python-3.x - 使用 ctypes 检索 native 基类的地址

Question

我希望能够在不需要临时文件的情况下将证书传递给 Python 的 ssl 库。似乎 Python ssl 模块 cannot do that .

为了解决这个问题，我想检索底层 SSL_CTX结构存储在 ssl._ssl._SSLContext来自本地的类(class)_ssl模块。使用 ctypes 我可以手动调用相应的 SSL_CTX_*具有该上下文的 libssl 函数。显示了如何在 C 中执行此操作 here我会通过 ctypes 做同样的事情。

不幸的是，我被困在了我设法连接到 load_verify_locations 的地方。函数来自 ssl._ssl._SSLContext但似乎无法获得 ssl._ssl._SSLContext 实例的正确内存地址结构。所有load_verify_locations函数看到的是父 ssl.SSLContext目的。

我的问题是，我如何从 ssl.SSLContext 的实例中获取对象到 native 基类的内存ssl._ssl._SSLContext ?如果我有这个，我可以很容易地访问它的ctx成员。

到目前为止，这是我的代码。关于如何对原生 Python 模块进行猴子补丁的学分转到 the forbidden fruit project by Lincoln Clarete

Py_ssize_t = hasattr(ctypes.pythonapi, 'Py_InitModule4_64') and ctypes.c_int64 or ctypes.c_int

class PyObject(ctypes.Structure):
    pass

PyObject._fields_ = [
    ('ob_refcnt', Py_ssize_t),
    ('ob_type', ctypes.POINTER(PyObject)),
]

class SlotsProxy(PyObject):
    _fields_ = [('dict', ctypes.POINTER(PyObject))]

class PySSLContext(ctypes.Structure):
    pass

PySSLContext._fields_ = [
        ('ob_refcnt', Py_ssize_t),
        ('ob_type', ctypes.POINTER(PySSLContext)),
        ('ctx', ctypes.c_void_p),
        ]

name = ssl._ssl._SSLContext.__name__
target = ssl._ssl._SSLContext.__dict__
proxy_dict = SlotsProxy.from_address(id(target))
namespace = {}
ctypes.pythonapi.PyDict_SetItem(
        ctypes.py_object(namespace),
        ctypes.py_object(name),
        proxy_dict.dict,
)
patchable = namespace[name]

old_value = patchable["load_verify_locations"]

libssl = ctypes.cdll.LoadLibrary("libssl.so.1.0.0")
libssl.SSL_CTX_set_verify.argtypes = (ctypes.c_void_p, ctypes.c_int, ctypes.c_void_p)
libssl.SSL_CTX_get_verify_mode.argtypes = (ctypes.c_void_p,)

def load_verify_locations(self, cafile, capath, cadata):
    print(self)
    print(self.verify_mode)
    addr = PySSLContext.from_address(id(self)).ctx
    libssl.SSL_CTX_set_verify(addr, 1337, None)
    print(libssl.SSL_CTX_get_verify_mode(addr))
    print(self.verify_mode)
    return old_value(self, cafile, capath, cadata)

patchable["load_verify_locations"] = load_verify_locations

context = ssl.create_default_context(ssl.Purpose.SERVER_AUTH)

输出是:

<ssl.SSLContext object at 0x7f4b81304ba8>
2
1337
2

这表明，无论我改变什么，都不是 Python 知道的 ssl 上下文，而是其他一些随机内存位置。

要尝试上面的代码，您必须运行 https 服务器。使用以下命令生成自签名 SSL 证书:

$ openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365 -subj '/CN=localhost' -nodes

并使用以下代码启动服务器:

import http.server, http.server
import ssl
httpd = http.server.HTTPServer(('localhost', 4443), http.server.SimpleHTTPRequestHandler)
httpd.socket = ssl.wrap_socket (httpd.socket, certfile='cert.pem', keyfile='key.pem', server_side=True)
httpd.serve_forever()

然后将以下行添加到我上面的示例代码的末尾:

urllib.request.urlopen("https://localhost:4443", context=context)

Answer 1

实际 SSLContext答案即将到来，假设不再正确。

见 https://docs.python.org/3/library/ssl.html#ssl.SSLContext.load_verify_locations

还有第三个参数，cadata

The cadata object, if present, is either an ASCII string of one or more PEM-encoded certificates or a bytes-like object of DER-encoded certificates.

