[Bug check/report] UnDocumented call to ntdll.dll!NtAssignProcessToJobObject in msys2.0.dll / cygwin - included in mingit/Git for Windows

[Johannes Schindelin]

Hi Veronica & Cygwin list (please keep me Cc:ed, I am not subscribed),

On Sat, 11 Jan 2025, Veronica Giaudrone wrote:

> I'm part of the Visual Studio team at Microsoft which includes
> mingit/Git for Windows in our product for Git tooling integration (I'm
> copying a couple of folks from my team in this email too). One of our
> API scanning tools has identified msys2.0.dll calling undocumented
> Windows APIs like ntdll.dll!NtAssignProcessToJobObject:
>
>   *   In cygwin -
>       https://github.com/search?q=repo%3Acygwin%2Fcygwin+NtAssignProcessToJobObject&type=code
>       with a caller: cygwin/winsup/cygwin/resource.cc at
>       21a2c9db6952954608cdf92638b411b15e7606c6 *
>       cygwin/cygwin<https://github.com/cygwin/cygwin/blob/21a2c9db6952954608cdf92638b411b15e7606c6/winsup/cygwin/resource.cc#L246>
>   *   Looks like it was introduced ~3 years ago:
>       https://github.com/cygwin/cygwin/commit/1c7384f9d1b692c8b58af4db8c81d2ce0b10ad06#diff-bc84d57ac99958a694cb56b977bac1360e35040f9aa421972702219e11055ae8R290
>   *   The code indicates to have come from
>       oneTBB/test/tbbmalloc/test_malloc_compliance.cpp at
>       bd291eb0d1c7f802ca5081a8755562ab786db2a2 *
>       uxlfoundation/oneTBB<https://github.com/uxlfoundation/oneTBB/blob/bd291eb0d1c7f802ca5081a8755562ab786db2a2/test/tbbmalloc/test_malloc_compliance.cpp#L56-L78>,
>       though in that case the usage is of the documented API instead.
>
> We believe the above call should get replaced by the following
> documented API - AssignProcessToJobObject function (jobapi2.h) - Win32
> apps | Microsoft
> Learn<https://learn.microsoft.com/en-us/windows/win32/api/jobapi2/nf-jobapi2-assignprocesstojobobject>
>
> Are you aware of this undocumented API call or a reason to not attempt updating them to documented ones?
>
> The scan identified a few others like:
>
>   *   NtOpenJobObject
>   *   NtCreateJobObject
>   *   NtQueryInformationJobObject
>   *   NtSetInformationJobObject

These seem to have been introduced in the very same commit as
`NtAssignProcessToJobObject()`.

Seeing as the original code on oneBB did not require undocumented function
calls, I could imagine that it might be an obvious and uncontroversial
change to use documented functions.

>   *   NtOpenMutant - we're not sure yet of the documented call for this one.

There are multiple mentions of this (and of `NtCreateMutant()`, also an
undocumented function) in Cygwin's source code, most notably in
`winsup/cygwin/kernel32.cc`, where the `CreateMutexW()` and `OpenMutexW()`
function are reimplemented, preceded with this informative comment:

	/* Implement CreateMutex/OpenMutex so that named objects are
	 * always created in Cygwin shared object namespace. */

Specifically, if `NULL` was passed in as `lpName`, the code calls
`InitializeObjectAttributes()` with `get_shared_parent_dir()` as root
object directory.

I am too unfamiliar with such internals to tell whether there is a way to
accomplish this exclusively using documented functions.

Ciao,
Johannes