Commit Graph

49 Commits

Author SHA1 Message Date
Aaron Klotz
b292f7f9ac util/winutil/s4u: fix incorrect token type specified in s4u Login
This was correct before, I think I just made a copy/paste error when
updating that PR.

Updates #12383

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2024-06-26 14:28:56 -06:00
Aaron Klotz
5f177090e3 util/winutil: ensure domain controller address is used when retrieving remote profile information
We cannot directly pass a flat domain name into NetUserGetInfo; we must
resolve the address of a domain controller first.

This PR implements the appropriate resolution mechanisms to do that, and
also exposes a couple of new utility APIs for future needs.

Fixes #12627

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2024-06-26 13:10:10 -06:00
Aaron Klotz
da078b4c09 util/winutil: add package for logging into Windows via Service-for-User (S4U)
This PR ties together pseudoconsoles, user profiles, s4u logons, and
process creation into what is (hopefully) a simple API for various
Tailscale services to obtain Windows access tokens without requiring
knowledge of any Windows passwords. It works both for domain-joined
machines (Kerberos) and non-domain-joined machines. The former case
is fairly straightforward as it is fully documented. OTOH, the latter
case is not documented, though it is fully defined in the C headers in
the Windows SDK. The documentation blanks were filled in by reading
the source code of Microsoft's Win32 port of OpenSSH.

We need to do a bit of acrobatics to make conpty work correctly while
creating a child process with an s4u token; see the doc comments above
startProcessInternal for details.

Updates #12383

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2024-06-25 22:05:52 -06:00
Aaron Klotz
7354547bd8 util/winutil: update UserProfile to ensure any environment variables in the roaming profile path are expanded
Updates #12383

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2024-06-14 13:01:01 -06:00
Aaron Klotz
bd2a6d5386 util/winutil: add UserProfile type for (un)loading user profiles
S4U logons do not automatically load the associated user profile. In this
PR we add UserProfile to handle that part. Windows docs indicate that
we should try to resolve a remote profile path when present, so we attempt
to do so when the local computer is joined to a domain.

Updates #12383

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2024-06-14 11:02:01 -06:00
Aaron Klotz
df86576989 util/winutil: add AllocateContiguousBuffer and SetNTString helper funcs
AllocateContiguousBuffer is for allocating structs with trailing buffers
containing additional data. It is to be used for various Windows structures
containing pointers to data located immediately after the struct.

SetNTString performs in-place setting of windows.NTString and
windows.NTUnicodeString.

Updates #12383

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2024-06-10 09:39:37 -06:00
Aaron Klotz
34e8820301 util/winutil: add conpty package and helper for building windows.StartupInfoEx
StartupInfoBuilder is a helper for constructing StartupInfoEx structures
featuring proc/thread attribute lists. Calling its setters triggers the
appropriate setting of fields, adjusting flags as necessary, and populating
the proc/thread attribute list as necessary. Currently it supports four
features: setting std handles, setting pseudo-consoles, specifying handles
for inheritance, and specifying jobs.

The conpty package simplifies creation of pseudo-consoles, their associated
pipes, and assignment of the pty to StartupInfoEx proc/thread attributes.

Updates #12383

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2024-06-06 14:18:36 -06:00
Andrea Gottardo
1d3e77f373
util/syspolicy: add ReadStringArray interface (#11857)
Fixes tailscale/corp#19459

This PR adds the ability for users of the syspolicy handler to read string arrays from the MDM solution configured on the system.

Signed-off-by: Andrea Gottardo <andrea@gottardo.me>
2024-04-23 22:23:48 -07:00
Brad Fitzpatrick
7c1d6e35a5 all: use Go 1.22 range-over-int
Updates #11058

Change-Id: I35e7ef9b90e83cac04ca93fd964ad00ed5b48430
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
2024-04-16 15:32:38 -07:00
Nick Khyl
8d83adde07 util/winutil/winenv: add package for current Windows environment details
Package winenv provides information about the current Windows environment.
This includes details such as whether the device is a server or workstation,
and if it is AD domain-joined, MDM-registered, or neither.

