datapath-windows: Fix parsing of split buffers in OvsGetTcpHeader.

NdisGetDataBuffer() is called without providing a buffer to copy packet
data in case it is not contiguous.  So, it fails in some scenarios
where the packet is handled by the general network stack before OVS
and headers become split in multiple buffers.

Use existing helpers to retrieve the headers instead, they are using
OvsGetPacketBytes() which should be able to handle split data.

It might be a bit slower than getting direct pointers that may be
provided by NdisGetDataBuffer(), but it's better to optimize commonly
used OvsGetPacketBytes() helper in the future instead of optimizing
every single caller separately.  And we're still copying the TCP
header anyway.

Fixes: 9726a01 ("datapath-windows: Implement locking in conntrack NAT.")
Reported-at: openvswitch/ovs-issues#323
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Signed-off-by: 0-day Robot <robot@bytheb.org>

Author: igsilya

datapath-windows/ovsext/Conntrack.c

@@ -678,46 +678,43 @@ OvsGetTcpHeader(PNET_BUFFER_LIST nbl,
                 VOID *storage,
                 UINT32 *tcpPayloadLen)
 {
-    IPHdr *ipHdr;
-    IPv6Hdr *ipv6Hdr;
-    TCPHdr *tcp;
+    IPv6Hdr ipv6HdrStorage;
+    IPHdr ipHdrStorage;
+    const IPv6Hdr *ipv6Hdr;
+    const IPHdr *ipHdr;
+    const TCPHdr *tcp;
     VOID *dest = storage;
     uint16_t ipv6ExtLength = 0;
 
     if (layers->isIPv6) {
-        ipv6Hdr = NdisGetDataBuffer(NET_BUFFER_LIST_FIRST_NB(nbl),
-                                    layers->l4Offset + sizeof(TCPHdr),
-                                    NULL, 1, 0);
+        ipv6Hdr = OvsGetPacketBytes(nbl, sizeof *ipv6Hdr,
+                                    layers->l3Offset, &ipv6HdrStorage);
         if (ipv6Hdr == NULL) {
             return NULL;
         }
 
-        tcp = (TCPHdr *)((PCHAR)ipv6Hdr + layers->l4Offset);
-        ipv6Hdr = (IPv6Hdr *)((PCHAR)ipv6Hdr + layers->l3Offset);
-        if (tcp->doff * 4 >= sizeof *tcp) {
-            NdisMoveMemory(dest, tcp, sizeof(TCPHdr));
-            ipv6ExtLength = layers->l4Offset - layers->l3Offset - sizeof(IPv6Hdr);
-            *tcpPayloadLen = (ntohs(ipv6Hdr->payload_len) - ipv6ExtLength - TCP_HDR_LEN(tcp));
-            return storage;
+        tcp = OvsGetTcp(nbl, layers->l4Offset, dest);
+        if (tcp == NULL) {
+            return NULL;
         }
+
+        ipv6ExtLength = layers->l4Offset - layers->l3Offset - sizeof(IPv6Hdr);
+        *tcpPayloadLen = (ntohs(ipv6Hdr->payload_len) - ipv6ExtLength - TCP_HDR_LEN(tcp));
     } else {
-        ipHdr = NdisGetDataBuffer(NET_BUFFER_LIST_FIRST_NB(nbl),
-                                  layers->l4Offset + sizeof(TCPHdr),
-                                  NULL, 1 /*no align*/, 0);
+        ipHdr = OvsGetIp(nbl, layers->l3Offset, &ipHdrStorage);
         if (ipHdr == NULL) {
             return NULL;
         }
 
-        ipHdr = (IPHdr *)((PCHAR)ipHdr + layers->l3Offset);
-        tcp = (TCPHdr *)((PCHAR)ipHdr + ipHdr->ihl * 4);
-
-        if (tcp->doff * 4 >= sizeof *tcp) {
-            NdisMoveMemory(dest, tcp, sizeof(TCPHdr));
-            *tcpPayloadLen = TCP_DATA_LENGTH(ipHdr, tcp);
-            return storage;
+        tcp = OvsGetTcp(nbl, layers->l4Offset, dest);
+        if (tcp == NULL) {
+            return NULL;
         }
+
+        *tcpPayloadLen = TCP_DATA_LENGTH(ipHdr, tcp);
     }
-    return NULL;
+
+    return storage;
 }
 
 static UINT8