elevate: do not show UAC prompt for frictionless UX

5 files changed, 297 insertions, 1 deletions

diff --git a/elevate/mksyscall.go b/elevate/mksyscall.go
new file mode 100644
index 00000000..fda63f27
--- /dev/null
+++ b/elevate/mksyscall.go
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2019 WireGuard LLC. All Rights Reserved.
+ */
+
+package elevate
+
+//go:generate go run $GOROOT/src/syscall/mksyscall_windows.go -output zsyscall_windows.go syscall_windows.go
diff --git a/elevate/shellexecute.go b/elevate/shellexecute.go
new file mode 100644
index 00000000..c3dc84eb
--- /dev/null
+++ b/elevate/shellexecute.go
@@ -0,0 +1,126 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2019 WireGuard LLC. All Rights Reserved.
+ */
+
+package elevate
+
+import (
+	"path/filepath"
+	"runtime"
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+	"golang.org/x/sys/windows/registry"
+)
+
+const (
+	releaseOffset      = 2
+	shellExecuteOffset = 9
+
+	cSEE_MASK_DEFAULT = 0
+)
+
+func ShellExecute(program string, arguments string, directory string, show int32) (err error) {
+	var (
+		program16   *uint16
+		arguments16 *uint16
+		directory16 *uint16
+	)
+
+	if len(program) > 0 {
+		program16, _ = windows.UTF16PtrFromString(program)
+	}
+	if len(arguments) > 0 {
+		arguments16, _ = windows.UTF16PtrFromString(arguments)
+	}
+	if len(directory) > 0 {
+		directory16, _ = windows.UTF16PtrFromString(directory)
+	}
+
+	defer func() {
+		if err != nil {
+			err = windows.ShellExecute(0, windows.StringToUTF16Ptr("runas"), program16, arguments16, directory16, show)
+		}
+	}()
+
+	processToken, err := windows.OpenCurrentProcessToken()
+	if err != nil {
+		return
+	}
+	defer processToken.Close()
+	if processToken.IsElevated() {
+		err = windows.ERROR_SUCCESS
+		return
+	}
+
+	key, err := registry.OpenKey(registry.LOCAL_MACHINE, "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\UAC\\COMAutoApprovalList", registry.QUERY_VALUE)
+	if err == nil {
+		var autoApproved uint64
+		autoApproved, _, err = key.GetIntegerValue("{3E5FC7F9-9A51-4367-9063-A120244FBEC7}")
+		key.Close()
+		if err != nil {
+			return
+		}
+		if uint32(autoApproved) == 0 {
+			err = windows.ERROR_ACCESS_DENIED
+			return
+		}
+	}
+
+	moduleHandle, err := getModuleHandle(nil)
+	if err != nil {
+		return
+	}
+	var dataTableEntry *cLDR_DATA_TABLE_ENTRY
+	if ret := ldrFindEntryForAddress(moduleHandle, &dataTableEntry); ret != 0 {
+		err = syscall.Errno(windows.ERROR_INTERNAL_ERROR)
+		return
+	}
+	var windowsDirectory [windows.MAX_PATH]uint16
+	if _, err = getWindowsDirectory(&windowsDirectory[0], windows.MAX_PATH); err != nil {
+		return
+	}
+	originalPath := dataTableEntry.FullDllName.Buffer
+	explorerPath := windows.StringToUTF16Ptr(filepath.Join(windows.UTF16ToString(windowsDirectory[:]), "explorer.exe"))
+	rtlInitUnicodeString(&dataTableEntry.FullDllName, explorerPath)
+	defer func() {
+		rtlInitUnicodeString(&dataTableEntry.FullDllName, originalPath)
+		runtime.KeepAlive(explorerPath)
+	}()
+
+	if err = coInitializeEx(0, cCOINIT_APARTMENTTHREADED); err == nil {
+		defer coUninitialize()
+	}
+
+	var interfacePointer **[0xffff]uintptr
+	if err = coGetObject(
+		windows.StringToUTF16Ptr("Elevation:Administrator!new:{3E5FC7F9-9A51-4367-9063-A120244FBEC7}"),
+		&cBIND_OPTS3{
+			cbStruct:       uint32(unsafe.Sizeof(cBIND_OPTS3{})),
+			dwClassContext: cCLSCTX_LOCAL_SERVER,
+		},
+		&windows.GUID{0x6EDD6D74, 0xC007, 0x4E75, [8]byte{0xB7, 0x6A, 0xE5, 0x74, 0x09, 0x95, 0xE2, 0x4C}},
+		&interfacePointer,
+	); err != nil {
+		return
+	}
+
+	defer syscall.Syscall((*interfacePointer)[releaseOffset], 1, uintptr(unsafe.Pointer(interfacePointer)), 0, 0)
+
+	if ret, _, _ := syscall.Syscall6((*interfacePointer)[shellExecuteOffset], 6,
+		uintptr(unsafe.Pointer(interfacePointer)),
+		uintptr(unsafe.Pointer(program16)),
+		uintptr(unsafe.Pointer(arguments16)),
+		uintptr(unsafe.Pointer(directory16)),
+		cSEE_MASK_DEFAULT,
+		uintptr(show),
+	); ret != uintptr(windows.ERROR_SUCCESS) {
+		err = syscall.Errno(ret)
+		return
+	}
+
+	err = nil
+	return
+}
diff --git a/elevate/syscall_windows.go b/elevate/syscall_windows.go
new file mode 100644
index 00000000..c73be812
--- /dev/null
+++ b/elevate/syscall_windows.go
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2019 WireGuard LLC. All Rights Reserved.