Updates tailscale/corp#18342

Signed-off-by: Nick Khyl <nickk@tailscale.com>
2024-04-09 13:25:37 -05:00
Aaron Klotz
aed2cfec4e util/winutil: add some missing docs to restartmgr errors
Just a quick #cleanup.

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2024-01-05 10:12:08 -08:00
Aaron Klotz
5812093d31 util/winutil: publicize existing functions for opening read-only connections to the Windows Service Control Manager
We're going to need to access these from code outside winutil.

Updates #10215

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2023-12-22 10:52:50 -08:00
Andrew Lytvynov
2716250ee8
all: cleanup unused code, part 2 (#10670)
And enable U1000 check in staticcheck.

Updates #cleanup

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>
2023-12-21 17:40:03 -08:00
Aaron Klotz
db39a43f06 util/winutil: add support for restarting Windows processes in specific sessions
This PR is all about adding functionality that will enable the installer's
upgrade sequence to terminate processes belonging to the previous version,
and then subsequently restart instances belonging to the new version within
the session(s) corresponding to the processes that were killed.

There are multiple parts to this:

* We add support for the Restart Manager APIs, which allow us to query the
  OS for a list of processes locking specific files;
* We add the RestartableProcess and RestartableProcesses types that query
  additional information about the running processes that will allow us
  to correctly restart them in the future. These types also provide the
  ability to terminate the processes.
* We add the StartProcessInSession family of APIs that permit us to create
  new processes within specific sessions. This is needed in order to
  properly attach a new GUI process to the same RDP session and desktop that
  its previously-terminated counterpart would have been running in.
* I tweaked the winutil token APIs again.
* A lot of this stuff is pretty hard to test without a very elaborate
  harness, but I added a unit test for the most complicated part (though it
  requires LocalSystem to run).

Updates https://github.com/tailscale/corp/issues/13998

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2023-11-30 14:04:27 -08:00
Adrian Dewhurst
1ef5bd5381 util/osdiag, util/winutil: expose Windows policy key
The Windows base registry key is already exported but the policy key was
not. util/osdiag currently replicates the string rather than the
preferred approach of reusing the constant.

Updates #cleanup

Change-Id: I6c1c45337896c744059b85643da2364fb3f232f2
Signed-off-by: Adrian Dewhurst <adrian@tailscale.com>
2023-11-15 15:01:25 -05:00
Aaron Klotz
855f79fad7 cmd/tailscaled, util/winutil: changes to process and token APIs in winutil
This PR changes the internal getTokenInfo function to use generics.
I also removed our own implementations for obtaining a token's user
and primary group in favour of calling the ones now available in
x/sys/windows.

Furthermore, I added two new functions for working with tokens, logon
session IDs, and Terminal Services / RDP session IDs.

I modified our privilege enabling code to allow enabling of multiple
privileges via one single function call.

Finally, I added the ProcessImageName function and updated the code in
tailscaled_windows.go to use that instead of directly calling the
underlying API.

All of these changes will be utilized by subsequent PRs pertaining to
this issue.

Updates https://github.com/tailscale/corp/issues/13998

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2023-11-15 12:07:19 -07:00
Andrew Lytvynov
aba4bd0c62
util/winutil: simplify dropping privileges after use (#10099)
To safely request and drop privileges, runtime.Lock/UnlockOSThread and
windows.Impersonate/RevertToSelf should be called. Add these calls to
winutil.EnableCurrentThreadPrivilege so that callers don't need to worry
about it.

