK','SETUP_LOOP', 'BUILD_LIST', 'BUILD_MAP', 'BUILD_TUPLE',
    'LOAD_CONST', 'RETURN_VALUE', 'STORE_SUBSCR', 'STORE_MAP'] if x in opmap)

_EXPR_OPCODES = _CONST_OPCODES.union(set(opmap[x] for x in [
    'UNARY_POSITIVE', 'UNARY_NEGATIVE', 'UNARY_NOT',
    'UNARY_INVERT', 'BINARY_POWER', 'BINARY_MULTIPLY',
    'BINARY_DIVIDE', 'BINARY_FLOOR_DIVIDE', 'BINARY_TRUE_DIVIDE',
    'BINARY_MODULO', 'BINARY_ADD', 'BINARY_SUBTRACT', 'BINARY_SUBSCR',
    'BINARY_LSHIFT', 'BINARY_RSHIFT', 'BINARY_AND', 'BINARY_XOR',
    'BINARY_OR', 'INPLACE_ADD', 'INPLACE_SUBTRACT', 'INPLACE_MULTIPLY',
    'INPLACE_DIVIDE', 'INPLACE_REMAINDER', 'INPLACE_POWER',
    'INPLACE_LEFTSHIFT', 'INPLACE_RIGHTSHIFT', 'INPLACE_AND',
    'INPLACE_XOR','INPLACE_OR'
    ] if x in opmap))

_SAFE_OPCODES = _EXPR_OPCODES.union(set(opmap[x] for x in [
    'LOAD_NAME', 'CALL_FUNCTION', 'COMPARE_OP', 'LOAD_ATTR',
    'STORE_NAME', 'GET_ITER', 'FOR_ITER', 'LIST_APPEND', 'DELETE_NAME',
    'JUMP_FORWARD', 'JUMP_IF_TRUE', 'JUMP_IF_FALSE', 'JUMP_ABSOLUTE',
    'MAKE_FUNCTION', 'SLICE+0', 'SLICE+1', 'SLICE+2', 'SLICE+3',
    # New in Python 2.7 - http://bugs.python.org/issue4715 :
    'JUMP_IF_FALSE_OR_POP', 'JUMP_IF_TRUE_OR_POP', 'POP_JUMP_IF_FALSE',
    'POP_JUMP_IF_TRUE', 'SETUP_EXCEPT', 'END_FINALLY',
    'LOAD_FAST', 'STORE_FAST', 'DELETE_FAST',
    'LOAD_GLOBAL', # Only allows access to restricted globals
    ] if x in opmap))

_logger = logging.getLogger(__name__)

def _get_opcodes(codeobj):
    """_get_opcodes(codeobj) -> [opcodes]

    Extract the actual opcodes as a list from a code object

    >>> c = compile("[1 + 2, (1,2)]", "", "eval")
    >>> _get_opcodes(c)
    [100, 100, 23, 100, 100, 102, 103, 83]
    """
    i = 0
    byte_codes = codeobj.co_code
    while i < len(byte_codes):
        code = ord(byte_codes[i])
        yield code

        if code >= HAVE_ARGUMENT:
            i += 3
        else:
            i += 1

def assert_no_dunder_name(code_obj, expr):
    """ assert_no_dunder_name(code_obj, expr) -> None

    Asserts that the code object does not refer to any "dunder name"
    (__$name__), so that safe_eval prevents access to any internal-ish Python
    attribute or method (both are loaded via LOAD_ATTR which uses a name, not a
    const or a var).

    Checks that no such name exists in the provided code object (co_names).

    :param code_obj: code object to name-validate
    :type code_obj: CodeType
    :param str expr: expression corresponding to the code object, for debugging
                     purposes
    :raises NameError: in case a forbidden name (containing two underscores)
                       is found in ``code_obj``

    .. note:: actually forbids every name containing 2 underscores
    """
    for name in code_obj.co_names:
        if "__" in name:
            raise NameError('Access to forbidden name %r (%r)' % (name, expr))

def assert_valid_codeobj(allowed_codes, code_obj, expr):
    """ Asserts that the provided code object validates against the bytecode
    and name constraints.