+ */
+
+package elevate
+
+type cBIND_OPTS3 struct {
+	cbStruct            uint32
+	grfFlags            uint32
+	grfMode             uint32
+	dwTickCountDeadline uint32
+	dwTrackFlags        uint32
+	dwClassContext      uint32
+	locale              uint32
+	pServerInfo         *uintptr
+	hwnd                *uintptr
+}
+
+type cUNICODE_STRING struct {
+	Length        uint16
+	MaximumLength uint16
+	Buffer        *uint16
+}
+
+type cLDR_DATA_TABLE_ENTRY struct {
+	Reserved1          [2]uintptr
+	InMemoryOrderLinks [2]uintptr
+	Reserved2          [2]uintptr
+	DllBase            uintptr
+	Reserved3          [2]uintptr
+	FullDllName        cUNICODE_STRING
+	Reserved4          [8]byte
+	Reserved5          [3]uintptr
+	Reserved6          uintptr
+	TimeDateStamp      uint32
+}
+
+const (
+	cCLSCTX_LOCAL_SERVER      = 4
+	cCOINIT_APARTMENTTHREADED = 2
+)
+
+//sys	getModuleHandle(moduleName *uint16) (moduleHandle uintptr, err error) [failretval==0] = kernel32.GetModuleHandleW
+//sys	getWindowsDirectory(windowsDirectory *uint16, inLen uint32) (outLen uint32, err error) [failretval==0] = kernel32.GetWindowsDirectoryW
+
+//sys	rtlInitUnicodeString(destinationString *cUNICODE_STRING, sourceString *uint16) = ntdll.RtlInitUnicodeString
+//sys	ldrFindEntryForAddress(moduleHandle uintptr, entry **cLDR_DATA_TABLE_ENTRY) (ntstatus uint32) = ntdll.LdrFindEntryForAddress
+
+//sys	coInitializeEx(reserved uintptr, coInit uint32) (ret error) = ole32.CoInitializeEx
+//sys	coUninitialize() = ole32.CoUninitialize
+//sys	coGetObject(name *uint16, bindOpts *cBIND_OPTS3, guid *windows.GUID, functionTable ***[0xffff]uintptr) (ret error) = ole32.CoGetObject
diff --git a/elevate/zsyscall_windows.go b/elevate/zsyscall_windows.go
new file mode 100644
index 00000000..b16b5f5d
--- /dev/null
+++ b/elevate/zsyscall_windows.go
@@ -0,0 +1,109 @@
+// Code generated by 'go generate'; DO NOT EDIT.
+
+package elevate
+
+import (
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+var _ unsafe.Pointer
+
+// Do the interface allocations only once for common
+// Errno values.
+const (
+	errnoERROR_IO_PENDING = 997
+)
+
+var (
+	errERROR_IO_PENDING error = syscall.Errno(errnoERROR_IO_PENDING)
+)
+
+// errnoErr returns common boxed Errno values, to prevent
+// allocations at runtime.
+func errnoErr(e syscall.Errno) error {
+	switch e {
+	case 0:
+		return nil
+	case errnoERROR_IO_PENDING:
+		return errERROR_IO_PENDING
+	}
+	// TODO: add more here, after collecting data on the common
+	// error values see on Windows. (perhaps when running
+	// all.bat?)