Updates https://github.com/tailscale/corp/issues/15488

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>
2023-11-06 11:37:37 -08:00
Aaron Klotz
fbc18410ad ipn/ipnauth: improve the Windows token administrator check
(*Token).IsAdministrator is supposed to return true even when the user is
running with a UAC limited token. The idea is that, for the purposes of
this check, we don't care whether the user is *currently* running with
full Admin rights, we just want to know whether the user can
*potentially* do so.

We accomplish this by querying for the token's "linked token," which
should be the fully-elevated variant, and checking its group memberships.

We also switch ipn/ipnserver/(*Server).connIsLocalAdmin to use the elevation
check to preserve those semantics for tailscale serve; I want the
IsAdministrator check to be used for less sensitive things like toggling
auto-update on and off.

Fixes #10036

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2023-11-03 14:37:04 -06:00
Claire Wang
e3d6236606
winutil: refactor methods to get values from registry to also return (#9536)
errors
Updates tailscale/corp#14879

Signed-off-by: Claire Wang <claire@tailscale.com>
2023-09-26 13:15:11 -04:00
Brad Fitzpatrick
dc7aa98b76 all: use set.Set consistently instead of map[T]struct{}
I didn't clean up the more idiomatic map[T]bool with true values, at
least yet.  I just converted the relatively awkward struct{}-valued
maps.

Updates #cleanup

Change-Id: I758abebd2bb1f64bc7a9d0f25c32298f4679c14f
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
2023-09-09 10:59:19 -07:00
Aaron Klotz
ea693eacb6 util/winutil: add RegisterForRestart, allowing programs to indicate their preferences to the Windows restart manager
In order for the installer to restart the GUI correctly post-upgrade, we
need the GUI to be able to register its restart preferences.

This PR adds API support for doing so. I'm adding it to OSS so that it
is available should we need to do any such registrations on OSS binaries
in the future.

Updates https://github.com/tailscale/corp/issues/13998

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2023-08-22 15:06:48 -06:00
Aaron Klotz
b07347640c util/winutil/authenticode: add missing docs for CertSubjectError
A #cleanup PR.

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2023-08-14 11:07:12 -06:00
Aaron Klotz
3d2e35c053 util/winutil/authenticode: fix an inaccurate doc comment
A #cleanup PR

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2023-08-09 15:33:49 -06:00
Aaron Klotz
37925b3e7a go.mod, cmd/tailscaled, ipn/localapi, util/osdiag, util/winutil, util/winutil/authenticode: add Windows module list to OS-specific logs that are written upon bugreport
* We update wingoes to pick up new version information functionality
  (See pe/version.go in the https://github.com/dblohm7/wingoes repo);
* We move the existing LogSupportInfo code (including necessary syscall
  stubs) out of util/winutil into a new package, util/osdiag, and implement
  the public LogSupportInfo function may be implemented for other platforms
  as needed;
* We add a new reason argument to LogSupportInfo and wire that into
  localapi's bugreport implementation;
* We add module information to the Windows implementation of LogSupportInfo
  when reason indicates a bugreport. We enumerate all loaded modules in our
  process, and for each one we gather debug, authenticode signature, and
  version information.

Fixes #7802

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2023-08-03 11:33:14 -06:00
Aaron Klotz
7adf15f90e cmd/tailscale/cli, util/winutil/authenticode: flesh out authenticode support
Previously, tailscale upgrade was doing the bare minimum for checking
authenticode signatures via `WinVerifyTrustEx`. This is fine, but we can do
better:

* WinVerifyTrustEx verifies that the binary's signature is valid, but it doesn't
  determine *whose* signature is valid; tailscale upgrade should also ensure that
  the binary is actually signed *by us*.
* I added the ability to check the signatures of MSI files.
* In future PRs I will be adding diagnostic logging that lists details about
  every module (ie, DLL) loaded into our process. As part of that metadata, I
  want to be able to extract information about who signed the binaries.

This code is modelled on some C++ I wrote for Firefox back in the day. See
https://searchfox.org/mozilla-central/rev/27e4816536c891d85d63695025f2549fd7976392/toolkit/xre/dllservices/mozglue/Authenticode.cpp
for reference.

