From b660f16d18827f0310594c80d9387de11430f15f Mon Sep 17 00:00:00 2001
From: Nayana Bidari <nybidari@google.com>
Date: Fri, 27 Mar 2020 12:18:45 -0700
Subject: Support for connection tracking of TCP packets.

Connection tracking is used to track packets in prerouting and
output hooks of iptables. The NAT rules modify the tuples in
connections. The connection tracking code modifies the packets by
looking at the modified tuples.
---
 pkg/tcpip/network/ipv4/ipv4.go | 46 ++++++++++++++++++++++++++++++++++++++----
 1 file changed, 42 insertions(+), 4 deletions(-)

(limited to 'pkg/tcpip/network/ipv4')

diff --git a/pkg/tcpip/network/ipv4/ipv4.go b/pkg/tcpip/network/ipv4/ipv4.go
index 1d61fddad..9db42b2a4 100644
--- a/pkg/tcpip/network/ipv4/ipv4.go
+++ b/pkg/tcpip/network/ipv4/ipv4.go
@@ -252,11 +252,31 @@ func (e *endpoint) WritePacket(r *stack.Route, gso *stack.GSO, params stack.Netw
 	// iptables filtering. All packets that reach here are locally
 	// generated.
 	ipt := e.stack.IPTables()
-	if ok := ipt.Check(stack.Output, pkt); !ok {
+	if ok := ipt.Check(stack.Output, &pkt, gso, r, ""); !ok {
 		// iptables is telling us to drop the packet.
 		return nil
 	}
 
+	if pkt.NatDone {
+		// If the packet is manipulated as per NAT Ouput rules, handle packet
+		// based on destination address and do not send the packet to link layer.
+		netHeader := header.IPv4(pkt.NetworkHeader)
+		ep, err := e.stack.FindNetworkEndpoint(header.IPv4ProtocolNumber, netHeader.DestinationAddress())
+		if err == nil {
+			src := netHeader.SourceAddress()
+			dst := netHeader.DestinationAddress()
+			route := r.ReverseRoute(src, dst)
+
+			views := make([]buffer.View, 1, 1+len(pkt.Data.Views()))
+			views[0] = pkt.Header.View()
+			views = append(views, pkt.Data.Views()...)
+			packet := stack.PacketBuffer{
+				Data: buffer.NewVectorisedView(len(views[0])+pkt.Data.Size(), views)}
+			ep.HandlePacket(&route, packet)
+			return nil
+		}
+	}
+
 	if r.Loop&stack.PacketLoop != 0 {
 		// The inbound path expects the network header to still be in
 		// the PacketBuffer's Data field.
@@ -302,8 +322,8 @@ func (e *endpoint) WritePackets(r *stack.Route, gso *stack.GSO, pkts stack.Packe
 	// iptables filtering. All packets that reach here are locally
 	// generated.
 	ipt := e.stack.IPTables()
-	dropped := ipt.CheckPackets(stack.Output, pkts)
-	if len(dropped) == 0 {
+	dropped, natPkts := ipt.CheckPackets(stack.Output, pkts, gso, r)
+	if len(dropped) == 0 && len(natPkts) == 0 {
 		// Fast path: If no packets are to be dropped then we can just invoke the
 		// faster WritePackets API directly.
 		n, err := e.linkEP.WritePackets(r, gso, pkts, ProtocolNumber)
@@ -318,6 +338,24 @@ func (e *endpoint) WritePackets(r *stack.Route, gso *stack.GSO, pkts stack.Packe
 		if _, ok := dropped[pkt]; ok {
 			continue
 		}
+		if _, ok := natPkts[pkt]; ok {
+			netHeader := header.IPv4(pkt.NetworkHeader)
+			ep, err := e.stack.FindNetworkEndpoint(header.IPv4ProtocolNumber, netHeader.DestinationAddress())
+			if err == nil {
+				src := netHeader.SourceAddress()
+				dst := netHeader.DestinationAddress()
+				route := r.ReverseRoute(src, dst)
+
+				views := make([]buffer.View, 1, 1+len(pkt.Data.Views()))
+				views[0] = pkt.Header.View()
+				views = append(views, pkt.Data.Views()...)
+				packet := stack.PacketBuffer{
+					Data: buffer.NewVectorisedView(len(views[0])+pkt.Data.Size(), views)}
+				ep.HandlePacket(&route, packet)
+				n++
+				continue
+			}
+		}
 		if err := e.linkEP.WritePacket(r, gso, ProtocolNumber, *pkt); err != nil {
 			r.Stats().IP.PacketsSent.IncrementBy(uint64(n))
 			return n, err
@@ -407,7 +445,7 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt stack.PacketBuffer) {
 	// iptables filtering. All packets that reach here are intended for
 	// this machine and will not be forwarded.
 	ipt := e.stack.IPTables()
-	if ok := ipt.Check(stack.Input, pkt); !ok {
+	if ok := ipt.Check(stack.Input, &pkt, nil, nil, ""); !ok {
 		// iptables is telling us to drop the packet.
 		return
 	}
-- 
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