datapath-windows: Account for VLAN tag in tunnel Decap

Decap functions for tunneling protocols do not compute
the packet header offsets correctly when there is a VLAN
tag in the L2 header. This results in incorrect checksum
computation causing the packet to be dropped.

This patch adds support to account for the VLAN tag in the
packet if its present, and makes use of the OvsExtractLayers()
function to correctly compute the header offsets for different
layers.

Testing done:
- Tested Geneve, STT, Vxlan and Gre and verified that there
  are no regressions.
- Verified that packets with VLAN tags are correctly handled
  in the decap code of all tunneling protocols. Previously,
  this would result in packet drops due to invalid checksums
  being computed.
- Verified that non-VLAN tagged packets are handled correctly.

Signed-off-by: Shashank Ram <rams@vmware.com>
Acked-by: Anand Kumar <kumaranand@vmware.com>
Signed-off-by: Alin Gabriel Serdean <aserdean@ovn.org>

1 files changed, 31 insertions, 13 deletions

diff --git a/datapath-windows/ovsext/Stt.c b/datapath-windows/ovsext/Stt.c
index f98070f33..8eb71676a 100644
--- a/datapath-windows/ovsext/Stt.c
+++ b/datapath-windows/ovsext/Stt.c
@@ -415,9 +415,23 @@ ret_error:
  *----------------------------------------------------------------------------
  */
 static __inline NDIS_STATUS
-OvsValidateTCPChecksum(PNET_BUFFER_LIST curNbl, PNET_BUFFER curNb)
+OvsValidateTCPChecksum(PNET_BUFFER_LIST curNbl,
+                       PNET_BUFFER curNb,
+                       POVS_PACKET_HDR_INFO layers)
 {
+    PUINT8 buf;
+    PMDL curMdl;
     NDIS_TCP_IP_CHECKSUM_NET_BUFFER_LIST_INFO csumInfo;
+    NDIS_STATUS status;
+
+    curMdl = NET_BUFFER_CURRENT_MDL(curNb);
+    buf = (PUINT8)MmGetSystemAddressForMdlSafe(curMdl, LowPagePriority)
+        + NET_BUFFER_CURRENT_MDL_OFFSET(curNb);
+    if (!buf) {
+        status = NDIS_STATUS_INVALID_PACKET;
+        return status;
+    }
+
     csumInfo.Value = NET_BUFFER_LIST_INFO(curNbl,
                                           TcpIpChecksumNetBufferListInfo);
 
@@ -433,23 +447,22 @@ OvsValidateTCPChecksum(PNET_BUFFER_LIST curNbl, PNET_BUFFER curNb)
         return NDIS_STATUS_SUCCESS;
     }
 
-    EthHdr *eth = (EthHdr *)NdisGetDataBuffer(curNb, sizeof(EthHdr),
-                                              NULL, 1, 0);
-    if (eth == NULL) {
+    EthHdr *ethHdr = (EthHdr *)buf;
+    if (ethHdr == NULL) {
         return NDIS_STATUS_RESOURCES;
     }
 
-    if (eth->Type == ntohs(NDIS_ETH_TYPE_IPV4)) {
-        IPHdr *ip = (IPHdr *)((PCHAR)eth + sizeof *eth);
-        UINT32 l4Payload = ntohs(ip->tot_len) - ip->ihl * 4;
-        TCPHdr *tcp = (TCPHdr *)((PCHAR)ip + ip->ihl * 4);
+    if (ethHdr->Type == ntohs(NDIS_ETH_TYPE_IPV4)) {
+        IPHdr *ipHdr = (IPHdr *)(buf + layers->l3Offset);
+        UINT32 l4Payload = ntohs(ipHdr->tot_len) - ipHdr->ihl * 4;
+        TCPHdr *tcp = (TCPHdr *)(buf + layers->l4Offset);
         checkSum = tcp->check;
 
         tcp->check = 0;
-        tcp->check = IPPseudoChecksum(&ip->saddr, &ip->daddr,
+        tcp->check = IPPseudoChecksum(&ipHdr->saddr, &ipHdr->daddr,
                                       IPPROTO_TCP, (UINT16)l4Payload);
         tcp->check = CalculateChecksumNB(curNb, (UINT16)(l4Payload),
-                                         sizeof(EthHdr) + ip->ihl * 4);
+                                         layers->l4Offset);
         if (checkSum != tcp->check) {
             return NDIS_STATUS_INVALID_PACKET;
         }
@@ -912,18 +925,24 @@ OvsDecapStt(POVS_SWITCH_CONTEXT switchContext,
     SttHdr *sttHdr;
     char *sttBuf[STT_HDR_LEN];
     UINT32 advanceCnt, hdrLen;
+    OVS_PACKET_HDR_INFO layers = { 0 };
+
+    status = OvsExtractLayers(curNbl, &layers);
+    if (status != NDIS_STATUS_SUCCESS) {
+        return status;
+    }
 
     curNb = NET_BUFFER_LIST_FIRST_NB(curNbl);
     ASSERT(NET_BUFFER_NEXT_NB(curNb) == NULL);
 
     /* Validate the TCP Checksum */
-    status = OvsValidateTCPChecksum(curNbl, curNb);
+    status = OvsValidateTCPChecksum(curNbl, curNb, &layers);
     if (status != NDIS_STATUS_SUCCESS) {
         return status;
     }
 
     /* Skip Eth header */
-    hdrLen = sizeof(EthHdr);
+    hdrLen = layers.l3Offset;
     NdisAdvanceNetBufferDataStart(curNb, hdrLen, FALSE, NULL);
     advanceCnt = hdrLen;
 
@@ -996,7 +1015,6 @@ OvsDecapStt(POVS_SWITCH_CONTEXT switchContext,
     tunKey->pad = 0;
 
     /* Handle ECN */
-    OVS_PACKET_HDR_INFO layers = {0};
     if (0 != ipHdr->tos) {
         status = OvsExtractLayers(*newNbl, &layers);
         if (status != NDIS_STATUS_SUCCESS) {