Fixes #8284

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2023-08-01 14:27:30 -06:00
Aaron Klotz
2aa8299c37 cmd/tailscaled, util/winutil: log our registry keys during tailscaled startup
In order to improve our ability to understand the state of policies and
registry settings when troubleshooting, we enumerate all values in all subkeys.
x/sys/windows does not already offer this, so we need to call RegEnumValue
directly.

For now we're just logging this during startup, however in a future PR I plan to
also trigger this code during a bugreport. I also want to log more than just
registry.

Fixes #8141

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2023-06-01 13:39:17 -06:00
Andrew Dunham
280255acae
various: add golangci-lint, fix issues (#7905)
This adds an initial and intentionally minimal configuration for
golang-ci, fixes the issues reported, and adds a GitHub Action to check
new pull requests against this linter configuration.

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I8f38fbc315836a19a094d0d3e986758b9313f163
2023-04-17 18:38:24 -04:00
Aaron Klotz
90fd04cbde ipn/ipnlocal, util/winutil/policy: modify Windows profile migration to load legacy prefs from within tailscaled
I realized that a lot of the problems that we're seeing around migration and
LocalBackend state can be avoided if we drive Windows pref migration entirely
from within tailscaled. By doing it this way, tailscaled can automatically
perform the migration as soon as the connection with the client frontend is
established.

Since tailscaled is already running as LocalSystem, it already has access to
the user's local AppData directory. The profile manager already knows which
user is connected, so we simply need to resolve the user's prefs file and read
it from there.

Of course, to properly migrate this information we need to also check system
policies. I moved a bunch of policy resolution code out of the GUI and into
a new package in util/winutil/policy.

Updates #7626

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2023-04-03 14:41:46 -07:00
Will Norris
71029cea2d all: update copyright and license headers
This updates all source files to use a new standard header for copyright
and license declaration.  Notably, copyright no longer includes a date,
and we now use the standard SPDX-License-Identifier header.

This commit was done almost entirely mechanically with perl, and then
some minimal manual fixes.

Updates #6865

Signed-off-by: Will Norris <will@tailscale.com>
2023-01-27 15:36:29 -08:00
Brad Fitzpatrick
d9144c73a8 cmd/tailscale: add start of "tailscale update" command
Goal: one way for users to update Tailscale, downgrade, switch tracks,
regardless of platform (Windows, most Linux distros, macOS, Synology).

This is a start.

Updates #755, etc

Change-Id: I23466da1ba41b45f0029ca79a17f5796c2eedd92
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
2023-01-14 07:53:41 -08:00
Aaron Klotz
3c452b9880 util/winutil: fix erroneous condition in implementation of getRegIntegerInternal
We only want to log when err != registry.ErrNotExist. The condition was backward.

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2022-12-19 15:12:53 -06:00
Aaron Klotz
6e33d2da2b ipn/ipnauth, util/winutil: add temporary LookupPseudoUser workaround to address os/user.LookupId errors on Windows
I added util/winutil/LookupPseudoUser, which essentially consists of the bits
that I am in the process of adding to Go's standard library.

We check the provided SID for "S-1-5-x" where 17 <= x <= 20 (which are the
known pseudo-users) and then manually populate a os/user.User struct with
the correct information.

Fixes https://github.com/tailscale/tailscale/issues/869
Fixes https://github.com/tailscale/tailscale/issues/2894

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2022-11-28 15:53:34 -06:00
Brad Fitzpatrick
da8def8e13 all: remove old +build tags
The //go:build syntax was introduced in Go 1.17:

https://go.dev/doc/go1.17#build-lines

gofmt has kept the +build and go:build lines in sync since
then, but enough time has passed. Time to remove them.