显然从 Python 3.4 开始就是这种情况

获取底层 PyObject 上下文

这个很简单， ssl.SSLContext继承自 _ssl._SSLContext在 Python 数据模型中，这意味着一个内存地址只有一个对象。

因此， ssl.SSLContext().load_verify_locations(...)实际上会调用:

ctx = \
ssl.SSLContext.__new__(<type ssl.SSLContext>, ...)  # which calls
    self = _ssl._SSLContext.__new__(<type ssl.SSLContext>, ...)  # which calls
        <type ssl.SSLContext>->tp_alloc()  # which understands inheritance
        self->ctx = SSL_CTX_new(...)  # _ssl fields
    self.set_ciphers(...)  # ssl fields
    return self

_ssl._SSLContext.load_verify_locations(ctx, ...)`.

C 实现会得到一个看似错误类型的对象，但这没关系，因为所有预期的字段都在那里，因为它是由泛型 type->tp_alloc 分配的。并且字段首先由 _ssl._SSLContext 填写然后由 ssl.SSLContext .

这是一个演示(省略了繁琐的细节):

# _parent.c
typedef struct {
  PyObject_HEAD
} PyParent;

static PyObject* parent_new(PyTypeObject* type, PyObject* args,
                            PyObject* kwargs) {
  PyParent* self = (PyParent*)type->tp_alloc(type, 0);
  printf("Created parent %ld\n", (long)self);
  return (PyObject*)self;
}

# child.py
class Child(_parent.Parent):
    def foo(self):
        print(id(self))

c1 = Child()
print("Created child:", id(c1))

# prints:
Created parent 139990593076080
Created child: 139990593076080

获取底层 OpenSSL 上下文

typedef struct {
    PyObject_HEAD
    SSL_CTX *ctx;
    <details skipped>
} PySSLContext;

因此， ctx位于已知偏移量处，即:

PyObject_HEAD
This is a macro which expands to the declarations of the fields of the PyObject type; it is used when declaring new types which represent objects without a varying length. The specific fields it expands to depend on the definition of Py_TRACE_REFS. By default, that macro is not defined, and PyObject_HEAD expands to:

Py_ssize_t ob_refcnt;
PyTypeObject *ob_type;

When Py_TRACE_REFS is defined, it expands to:

PyObject *_ob_next, *_ob_prev;
Py_ssize_t ob_refcnt;
PyTypeObject *ob_type;

因此，在生产(非调试)构建中，考虑到自然对齐， PySSLContext变成:

struct {
    void*;
    void*;
    SSL_CTX *ctx;
    ...
}

所以:

_ctx = _ssl._SSLContext(2)
c_ctx = ctypes.cast(id(_ctx), ctypes.POINTER(ctypes.c_void_p))
c_ctx[:3]
[1, 140486908969728, 94916219331584]
# refcnt,      type,          C ctx

把它们放在一起

import ssl
import socket
import ctypes
import pytest


def contact_github(cafile=""):
    ctx = ssl.SSLContext()
    ctx.verify_mode = ssl.VerifyMode.CERT_REQUIRED

    # ctx.load_verify_locations(cafile, "empty", None) done via ctypes
    ssl_ctx = ctypes.cast(id(ctx), ctypes.POINTER(ctypes.c_void_p))[2]
    cssl = ctypes.CDLL("/usr/lib/x86_64-linux-gnu/libssl.so.1.1")
    cssl.SSL_CTX_load_verify_locations.argtypes = [ctypes.c_void_p, ctypes.c_char_p, ctypes.c_char_p]
    assert cssl.SSL_CTX_load_verify_locations(ssl_ctx, cafile.encode("utf-8"), b"empty")

    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect(("github.com", 443))

    ss = ctx.wrap_socket(s)
    ss.send(b"GET / HTTP/1.0\n\n")
    print(ss.recv(1024))


def test_wrong_cert():
    with pytest.raises(ssl.SSLError):
        contact_github(cafile="bad-cert.pem")


def test_correct_cert():
    contact_github(cafile="good-cert.pem")