1 files changed, 13 insertions, 9 deletions

diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index 54103fdb3..6664aea06 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -1153,7 +1153,7 @@ func (n *NIC) isInGroup(addr tcpip.Address) bool {
 	return joins != 0
 }
 
-func handlePacket(protocol tcpip.NetworkProtocolNumber, dst, src tcpip.Address, localLinkAddr, remotelinkAddr tcpip.LinkAddress, ref *referencedNetworkEndpoint, pkt PacketBuffer) {
+func handlePacket(protocol tcpip.NetworkProtocolNumber, dst, src tcpip.Address, localLinkAddr, remotelinkAddr tcpip.LinkAddress, ref *referencedNetworkEndpoint, pkt *PacketBuffer) {
 	r := makeRoute(protocol, dst, src, localLinkAddr, ref, false /* handleLocal */, false /* multicastLoop */)
 	r.RemoteLinkAddress = remotelinkAddr
 
@@ -1167,7 +1167,7 @@ func handlePacket(protocol tcpip.NetworkProtocolNumber, dst, src tcpip.Address,
 // Note that the ownership of the slice backing vv is retained by the caller.
 // This rule applies only to the slice itself, not to the items of the slice;
 // the ownership of the items is not retained by the caller.
-func (n *NIC) DeliverNetworkPacket(linkEP LinkEndpoint, remote, local tcpip.LinkAddress, protocol tcpip.NetworkProtocolNumber, pkt PacketBuffer) {
+func (n *NIC) DeliverNetworkPacket(remote, local tcpip.LinkAddress, protocol tcpip.NetworkProtocolNumber, pkt *PacketBuffer) {
 	n.mu.RLock()
 	enabled := n.mu.enabled
 	// If the NIC is not yet enabled, don't receive any packets.
@@ -1229,18 +1229,19 @@ func (n *NIC) DeliverNetworkPacket(linkEP LinkEndpoint, remote, local tcpip.Link
 	}
 
 	// TODO(gvisor.dev/issue/170): Not supporting iptables for IPv6 yet.
-	if protocol == header.IPv4ProtocolNumber {
+	// Loopback traffic skips the prerouting chain.
+	if protocol == header.IPv4ProtocolNumber && !n.isLoopback() {
 		// iptables filtering.
 		ipt := n.stack.IPTables()
 		address := n.primaryAddress(protocol)
-		if ok := ipt.Check(Prerouting, &pkt, nil, nil, address.Address, ""); !ok {
+		if ok := ipt.Check(Prerouting, pkt, nil, nil, address.Address, ""); !ok {
 			// iptables is telling us to drop the packet.
 			return
 		}
 	}
 
 	if ref := n.getRef(protocol, dst); ref != nil {
-		handlePacket(protocol, dst, src, linkEP.LinkAddress(), remote, ref, pkt)
+		handlePacket(protocol, dst, src, n.linkEP.LinkAddress(), remote, ref, pkt)
 		return
 	}
 
@@ -1298,24 +1299,27 @@ func (n *NIC) DeliverNetworkPacket(linkEP LinkEndpoint, remote, local tcpip.Link
 	}
 }
 
-func (n *NIC) forwardPacket(r *Route, protocol tcpip.NetworkProtocolNumber, pkt PacketBuffer) {
+func (n *NIC) forwardPacket(r *Route, protocol tcpip.NetworkProtocolNumber, pkt *PacketBuffer) {
 	// TODO(b/143425874) Decrease the TTL field in forwarded packets.
 	if linkHeaderLen := int(n.linkEP.MaxHeaderLength()); linkHeaderLen != 0 {
 		pkt.Header = buffer.NewPrependable(linkHeaderLen)
 	}
 
+	// WritePacket takes ownership of pkt, calculate numBytes first.
+	numBytes := pkt.Header.UsedLength() + pkt.Data.Size()
+
 	if err := n.linkEP.WritePacket(r, nil /* gso */, protocol, pkt); err != nil {
 		r.Stats().IP.OutgoingPacketErrors.Increment()
 		return
 	}
 
 	n.stats.Tx.Packets.Increment()
-	n.stats.Tx.Bytes.IncrementBy(uint64(pkt.Header.UsedLength() + pkt.Data.Size()))
+	n.stats.Tx.Bytes.IncrementBy(uint64(numBytes))
 }
 
 // DeliverTransportPacket delivers the packets to the appropriate transport
 // protocol endpoint.
-func (n *NIC) DeliverTransportPacket(r *Route, protocol tcpip.TransportProtocolNumber, pkt PacketBuffer) {
+func (n *NIC) DeliverTransportPacket(r *Route, protocol tcpip.TransportProtocolNumber, pkt *PacketBuffer) {
 	state, ok := n.stack.transportProtocols[protocol]
 	if !ok {
 		n.stack.stats.UnknownProtocolRcvdPackets.Increment()
@@ -1362,7 +1366,7 @@ func (n *NIC) DeliverTransportPacket(r *Route, protocol tcpip.TransportProtocolN
 
 // DeliverTransportControlPacket delivers control packets to the appropriate
 // transport protocol endpoint.
-func (n *NIC) DeliverTransportControlPacket(local, remote tcpip.Address, net tcpip.NetworkProtocolNumber, trans tcpip.TransportProtocolNumber, typ ControlType, extra uint32, pkt PacketBuffer) {
+func (n *NIC) DeliverTransportControlPacket(local, remote tcpip.Address, net tcpip.NetworkProtocolNumber, trans tcpip.TransportProtocolNumber, typ ControlType, extra uint32, pkt *PacketBuffer) {
 	state, ok := n.stack.transportProtocols[trans]
 	if !ok {
 		return