Done with:

    perl -i -npe 's,^// \+build.*\n,,' $(git grep -l -F '+build')

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
2022-11-04 07:25:42 -07:00
Adrian Dewhurst
c3a5489e72 util/winutil: remove log spam for missing registry keys
It's normal for HKLM\SOFTWARE\Policies\Tailscale to not exist but that
currently produces a lot of log spam.

Signed-off-by: Adrian Dewhurst <adrian@tailscale.com>
2022-11-03 18:55:39 -04:00
Aaron Klotz
44f13d32d7 cmd/tailscaled, util/winutil: log Windows service diagnostics when the wintun device fails to install
I added new functions to winutil to obtain the state of a service and all
its depedencies, serialize them to JSON, and write them to a Logf.

When tstun.New returns a wrapped ERROR_DEVICE_NOT_AVAILABLE, we know that wintun
installation failed. We then log the service graph rooted at "NetSetupSvc".
We are interested in that specific service because network devices will not
install if that service is not running.

Updates https://github.com/tailscale/tailscale/issues/5531

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2022-09-28 16:09:10 -06:00
Maisem Ali
545639ee44 util/winutil: consolidate interface specific registry keys
Code movement to allow reuse in a follow up PR.

Updates #1659

Signed-off-by: Maisem Ali <maisem@tailscale.com>
2022-08-14 22:34:59 -07:00
Aaron Klotz
b005b79236 net/dns, paths, util/winutil: change net/dns/windowsManager NRPT management to support more than 50 domains.
AFAICT this isn't documented on MSDN, but based on the issue referenced below,
NRPT rules are not working when a rule specifies > 50 domains.

This patch modifies our NRPT rule generator to split the list of domains
into chunks as necessary, and write a separate rule for each chunk.

For compatibility reasons, we continue to use the hard-coded rule ID, but
as additional rules are required, we generate new GUIDs. Those GUIDs are
stored under the Tailscale registry path so that we know which rules are ours.

I made some changes to winutils to add additional helper functions in support
of both the code and its test: I added additional registry accessors, and also
moved some token accessors from paths to util/winutil.

Fixes https://github.com/tailscale/coral/issues/63

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2022-05-27 14:56:09 -06:00
Aaron Klotz
c163b2a3f1 util/winutil, util/winutil/vss: remove winrestore and vss as they are unnecessary.
I wrote this code way back at the beginning of my tenure at Tailscale when we
had concerns about needing to restore deleted machine keys from backups.

We never ended up using this functionality, and the code is now getting in the
way, so we might as well remove it.

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2022-05-26 12:13:36 -06:00
Aaron Klotz
82cd98609f util/winutil: migrate corp's winutil into OSS.
It makes the most sense to have all our utility functions reside in one place.
There was nothing in corp that could not reasonably live in OSS.

I also updated `StartProcessAsChild` to no longer depend on `futureexec`,
thus reducing the amount of code that needed migration. I tested this change
with `tswin` and it is working correctly.

I have a follow-up PR to remove the corresponding code from corp.

The migrated code was mostly written by @alexbrainman.
Sourced from corp revision 03e90cfcc4dd7b8bc9b25eb13a26ec3a24ae0ef9

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2022-02-10 15:22:55 -07:00
Aaron Klotz
3a74f2d2d7 cmd/tailscaled, util/winutil: add accessor functions for Windows system policies.
This patch adds new functions to be used when accessing system policies,
and revises callers to use the new functions. They first attempt the new
registry path for policies, and if that fails, attempt to fall back to the
legacy path.

We keep non-policy variants of these functions because we should be able to
retain the ability to read settings from locations that are not exposed to
sysadmins for group policy edits.

The remaining changes will be done in corp.

