1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
|
from __future__ import division
_const_codes = [
'POP_TOP','ROT_TWO','ROT_THREE','ROT_FOUR','DUP_TOP',
'BUILD_LIST','BUILD_MAP', 'MAP_ADD', 'BUILD_TUPLE','BUILD_SET',
'BUILD_CONST_KEY_MAP', 'BUILD_STRING',
'LOAD_CONST','RETURN_VALUE','STORE_SUBSCR', 'STORE_MAP',
'LIST_TO_TUPLE', 'LIST_EXTEND', 'SET_UPDATE', 'DICT_UPDATE', 'DICT_MERGE',
'COPY', 'RESUME', 'RETURN_CONST'
]
_expr_codes = _const_codes + [
'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_LSHIFT','BINARY_RSHIFT','BINARY_AND','BINARY_XOR',
'BINARY_OR',
'BINARY_OP',
]
_values_codes = _expr_codes + ['LOAD_NAME']
import six
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) # doctest: +ELLIPSIS
[...100, 100, 103, 83]
"""
import dis
if hasattr(dis, 'get_instructions'):
return [ins.opcode for ins in dis.get_instructions(codeobj)]
i = 0
opcodes = []
s = codeobj.co_code
while i < len(s):
code = six.indexbytes(s, i)
opcodes.append(code)
if code >= dis.HAVE_ARGUMENT:
i += 3
else:
i += 1
return opcodes
def test_expr(expr, allowed_codes):
"""test_expr(expr, allowed_codes) -> codeobj
Test that the expression contains only the listed opcodes.
If the expression is valid and contains only allowed codes,
return the compiled code object. Otherwise raise a ValueError
"""
import dis
allowed_codes = [dis.opmap[c] for c in allowed_codes if c in dis.opmap]
try:
c = compile(expr, "", "eval")
except SyntaxError:
raise ValueError("%r is not a valid expression" % expr)
codes = _get_opcodes(c)
for code in codes:
if code not in allowed_codes:
raise ValueError("opcode %s not allowed" % dis.opname[code])
return c
def const(expr):
"""const(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.
Examples:
>>> const("10")
10
>>> const("[1,2, (3,4), {'foo':'bar'}]")
[1, 2, (3, 4), {'foo': 'bar'}]
>>> const("[1]+[2]")
Traceback (most recent call last):
...
ValueError: opcode BINARY_ADD not allowed
"""
c = test_expr(expr, _const_codes)
return eval(c)
def expr(expr):
"""expr(expression) -> value
Safe 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.
Examples:
>>> expr("1+2")
3
>>> expr("[1,2]*2")
[1, 2, 1, 2]
>>> expr("__import__('sys').modules")
Traceback (most recent call last):
...
ValueError: opcode LOAD_NAME not allowed
"""
c = test_expr(expr, _expr_codes)
return eval(c)
def values(expr, env):
"""values(expression, dict) -> value
Safe Python expression evaluation
Evaluates a string that contains an expression that only
uses Python constants and values from a supplied dictionary.
This can be used to e.g. evaluate e.g. an argument to a syscall.
Note: This is potentially unsafe if e.g. the __add__ method has side
effects.
Examples:
>>> values("A + 4", {'A': 6})
10
>>> class Foo:
... def __add__(self, other):
... print("Firing the missiles")
>>> values("A + 1", {'A': Foo()})
Firing the missiles
>>> values("A.x", {'A': Foo()})
Traceback (most recent call last):
...
ValueError: opcode LOAD_ATTR not allowed
"""
# The caller might need his dictionary again
env = dict(env)
# We do not want to have built-ins set
env['__builtins__'] = {}
c = test_expr(expr, _values_codes)
return eval(c, env)
|
