[WIN32SS:NTUSER] Update SetWindowStationUser() and NtUserSetWindowStationUser() prototypes.

Also, improve NtUserSetWindowStationUser() capture order, make psid optional as it should (and avoid a user-mode triggered BSOD), and initialize luidUser only when everything succeeded.

win32ss/include/ntuser.h

@@ -3289,10 +3289,10 @@ NtUserSetWindowsHookEx(
 BOOL
 NTAPI
 NtUserSetWindowStationUser(
-    HWINSTA hWindowStation,
+    IN HWINSTA hWindowStation,
-    PLUID pluid,
+    IN PLUID pluid,
-    PSID psid,
+    IN PSID psid OPTIONAL,
-    DWORD size);
+    IN DWORD size);
 
 WORD
 NTAPI

win32ss/user/ntuser/winsta.c

@@ -1482,16 +1482,18 @@ NtUserLockWorkStation(VOID)
     return ret;
 }
 
-BOOL APIENTRY
+BOOL
+NTAPI
 NtUserSetWindowStationUser(
-    HWINSTA hWindowStation,
+    IN HWINSTA hWindowStation,
-    PLUID pluid,
+    IN PLUID pluid,
-    PSID psid,
+    IN PSID psid OPTIONAL,
-    DWORD size)
+    IN DWORD size)
 {
+    BOOL Ret = FALSE;
     NTSTATUS Status;
     PWINSTATION_OBJECT WindowStation = NULL;
-    BOOL Ret = FALSE;
+    LUID luidUser;
 
     UserEnterExclusive();
 
@@ -1501,21 +1503,43 @@ NtUserSetWindowStationUser(
         goto Leave;
     }
 
+    /* Validate the window station */
     Status = IntValidateWindowStationHandle(hWindowStation,
                                             UserMode,
                                             0,
                                             &WindowStation,
-                                            0);
+                                            NULL);
     if (!NT_SUCCESS(Status))
     {
         goto Leave;
     }
 
+    /* Capture the user LUID */
+    _SEH2_TRY
+    {
+        ProbeForRead(pluid, sizeof(LUID), 1);
+        luidUser = *pluid;
+    }
+    _SEH2_EXCEPT(EXCEPTION_EXECUTE_HANDLER)
+    {
+        Status = _SEH2_GetExceptionCode();
+        _SEH2_YIELD(goto Leave);
+    }
+    _SEH2_END;
+
+    /* Reset the window station user LUID */
+    RtlZeroMemory(&WindowStation->luidUser, sizeof(LUID));
+
+    /* Reset the window station user SID */
     if (WindowStation->psidUser)
     {
         ExFreePoolWithTag(WindowStation->psidUser, USERTAG_SECURITY);
+        WindowStation->psidUser = NULL;
     }
 
+    /* Copy the new user SID if one has been provided */
+    if (psid)
+    {
         WindowStation->psidUser = ExAllocatePoolWithTag(PagedPool, size, USERTAG_SECURITY);
         if (WindowStation->psidUser == NULL)
         {
@@ -1523,13 +1547,11 @@ NtUserSetWindowStationUser(
             goto Leave;
         }
 
+        Status = STATUS_SUCCESS;
         _SEH2_TRY
         {
             ProbeForRead(psid, size, 1);
-        ProbeForRead(pluid, sizeof(LUID), 1);
-
             RtlCopyMemory(WindowStation->psidUser, psid, size);
-        WindowStation->luidUser = *pluid;
         }
         _SEH2_EXCEPT(EXCEPTION_EXECUTE_HANDLER)
         {
@@ -1543,11 +1565,17 @@ NtUserSetWindowStationUser(
             WindowStation->psidUser = NULL;
             goto Leave;
         }
+    }
+
+    /* Copy the new user LUID */
+    WindowStation->luidUser = luidUser;
 
     Ret = TRUE;
 
 Leave:
-    if (WindowStation) ObDereferenceObject(WindowStation);
+    if (WindowStation)
+        ObDereferenceObject(WindowStation);
+
     UserLeave();
     return Ret;
 }

win32ss/user/user32/misc/winsta.c

@@ -399,8 +399,8 @@ BOOL
 WINAPI
 SetWindowStationUser(
     IN HWINSTA hWindowStation,
-    IN PLUID pluid OPTIONAL,
+    IN PLUID pluid,
-    IN PSID psid,
+    IN PSID psid OPTIONAL,
     IN DWORD size)
 {
     BOOL Success;
@@ -410,7 +410,7 @@ SetWindowStationUser(
     {
         /* Signal log-on/off to WINSRV */
 
-        /* User is logging on if pluid != LuidNone, otherwise it is a log-off */
+        /* User is logging on if *pluid != LuidNone, otherwise it is a log-off */
         LUID LuidNone = {0, 0};
         BOOL IsLogon = (pluid && !RtlEqualLuid(pluid, &LuidNone));