Updates https://github.com/tailscale/tailscale/issues/3584

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2022-02-09 14:58:51 -07:00
Brad Fitzpatrick
0626cf4183 util/winutil: fix build
It was broken on Windows:

Error: util\winutil\winutil_windows.go:15:7: regBase redeclared in this block
Error:                                       D:\a\tailscale\tailscale\util\winutil\winutil_notwindows.go:7:17: previous declaration
Error: util\winutil\winutil_windows.go:29:6: getRegString redeclared in this block
Error:                                       D:\a\tailscale\tailscale\util\winutil\winutil_notwindows.go:9:40: previous declaration
Error: util\winutil\winutil_windows.go:47:6: getRegInteger redeclared in this block
Error:                                       D:\a\tailscale\tailscale\util\winutil\winutil_notwindows.go:11:48: previous declaration
Error: util\winutil\winutil_windows.go:77:6: isSIDValidPrincipal redeclared in this block
Error:                                       D:\a\tailscale\tailscale\util\winutil\winutil_notwindows.go:13:38: previous declaration

Change-Id: Ib1ce4b647f5711547840c736b933a6c42bf09583
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
2022-02-02 16:45:29 -08:00
Aaron Klotz
d7962e3bcf ipn/ipnserver, util/winutil: update workaround for os/user.LookupId failures on Windows to reject SIDs from deleted/invalid security principals.
Our current workaround made the user check too lax, thus allowing deleted
users. This patch adds a helper function to winutil that checks that the
uid's SID represents a valid Windows security principal.

Now if `lookupUserFromID` determines that the SID is invalid, we simply
propagate the error.

Updates https://github.com/tailscale/tailscale/issues/869

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2022-02-02 15:01:28 -07:00
Aaron Klotz
c6ea282b3f utils/winutil utils/winutil/vss: add utility function for extracting data from Windows System Restore Point backups.
utils/winutil/vss contains just enough COM wrapping to query the Volume Shadow Copy service for snapshots.
WalkSnapshotsForLegacyStateDir is the friendlier interface that adds awareness of our actual use case,
mapping the snapshots and locating our legacy state directory.

Updates #3011

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2021-10-18 15:48:42 -06:00
Aaron Klotz
3386a86fe5 util/winutil: add GetRegInteger
This helper allows us to retrieve `DWORD` and `QWORD` values from the Tailscale key in the Windows registry.

Signed-off-by: Aaron Klotz <aaron@tailscale.com>
2021-09-29 09:43:22 -06:00
Josh Bleecher Snyder
a5da4ed981 all: gofmt with Go 1.17
This adds "//go:build" lines and tidies up existing "// +build" lines.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
2021-08-05 15:54:00 -07:00
David Crawshaw
6b9f8208f4 net/dns: do not run wsl.exe as LocalSystem
It doesn't work. It needs to run as the user.

	https://github.com/microsoft/WSL/issues/4803

The mechanism for doing this was extracted from:

	https://web.archive.org/web/20101009012531/http://blogs.msdn.com/b/winsdk/archive/2009/07/14/launching-an-interactive-process-from-windows-service-in-windows-vista-and-later.aspx

While here, we also reclaculate WSL distro set on SetDNS.
This accounts for:

	1. potential inability to access wsl.exe on startup
	2. WSL being installed while Tailscale is running
	3. A new WSL distrobution being installed

Signed-off-by: David Crawshaw <crawshaw@tailscale.com>
2021-06-30 10:11:33 -07:00
Christine Dodrill
a480b1baa5
logpolicy: set log target on windows based on a registry key (#1542)
Signed-off-by: Christine Dodrill <xe@tailscale.com>
2021-03-18 13:23:56 -04:00
Brad Fitzpatrick
2d5db90161 util/winutil: make it actually compile
Helps to use the right GOOS after refactoring, sigh.

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
2021-02-26 20:52:23 -08:00
Brad Fitzpatrick
e98cdbb8b6 util/winutil: add little Windows utility package
Code from Alex Brainman, split out of another change. I changed it to
a comma-ok return and tweaked the docs a bit.
2021-02-26 20:42:00 -08:00