在 uvloop 中使用 os.setuid() 拒绝权限

Question

我需要运行作为 "nobody" 用户在我的主进程中创建一个子进程，代码如下：

# os.setuid(65534)  # out the set_id work fine!!

logging.warning(f"outside user: {getpass.getuser()}")
# output: outside user: root

def set_id() -> None:
    logging.warning(f"sub !sub! process user id is {os.getuid(), os.getgid(), os.getgroups()}!!!!!!!!!!!!")
    # output: root:sub !sub! process user id is (0, 0, [])!!!!!!!!!!!!
    assert os.getuid() == 0

    logging.warning(f"inside user: {getpass.getuser()}")
    # output: inside user: root

    # os.setgid(65534)  # work fine
    os.setuid(65534)  # can't work

pro = await asyncio.subprocess.create_subprocess_exec(
    # *tmp_cmd,
    "ls",
    stdout=asyncio.subprocess.PIPE,
    stdin=asyncio.subprocess.PIPE,
    stderr=asyncio.subprocess.PIPE,
    cwd=self._cwd,
    preexec_fn=set_id,
    start_new_session=True,
    close_fds=True,
)

当我调用 os.setuid(65534) 时，引发错误 PermissionError: [Errno 13] Permission denied。
但是 os.setgid(65534) 工作正常。
额外信息：

在 set_id 函数中，os.getuid(), os.getgid(), os.getgroups() 的输出是 (0, 0, [])
在 set_id 之外，os.setuid(65534) 工作正常。
getpass.getuser() == "root"

这是为什么？我怎样才能解决这个问题？提前致谢。
回溯：

ERROR:uvicorn.error:Exception in ASGI application
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/dist-packages/uvicorn/protocols/websockets/websockets_impl.py", line 153, in run_asgi
    result = await self.app(self.scope, self.asgi_receive, self.asgi_send)
  File "/usr/local/lib/python3.7/dist-packages/uvicorn/middleware/proxy_headers.py", line 45, in __call__
    return await self.app(scope, receive, send)
  File "/usr/local/lib/python3.7/dist-packages/fastapi/applications.py", line 149, in __call__
    await super().__call__(scope, receive, send)
  File "/usr/local/lib/python3.7/dist-packages/starlette/applications.py", line 102, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/usr/local/lib/python3.7/dist-packages/starlette/middleware/errors.py", line 146, in __call__
    await self.app(scope, receive, send)
  File "/usr/local/lib/python3.7/dist-packages/starlette/middleware/cors.py", line 68, in __call__
    await self.app(scope, receive, send)
  File "/usr/local/lib/python3.7/dist-packages/starlette/exceptions.py", line 58, in __call__
    await self.app(scope, receive, send)
  File "/usr/local/lib/python3.7/dist-packages/starlette/routing.py", line 550, in __call__
    await route.handle(scope, receive, send)
  File "/usr/local/lib/python3.7/dist-packages/starlette/routing.py", line 283, in handle
    await self.app(scope, receive, send)
  File "/usr/local/lib/python3.7/dist-packages/starlette/routing.py", line 57, in app
    await func(session)
  File "/usr/local/lib/python3.7/dist-packages/fastapi/routing.py", line 209, in app
    await dependant.call(**values)
  File "/opt/MakerServer/app/api/routes/websockets_runner/runner.py", line 21, in wss_back
    process = await WSProcess.create(file_m, ws=websocket)
  File "/opt/MakerServer/app/services/processer.py", line 100, in create
    self.proc: asyncio.subprocess.Process = await self._create_sub_process()  # type: ignore
  File "/opt/MakerServer/app/services/processer.py", line 136, in _create_sub_process
    close_fds=True,
  File "/usr/lib/python3.7/asyncio/subprocess.py", line 217, in create_subprocess_exec
    stderr=stderr, **kwds)
  File "uvloop/loop.pyx", line 2749, in subprocess_exec
  File "uvloop/loop.pyx", line 2707, in __subprocess_run
  File "uvloop/handles/process.pyx", line 596, in uvloop.loop.UVProcessTransport.new
  File "uvloop/handles/process.pyx", line 98, in uvloop.loop.UVProcess._init
PermissionError: [Errno 13] Permission denied

Answer 1

问题没有提供所有的要素，但这是我会看到的：

os.setuid 无法生成 13 的错误号。来自 setuid 的权限错误将是 EPERM，即错误号 1。
因此，我认为产生异常的不是 os.setuid。
我的猜测是当 Popen 尝试以用户 65534（它可能是目标可执行文件、一些库或一些在线加载的配置文件）。

如何继续解决这个问题：

通过在 os.setuid 周围添加 try catch 块来确认问题。我 99% 确定它不会触发。
然后尝试从 shell 以 su 作为 nobody 用户运行你的命令。您很可能会遇到同样的错误。

您还可以在您的程序上使用 strace -f 来查看哪个系统调用失败以及调用时使用了哪些参数。那应该会为您指明正确的方向。

在 uvloop 中使用 os.setuid() 拒绝权限

Permission denied with os.setuid() in uvloop

python

subprocess

python-os

uvicorn

uvloop