    Recursively validates the code objects stored in its co_consts in case
    lambdas are being created/used (lambdas generate their own separated code
    objects and don't live in the root one)

    :param allowed_codes: list of permissible bytecode instructions
    :type allowed_codes: set(int)
    :param code_obj: code object to name-validate
    :type code_obj: CodeType
    :param str expr: expression corresponding to the code object, for debugging
                     purposes
    :raises ValueError: in case of forbidden bytecode in ``code_obj``
    :raises NameError: in case a forbidden name (containing two underscores)
                       is found in ``code_obj``
    """
    assert_no_dunder_name(code_obj, expr)
    for opcode in _get_opcodes(code_obj):
        if opcode not in allowed_codes:
            raise ValueError(
                "opcode %s not allowed (%r)" % (opname[opcode], expr))
    for const in code_obj.co_consts:
        if isinstance(const, CodeType):
            assert_valid_codeobj(allowed_codes, const, 'lambda')

def test_expr(expr, allowed_codes, mode="eval"):
    """test_expr(expression, allowed_codes[, mode]) -> code_object

    Test that the expression contains only the allowed opcodes.
    If the expression is valid and contains only allowed codes,
    return the compiled code object.
    Otherwise raise a ValueError, a Syntax Error or TypeError accordingly.
    """
    try:
        if mode == 'eval':
            # eval() does not like leading/trailing whitespace
            expr = expr.strip()
        code_obj = compile(expr, "", mode)
    except (SyntaxError, TypeError, ValueError):
        _logger.debug('Invalid eval expression', exc_info=True)
        raise
    except Exception:
        _logger.debug('Disallowed or invalid eval expression', exc_info=True)
        raise ValueError("%s is not a valid expression" % expr)

    assert_valid_codeobj(allowed_codes, code_obj, expr)
    return code_obj


def const_eval(expr):
    """const_eval(expression) -> value

    Safe Python constant evaluation

    Evaluates a string that contains an expression describing
    a Python constant. Strings that are not valid Python expressions
    or that contain other code besides the constant raise ValueError.

    >>> const_eval("10")
    10
    >>> const_eval("[1,2, (3,4), {'foo':'bar'}]")
    [1, 2, (3, 4), {'foo': 'bar'}]
    >>> const_eval("1+2")
    Traceback (most recent call last):
    ...
    ValueError: opcode BINARY_ADD not allowed
    """
    c = test_expr(expr, _CONST_OPCODES)
    return eval(c)

def expr_eval(expr):
    """expr_eval(expression) -> value

    Restricted Python expression evaluation

    Evaluates a string that contains an expression that only
    uses Python constants. This can be used to e.g. evaluate
    a numerical expression from an untrusted source.

    >>> expr_eval("1+2")
    3
    >>> expr_eval("[1,2]*2")
    [1, 2, 1, 2]
    >>> expr_eval("__import__('sys').modules")
    Traceback (most recent call last):
    ...
    ValueError: opcode LOAD_NAME not allowed
    """
    c = test_expr(expr, _EXPR_OPCODES)
    return eval(c)

def _import(name, globals=None, locals=None, fromlist=None, level=-1):
    if globals is None:
        globals = {}
    if locals is None:
        locals = {}
    if fromlist is None:
        fromlist = []
    if name in _ALLOWED_MODULES:
        return __import__(name, globals, locals, level)
    raise ImportError(name)

def safe_eval(expr, globals_dict=None, locals_dict=None, mode="eval", nocopy=False):
    """safe_eval(expression[, globals[, locals[, mode[, nocopy]]]]) -> result

    System-restricted Python expression evaluation

    Evaluates a string that contains an expression that mostly
    uses Python constants, arithmetic expressions and the
    objects directly provided in context.

    This can be used to e.g. evaluate
    an OpenERP domain expression from an untrusted source.

    :throws TypeError: If the expression provided is a code object
    :throws SyntaxError: If the expression provided is not valid Python
    :throws NameError: If the expression provided accesses forbidden names
    :throws ValueError: If the expression provided uses forbidden bytecode
    """
    if isinstance(expr, CodeType):
        raise TypeError("safe_eval does not allow direct evaluation of code objects.")

    if globals_dict is None:
        globals_dict = {}

    # prevent altering the globals/locals from within the sandbox
    # by taking a copy.
    if not nocopy:
        # isinstance() does not work below, we want *exactly* the dict class
        if (globals_dict is not None and type(globals_dict) is not dict) \
            or (locals_dict is not None and type(locals_dict) is not dict):
            _logger.warning(
                "Looks like you are trying to pass a dynamic environment, "
                "you should probably pass nocopy=True to safe_eval().")

        globals_dict = dict(globals_dict)
        if locals_dict is not None:
            locals_dict = dict(locals_dict)

    globals_dict.update(
            __builtins__ = {
                '__import__': _import,
                'True': True,
                'False': False,
                'None': None,
                'str': str,
                'globals': locals,
                'locals': locals,
                'bool': bool,
                'dict': dict,
                'list': list,
                'tuple': tuple,
                'map': map,
                'abs': abs,
                'min': min,
                'max': max,
                'reduce': reduce,
                'filter': filter,
                'round': round,
                'len': len,
                'set' : set
            }
    )
    try:
        return eval(test_expr(expr, _SAFE_OPCODES, mode=mode), globals_dict, locals_dict)
    except Exception:
        _logger.exception('Cannot eval %r', expr)
        raise

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