+	return e
+}
+
+var (
+	modkernel32 = windows.NewLazySystemDLL("kernel32.dll")
+	modntdll    = windows.NewLazySystemDLL("ntdll.dll")
+	modole32    = windows.NewLazySystemDLL("ole32.dll")
+
+	procGetModuleHandleW       = modkernel32.NewProc("GetModuleHandleW")
+	procGetWindowsDirectoryW   = modkernel32.NewProc("GetWindowsDirectoryW")
+	procRtlInitUnicodeString   = modntdll.NewProc("RtlInitUnicodeString")
+	procLdrFindEntryForAddress = modntdll.NewProc("LdrFindEntryForAddress")
+	procCoInitializeEx         = modole32.NewProc("CoInitializeEx")
+	procCoUninitialize         = modole32.NewProc("CoUninitialize")
+	procCoGetObject            = modole32.NewProc("CoGetObject")
+)
+
+func getModuleHandle(moduleName *uint16) (moduleHandle uintptr, err error) {
+	r0, _, e1 := syscall.Syscall(procGetModuleHandleW.Addr(), 1, uintptr(unsafe.Pointer(moduleName)), 0, 0)
+	moduleHandle = uintptr(r0)
+	if moduleHandle == 0 {
+		if e1 != 0 {
+			err = errnoErr(e1)
+		} else {
+			err = syscall.EINVAL
+		}
+	}
+	return
+}
+
+func getWindowsDirectory(windowsDirectory *uint16, inLen uint32) (outLen uint32, err error) {
+	r0, _, e1 := syscall.Syscall(procGetWindowsDirectoryW.Addr(), 2, uintptr(unsafe.Pointer(windowsDirectory)), uintptr(inLen), 0)
+	outLen = uint32(r0)
+	if outLen == 0 {
+		if e1 != 0 {
+			err = errnoErr(e1)
+		} else {
+			err = syscall.EINVAL
+		}
+	}
+	return
+}
+
+func rtlInitUnicodeString(destinationString *cUNICODE_STRING, sourceString *uint16) {
+	syscall.Syscall(procRtlInitUnicodeString.Addr(), 2, uintptr(unsafe.Pointer(destinationString)), uintptr(unsafe.Pointer(sourceString)), 0)
+	return
+}
+
+func ldrFindEntryForAddress(moduleHandle uintptr, entry **cLDR_DATA_TABLE_ENTRY) (ntstatus uint32) {
+	r0, _, _ := syscall.Syscall(procLdrFindEntryForAddress.Addr(), 2, uintptr(moduleHandle), uintptr(unsafe.Pointer(entry)), 0)
+	ntstatus = uint32(r0)
+	return
+}
+
+func coInitializeEx(reserved uintptr, coInit uint32) (ret error) {
+	r0, _, _ := syscall.Syscall(procCoInitializeEx.Addr(), 2, uintptr(reserved), uintptr(coInit), 0)
+	if r0 != 0 {
+		ret = syscall.Errno(r0)
+	}
+	return
+}
+
+func coUninitialize() {
+	syscall.Syscall(procCoUninitialize.Addr(), 0, 0, 0, 0)
+	return
+}
+
+func coGetObject(name *uint16, bindOpts *cBIND_OPTS3, guid *windows.GUID, functionTable ***[0xffff]uintptr) (ret error) {
+	r0, _, _ := syscall.Syscall6(procCoGetObject.Addr(), 4, uintptr(unsafe.Pointer(name)), uintptr(unsafe.Pointer(bindOpts)), uintptr(unsafe.Pointer(guid)), uintptr(unsafe.Pointer(functionTable)), 0, 0)
+	if r0 != 0 {
+		ret = syscall.Errno(r0)
+	}
+	return
+}
diff --git a/main.go b/main.go
index 348f1df4..813663a5 100644
--- a/main.go
+++ b/main.go
@@ -15,6 +15,7 @@ import (
 	"golang.org/x/sys/windows"
 	"golang.zx2c4.com/wireguard/tun/wintun"
 
+	"golang.zx2c4.com/wireguard/windows/elevate"
 	"golang.zx2c4.com/wireguard/windows/manager"
 	"golang.zx2c4.com/wireguard/windows/ringlogger"
 	"golang.zx2c4.com/wireguard/windows/services"
@@ -84,7 +85,7 @@ func execElevatedManagerServiceInstaller() error {
 	if err != nil {
 		return err
 	}
-	err = windows.ShellExecute(0, windows.StringToUTF16Ptr("runas"), windows.StringToUTF16Ptr(path), windows.StringToUTF16Ptr("/installmanagerservice"), nil, windows.SW_SHOW)
+	err = elevate.ShellExecute(path, "/installmanagerservice", "", windows.SW_SHOW)
 	if err != nil {
 		return err
 	}