Switching groups with newgrp - how to get the new group with |GetTokenInformation()| ?

[Roland Mainz]

On Thu, Feb 22, 2024 at 8:11 PM Corinna Vinschen via Cygwin
<cygwin@cygwin.com> wrote:
> On Feb 22 18:38, Roland Mainz via Cygwin wrote:
> > If I switch the current user's group with /usr/bin/newgrp, how can a
> > (native) Win32 process use
> > |GetTokenInformation(GetCurrentThreadToken(), ...)| to find out which
> > group is the new "current group" (e.g. which |TokenInformationClass|
> > should I use) ?
>
>   PSID sidbuf = (PSID) alloca (SECURITY_MAX_SID_SIZE);
>   NTSTATUS status;
>   ULONG size;
>
>   status = NtQueryInformationToken (hProcToken, TokenPrimaryGroup,
>                                     sidbuf, SECURITY_MAX_SID_SIZE,
>                                     &size);

Well, it works in the case of an "hello world" application, but if I
stuff that into the nfsd_daemon (NFSv4.1 ms-nfs41-client client
daemon) it always prints the default primary group, even if the
current thread should impersonate another user - or in this case even
the same user, but a different primary group (e.g. see
https://github.com/kofemann/ms-nfs41-client/blob/master/sys/nfs41_driver.c#L1367).

Do you have any idea what is going wrong in this case ?

----

Bye,
Roland
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