windows: replace all StringToUTF16 calls with UTF16FromString

`StringToUTF16` is deprecated and will panic if given an "invalid"
string (in particular, one that has a null byte in it).  The replacement
function is `UTF16FromString`, and it returns an error if there was
a problem.

This change replaces all uses of `StringToUTF16` with `UTF16FromString`.
The `service` struct now no longer stores a `string` name but rather
a `*uint16` pointer to the name.

It should not be possible to panic due to UTF16 string conversion
at this point.

Fixes golang/go#73006

Change-Id: Idce9cdbb4651fef8481f0cad19b5df0314fd4277
Reviewed-on: https://go-review.googlesource.com/c/sys/+/659936
Reviewed-by: Carlos Amedee <carlos@golang.org>
Auto-Submit: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

windows/svc/mgr/mgr.go

@@ -34,7 +34,11 @@ func Connect() (*Mgr, error) {
 func ConnectRemote(host string) (*Mgr, error) {
 	var s *uint16
 	if host != "" {
-		s = syscall.StringToUTF16Ptr(host)
+		var err error
+		s, err = syscall.UTF16PtrFromString(host)
+		if err != nil {
+			return nil, err
+		}
 	}
 	h, err := windows.OpenSCManager(s, nil, windows.SC_MANAGER_ALL_ACCESS)
 	if err != nil {
@@ -78,11 +82,11 @@ func (m *Mgr) LockStatus() (*LockStatus, error) {
 	}
 }
 
-func toPtr(s string) *uint16 {
+func toPtr(s string) (*uint16, error) {
 	if len(s) == 0 {
-		return nil
+		return nil, nil
 	}
-	return syscall.StringToUTF16Ptr(s)
+	return syscall.UTF16PtrFromString(s)
 }
 
 // toStringBlock terminates strings in ss with 0, and then
@@ -122,10 +126,34 @@ func (m *Mgr) CreateService(name, exepath string, c Config, args ...string) (*Se
 	for _, v := range args {
 		s += " " + syscall.EscapeArg(v)
 	}
-	h, err := windows.CreateService(m.Handle, toPtr(name), toPtr(c.DisplayName),
+	namePointer, err := toPtr(name)
+	if err != nil {
+		return nil, err
+	}
+	displayNamePointer, err := toPtr(c.DisplayName)
+	if err != nil {
+		return nil, err
+	}
+	sPointer, err := toPtr(s)
+	if err != nil {
+		return nil, err
+	}
+	loadOrderGroupPointer, err := toPtr(c.LoadOrderGroup)
+	if err != nil {
+		return nil, err
+	}
+	serviceStartNamePointer, err := toPtr(c.ServiceStartName)
+	if err != nil {
+		return nil, err
+	}
+	passwordPointer, err := toPtr(c.Password)
+	if err != nil {
+		return nil, err
+	}
+	h, err := windows.CreateService(m.Handle, namePointer, displayNamePointer,
 		windows.SERVICE_ALL_ACCESS, c.ServiceType,
-		c.StartType, c.ErrorControl, toPtr(s), toPtr(c.LoadOrderGroup),
-		nil, toStringBlock(c.Dependencies), toPtr(c.ServiceStartName), toPtr(c.Password))
+		c.StartType, c.ErrorControl, sPointer, loadOrderGroupPointer,
+		nil, toStringBlock(c.Dependencies), serviceStartNamePointer, passwordPointer)
 	if err != nil {
 		return nil, err
 	}
@@ -159,7 +187,12 @@ func (m *Mgr) CreateService(name, exepath string, c Config, args ...string) (*Se
 // OpenService retrieves access to service name, so it can
 // be interrogated and controlled.
 func (m *Mgr) OpenService(name string) (*Service, error) {
-	h, err := windows.OpenService(m.Handle, syscall.StringToUTF16Ptr(name), windows.SERVICE_ALL_ACCESS)
+	namePointer, err := syscall.UTF16PtrFromString(name)
+	if err != nil {
+		return nil, err
+	}
+
+	h, err := windows.OpenService(m.Handle, namePointer, windows.SERVICE_ALL_ACCESS)
 	if err != nil {
 		return nil, err
 	}