From dbb6b0fe60e7ba224d17d11de351a0b0e3df149a Mon Sep 17 00:00:00 2001
From: basil00 <basil@reqrypt.org>
Date: Tue, 14 Nov 2017 20:20:18 +0800
Subject: [PATCH] Invert the checksum flags.

Zeroing the addr will default to full checksums.
---
 dll/windivert_helper.c |  6 +++---
 include/windivert.h    |  6 +++---
 sys/windivert.c        | 30 +++++++++++++++++++++---------
 3 files changed, 27 insertions(+), 15 deletions(-)

diff --git a/dll/windivert_helper.c b/dll/windivert_helper.c
index 0cff931..a8c6703 100644
--- a/dll/windivert_helper.c
+++ b/dll/windivert_helper.c
@@ -435,7 +435,7 @@ extern UINT WinDivertHelperCalcChecksums(PVOID pPacket, UINT packetLen,
     if (ip_header != NULL && !(flags & WINDIVERT_HELPER_NO_IP_CHECKSUM))
     {
         ip_header->Checksum = 0;
-        if (pAddr == NULL || pAddr->IPv4Checksum != 0)
+        if (pAddr == NULL || pAddr->PseudoIPChecksum == 0)
         {
             ip_header->Checksum = WinDivertHelperCalcChecksum(NULL, 0,
                 ip_header, ip_header->HdrLength*sizeof(UINT32));
@@ -478,7 +478,7 @@ extern UINT WinDivertHelperCalcChecksums(PVOID pPacket, UINT packetLen,
         {
             return count;
         }
-        if (pAddr == NULL || pAddr->TCPChecksum != 0)
+        if (pAddr == NULL || pAddr->PseudoTCPChecksum == 0)
         {
             // Full TCP checksum
             checksum_len = payload_len + tcp_header->HdrLength*sizeof(UINT32);
@@ -512,7 +512,7 @@ extern UINT WinDivertHelperCalcChecksums(PVOID pPacket, UINT packetLen,
         {
             return count;
         }
-        if (pAddr == NULL || pAddr->UDPChecksum != 0)
+        if (pAddr == NULL || pAddr->PseudoUDPChecksum == 0)
         {
             // Full UDP checksum
             checksum_len = payload_len + sizeof(WINDIVERT_UDPHDR);
diff --git a/include/windivert.h b/include/windivert.h
index 8bd80cd..4b4ed5e 100644
--- a/include/windivert.h
+++ b/include/windivert.h
@@ -63,9 +63,9 @@ typedef struct
     UINT8  Direction:1;                 /* Packet's direction. */
     UINT8  Loopback:1;                  /* Packet is loopback? */
     UINT8  Impostor:1;                  /* Packet is impostor? */
-    UINT8  IPv4Checksum:1;              /* Packet has full IPv4 checksum? */
-    UINT8  TCPChecksum:1;               /* Packet has full TCP checksum? */
-    UINT8  UDPChecksum:1;               /* Packet has full UDP checksum? */
+    UINT8  PseudoIPChecksum:1;          /* Packet has pseudo IPv4 checksum? */
+    UINT8  PseudoTCPChecksum:1;         /* Packet has pseudo TCP checksum? */
+    UINT8  PseudoUDPChecksum:1;         /* Packet has pseudo UDP checksum? */
     UINT8  Reserved:2;
 } WINDIVERT_ADDRESS, *PWINDIVERT_ADDRESS;
 
diff --git a/sys/windivert.c b/sys/windivert.c
index 553df73..8e8e007 100644
--- a/sys/windivert.c
+++ b/sys/windivert.c
@@ -1554,9 +1554,12 @@ static void windivert_read_service_request(packet_t packet,
         addr->Direction = direction;
         addr->Loopback = (loopback? 1: 0);
         addr->Impostor = (impostor? 1: 0);
-        addr->IPv4Checksum = ((checksums & WINDIVERT_IP_CHECKSUM) != 0? 1: 0);
-        addr->TCPChecksum = ((checksums & WINDIVERT_TCP_CHECKSUM) != 0? 1: 0);
-        addr->UDPChecksum = ((checksums & WINDIVERT_UDP_CHECKSUM) != 0? 1: 0);
+        addr->PseudoIPChecksum =
+            ((checksums & WINDIVERT_IP_CHECKSUM) == 0? 1: 0);
+        addr->PseudoTCPChecksum =
+            ((checksums & WINDIVERT_TCP_CHECKSUM) == 0? 1: 0);
+        addr->PseudoUDPChecksum =
+            ((checksums & WINDIVERT_UDP_CHECKSUM) == 0? 1: 0);
         addr->Reserved = 0;
     }
 
@@ -1763,24 +1766,33 @@ windivert_write_bad_packet:
         if (addr->Direction == WINDIVERT_DIRECTION_OUTBOUND)
         {
             checksums_info.Transmit.TcpChecksum =
-                (addr->TCPChecksum != 0? 0: 1);
+                (addr->PseudoTCPChecksum == 0? 0: 1);
             checksums_info.Transmit.UdpChecksum =
-                (addr->UDPChecksum != 0? 0: 1);
+                (addr->PseudoUDPChecksum == 0? 0: 1);
             checksums_info.Transmit.IpHeaderChecksum =
-                (addr->IPv4Checksum != 0? 0: 1);
+                (addr->PseudoIPChecksum == 0? 0: 1);
         }
         else
         {
             checksums_info.Receive.TcpChecksumSucceeded =
-                (addr->TCPChecksum != 0? 0: 1);
+                (addr->PseudoTCPChecksum == 0? 0: 1);
             checksums_info.Receive.UdpChecksumSucceeded =
-                (addr->UDPChecksum != 0? 0: 1);
+                (addr->PseudoUDPChecksum == 0? 0: 1);
             checksums_info.Receive.IpChecksumSucceeded =
-                (addr->IPv4Checksum != 0? 0: 1);
+                (addr->PseudoIPChecksum == 0? 0: 1);
         }
         NET_BUFFER_LIST_INFO(buffers, TcpIpChecksumNetBufferListInfo) =
             checksums_info.Value;
     }
+    else
+    {
+        if (addr->PseudoTCPChecksum != 0 || addr->PseudoUDPChecksum != 0 ||
+            addr->PseudoIPChecksum != 0)
+        {
+            status = STATUS_INVALID_PARAMETER;
+            goto windivert_write_exit;
+        }
+    }
 
     if (addr->Impostor)
     {