From c449929fefde11e5ff8ff5308f0db29b8132dee4 Mon Sep 17 00:00:00 2001
From: Eric Kohl <eric.kohl@reactos.org>
Date: Sat, 3 Apr 2021 09:38:07 +0200
Subject: [PATCH] [NTOS:EX] Use RtlCutoverTimeToSystemTime to determine the
 current time zone id

CORE-14658
---
 ntoskrnl/ex/time.c         | 77 ++++++++++++++++++++++++++++++++------
 sdk/include/ndk/rtlfuncs.h |  9 +++++
 2 files changed, 75 insertions(+), 11 deletions(-)

diff --git a/ntoskrnl/ex/time.c b/ntoskrnl/ex/time.c
index 44ce39d9ad9..ad971773a8d 100644
--- a/ntoskrnl/ex/time.c
+++ b/ntoskrnl/ex/time.c
@@ -225,6 +225,8 @@ BOOLEAN
 NTAPI
 ExRefreshTimeZoneInformation(IN PLARGE_INTEGER CurrentBootTime)
 {
+    LARGE_INTEGER StandardTime;
+    LARGE_INTEGER DaylightTime;
     LARGE_INTEGER CurrentTime;
     NTSTATUS Status;
 
@@ -232,20 +234,73 @@ ExRefreshTimeZoneInformation(IN PLARGE_INTEGER CurrentBootTime)
     Status = RtlQueryTimeZoneInformation(&ExpTimeZoneInfo);
     if (!NT_SUCCESS(Status))
     {
-        /* Failed, clear all data */
-        RtlZeroMemory(&ExpTimeZoneInfo, sizeof(RTL_TIME_ZONE_INFORMATION));
-        ExpTimeZoneBias.QuadPart = (LONGLONG)0;
-        ExpTimeZoneId = TIME_ZONE_ID_UNKNOWN;
+        DPRINT1("RtlQueryTimeZoneInformation() failed (Status 0x%08lx)\n", Status);
+        return FALSE;
+    }
+
+    /* Get the default bias */
+    ExpTimeZoneBias.QuadPart = (LONGLONG)ExpTimeZoneInfo.Bias * TICKSPERMINUTE;
+
+    if (ExpTimeZoneInfo.StandardDate.Month != 0 &&
+        ExpTimeZoneInfo.DaylightDate.Month != 0)
+    {
+        /* Get this years standard start time */
+        if (!RtlCutoverTimeToSystemTime(&ExpTimeZoneInfo.StandardDate,
+                                        &StandardTime,
+                                        CurrentBootTime,
+                                        TRUE))
+        {
+            DPRINT1("RtlCutoverTimeToSystemTime() for StandardDate failed!\n");
+            return FALSE;
+        }
+
+        /* Get this years daylight start time */
+        if (!RtlCutoverTimeToSystemTime(&ExpTimeZoneInfo.DaylightDate,
+                                        &DaylightTime,
+                                        CurrentBootTime,
+                                        TRUE))
+        {
+            DPRINT1("RtlCutoverTimeToSystemTime() for DaylightDate failed!\n");
+            return FALSE;
+        }
+
+        /* Determine the time zone id and update the time zone bias */
+        if (DaylightTime.QuadPart < StandardTime.QuadPart)
+        {
+            if ((CurrentBootTime->QuadPart >= DaylightTime.QuadPart) &&
+                (CurrentBootTime->QuadPart < StandardTime.QuadPart))
+            {
+                DPRINT("Daylight time!\n");
+                ExpTimeZoneId = TIME_ZONE_ID_DAYLIGHT;
+                ExpTimeZoneBias.QuadPart += (LONGLONG)ExpTimeZoneInfo.DaylightBias * TICKSPERMINUTE;
+            }
+            else
+            {
+                DPRINT("Standard time!\n");
+                ExpTimeZoneId = TIME_ZONE_ID_STANDARD;
+                ExpTimeZoneBias.QuadPart += (LONGLONG)ExpTimeZoneInfo.StandardBias * TICKSPERMINUTE;
+            }
+        }
+        else
+        {
+            if ((CurrentBootTime->QuadPart >= StandardTime.QuadPart) &&
+                (CurrentBootTime->QuadPart < DaylightTime.QuadPart))
+            {
+                DPRINT("Standard time!\n");
+                ExpTimeZoneId = TIME_ZONE_ID_STANDARD;
+                ExpTimeZoneBias.QuadPart += (LONGLONG)ExpTimeZoneInfo.StandardBias * TICKSPERMINUTE;
+            }
+            else
+            {
+                DPRINT("Daylight time!\n");
+                ExpTimeZoneId = TIME_ZONE_ID_DAYLIGHT;
+                ExpTimeZoneBias.QuadPart += (LONGLONG)ExpTimeZoneInfo.DaylightBias * TICKSPERMINUTE;
+            }
+        }
     }
     else
     {
-        /* FIXME: Calculate transition dates */
-
-        /* Set bias and ID */
-        ExpTimeZoneBias.QuadPart = ((LONGLONG)(ExpTimeZoneInfo.Bias +
-            ExpTimeZoneInfo.StandardBias)) *
-            TICKSPERMINUTE;
-        ExpTimeZoneId = TIME_ZONE_ID_STANDARD;
+        ExpTimeZoneId = TIME_ZONE_ID_UNKNOWN;
     }
 
     /* Change it for user-mode applications */
diff --git a/sdk/include/ndk/rtlfuncs.h b/sdk/include/ndk/rtlfuncs.h
index 7817278a17f..513fc195b5f 100644
--- a/sdk/include/ndk/rtlfuncs.h
+++ b/sdk/include/ndk/rtlfuncs.h
@@ -4533,6 +4533,15 @@ RtlIpv6StringToAddressExW(
 //
 // Time Functions
 //
+NTSYSAPI
+BOOLEAN
+NTAPI
+RtlCutoverTimeToSystemTime(
+    _In_ PTIME_FIELDS CutoverTimeFields,
+    _Out_ PLARGE_INTEGER SystemTime,
+    _In_ PLARGE_INTEGER CurrentTime,
+    _In_ BOOLEAN ThisYearsCutoverOnly);
+
 NTSYSAPI
 NTSTATUS
 NTAPI