Python eval：如果我禁用内置函数和属性访问，这仍然很危险吗？ [英] Python eval: is it still dangerous if I disable builtins and attribute access?

问题描述

我们都知道 eval 是危险的，即使您隐藏了危险的函数，因为您可以使用Python的自省功能深入挖掘并重新提取它们。例如，即使删除 __ builtins __ ，也可以使用

We all know that eval is dangerous, even if you hide dangerous functions, because you can use Python's introspection features to dig down into things and re-extract them. For example, even if you delete __builtins__, you can retrieve them with

[c for c in ().__class__.__base__.__subclasses__()  
 if c.__name__ == 'catch_warnings'][0]()._module.__builtins__

但是，我所看到的每个示例都使用属性访问。如果我禁用所有内置函数，和禁用属性访问（通过使用Python标记器标记输入并在具有属性访问标记的情况下拒绝输入，该怎么办）？

However, every example I've seen of this uses attribute access. What if I disable all builtins, and disable attribute access (by tokenizing the input with a Python tokenizer and rejecting it if it has an attribute access token)?

在您问不，在我的用例中，我不需要这两个，所以它不会太残废。

And before you ask, no, for my use-case, I do not need either of these, so it isn't too crippling.

我要做的是使SymPy的 sympify 功能更安全。当前，它对输入进行标记化，对其进行一些转换，然后在名称空间中进行评估。但这是不安全的，因为它允许属性访问（即使确实不需要）。

What I'm trying to do is make SymPy's sympify function more safe. Currently it tokenizes the input, does some transformations on it, and evals it in a namespace. But it's unsafe because it allows attribute access (even though it really doesn't need it).

推荐答案

我要提及Python 3.6的新功能之一- f-strings 。

I'm going to mention one of the new features of Python 3.6 - f-strings.

他们可以计算表达式，

>>> eval('f"{().__class__.__base__}"', {'__builtins__': None}, {})
"<class 'object'>"

，但是Python的标记器不会检测到属性访问：

but the attribute access won't be detected by Python's tokenizer:

0,0-0,0:            ENCODING       'utf-8'        
1,0-1,1:            ERRORTOKEN     "'"            
1,1-1,27:           STRING         'f"{().__class__.__base__}"'
2,0-2,0:            ENDMARKER      '' 

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