From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.atof.net (smtp1.atof.net [52.86.233.228]) by sourceware.org (Postfix) with ESMTPS id 71DFB3858D39 for ; Sun, 25 Feb 2024 22:32:32 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 71DFB3858D39 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=gluelogic.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=gluelogic.com ARC-Filter: OpenARC Filter v1.0.0 sourceware.org 71DFB3858D39 Authentication-Results: server2.sourceware.org; arc=none smtp.remote-ip=52.86.233.228 ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1708900448; cv=none; b=w0EVlV3ozgKqrd878bcUi/ksYpuPzjCKtG9xIZ+oq10ybx7mVhTDtlKTDwl/YhAtF5mDGl/Nm8y0pGdM6Sw0mAJi5uk2Q6nBI9Fuo+ahMol1OXO6Dt0zv6he2OtCKelfzu1YiBtGGn6YDtkzOtYL1e1vaP+DTJ90j7LugTu92tA= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1708900448; c=relaxed/simple; bh=IzIoz/Xm+Cj0Gd8VqFMKxBqt65EAlqxA7A7ObXuVHQo=; h=Date:From:To:Subject:Message-ID:MIME-Version; b=ZrfFHjaQs1r8ZQLOPh8Gz7gC6qfytsSdkM+vyrPUYgXVoHMUIoaK+LLQSOMlmad/PiZu8R23Gr9beqSrDvR2tGySggUlvp7/KutziFGJwmB8h21UUQ6t613dNCqUzB+6beI2A5uRbT1LNkCjPpz+cG0HV295TuUajoHRhCaVHaI= ARC-Authentication-Results: i=1; server2.sourceware.org X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-Spam-Language: en X-Spam-Relay-Country: X-Spam-DCC: B=www.nova53.net; R=smtp1.atof.net 1206; Body=1 Fuz1=1 Fuz2=1 X-Spam-RBL: X-Spam-PYZOR: Reported 0 times. Date: Sun, 25 Feb 2024 17:32:22 -0500 From: gs-cygwin.com@gluelogic.com To: Roland Mainz Cc: cygwin@cygwin.com Subject: Re: Will all SIDs fit into |SECURITY_MAX_SID_SIZE| bytes ? / was: Re: Switching groups with newgrp - how to get the new group with |GetTokenInformation()| ? Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,KAM_DMARC_STATUS,SPF_HELO_NONE,SPF_PASS,TIME_LIMIT_EXCEEDED,TXREP,T_SCC_BODY_TEXT_LINE autolearn=unavailable version=3.4.6 List-Id: On Sun, Feb 25, 2024 at 10:04:29PM +0100, Roland Mainz via Cygwin wrote: > On Sat, Feb 24, 2024 at 7:57 PM Corinna Vinschen via Cygwin > wrote: > > > > On Feb 24 15:38, Roland Mainz via Cygwin wrote: > > > On Thu, Feb 22, 2024 at 8:11 PM Corinna Vinschen via Cygwin > > > 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); > > > [snip] > > > > > > Win32/NT API question: All known SIDs will fit into > > > |SECURITY_MAX_SID_SIZE| bytes, right ? I'm asking because right now > > > the ms-nfs41-client code assumes that all SIDs use a variable amount > > > of memory, and we always have to ask the Win32/NT API about the number > > > of bytes to allocate. If |SECURITY_MAX_SID_SIZE| is the global maximum > > > limit for all Windows versions, then we could simplify the code a > > > lot... > > > > Yes. ACLs are size restricted to 64K, though, but that shouldn't be > > much of a problem usally. > > Erm... why ACLs? I was asking about the memory allocation size for an SID. > > Example: > Right now our code uses two calls to |LookupAccountNameA()| for the > conversion from a Windows account name to Windows SID. > The first call gets the allocation size for a SID, our code then > allocates that memory, and then does a second call to > |LookupAccountNameA()| to fill that memory with that SID. > > If |SECURITY_MAX_SID_SIZE| (currently 68 bytes) is the maximum memory > size a Windows syscall can return for a SID, then the code above could > be simplified to a |sidmem = > malloc(SECURITY_MAX_SID_SIZE)|+|LookupAccountNameA(..., sidmem, ...)|. > > The same could be done in many many other places, leading to a > considerable reduction of Win32 system library calls. > > Question is whether the assumption about |SECURITY_MAX_SID_SIZE| is correct... A robust solution which also reduces syscalls does not necessarily require a precise answer here. I suggest writing a wrapper function which has on the stack CSTR sidbuf[SECURITY_MAX_SID_SIZE]; and calls LookupAccountNameA() passing sidbuf as Sid. If it succeeds, then malloc() returned cbSid value and copy sidbuf[]. If it fails because the buffer is too small, then malloc() the returned cbSid value and call LookupAccountNameA() again. Doing the above will keep memory use to a minimum, and will generally call LookupAccountNameA() once per wrapper func invocation rather than twice. Cheers, Glenn