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#15261 shows us that Windows can crash if you pass in an invalid file handle to Windows POSIX-y functions. We should ensure that functions which accept path-as-an-int-fd guard against this where necessary.
I propose a macro, something like
#ifdef MS_WINDOWS
#define FD_GUARD(fd) (_PyVerify_fd(fd) ? (fd) : INVALID_HANDLE_VALUE)
#else
#define FD_GUARD(fd) (fd)
#endif

Which other functions are you thinking about?

Windows will also crash if you pass INVALID_HANDLE_VALUE (which is not a file descriptor) to crt functions...
How did you want to use this macro?

Antoine: all the functions enumerated in os.supports_fd. Note that the set of such functions may in fact just be os.stat which is already fixed.
Amaury: If you read the checkin that fixes this problem ( 62b9bfbc3356 ) it actually deliberately passes in INVALID_HANDLE_VALUE to win32_fstat. I admit that's kind of where I lost interest. I'm not really a Windows developer anymore, so maybe somebody else should do it. So I have given myself a demotion; I am no longer assigned the bug.

> Antoine: all the functions enumerated in os.supports_fd. Note that the 
> set of such functions may in fact just be os.stat which is already fixed.
As far as I can tell, it is:
>>> os.supports_fd
{<built-in function stat>}

Every use of _get_osfhandle() should be guarded by _Py_VerifyFd(). 
Grepping through the source it seems that that is now true, but we could instead use
 #define _PY_GET_OSFHANDLE(fd) _Py_VerifyFd(fd) ? _get_osfhandle(fd) : INVALID_HANDLE_VALUE

I don't see any _Py_VerifyFd in the code, is this out of date?

> I don't see any _Py_VerifyFd in the code, is this out of date?
Yes, this issue is out of date. The underlying issue is that the C runtime in Windows automatically checks various parameters and calls a registered handler for invalid parameters, for which the default handler terminates the process. Python 3.5+ uses a new C runtime (ucrt), which supports setting a handler for just the current thread, so this issue is addressed more generally nowadays by the macros _Py_BEGIN_SUPPRESS_IPH and _Py_END_SUPPRESS_IPH.