Remove tcp rtt tracking from the firewall (#1114)

firewall.go

@@ -2,7 +2,6 @@ package nebula
 
 import (
 	"crypto/sha256"
-	"encoding/binary"
 	"encoding/hex"
 	"errors"
 	"fmt"
@@ -22,17 +21,12 @@ import (
 	"github.com/slackhq/nebula/firewall"
 )
 
-const tcpACK = 0x10
-const tcpFIN = 0x01
-
 type FirewallInterface interface {
 	AddRule(incoming bool, proto uint8, startPort int32, endPort int32, groups []string, host string, ip *net.IPNet, localIp *net.IPNet, caName string, caSha string) error
 }
 
 type conn struct {
 	Expires time.Time // Time when this conntrack entry will expire
-	Sent    time.Time // If tcp rtt tracking is enabled this will be when Seq was last set
-	Seq     uint32    // If tcp rtt tracking is enabled this will be the seq we are looking for an ack
 
 	// record why the original connection passed the firewall, so we can re-validate
 	// after ruleset changes. Note, rulesVersion is a uint16 so that these two
@@ -66,8 +60,6 @@ type Firewall struct {
 	rulesVersion uint16
 
 	defaultLocalCIDRAny bool
-	trackTCPRTT         bool
-	metricTCPRTT        metrics.Histogram
 	incomingMetrics     firewallMetrics
 	outgoingMetrics     firewallMetrics
 
@@ -183,7 +175,6 @@ func NewFirewall(l *logrus.Logger, tcpTimeout, UDPTimeout, defaultTimeout time.D
 		hasSubnets:     len(c.Details.Subnets) > 0,
 		l:              l,
 
-		metricTCPRTT: metrics.GetOrRegisterHistogram("network.tcp.rtt", nil, metrics.NewExpDecaySample(1028, 0.015)),
 		incomingMetrics: firewallMetrics{
 			droppedLocalIP:  metrics.GetOrRegisterCounter("firewall.incoming.dropped.local_ip", nil),
 			droppedRemoteIP: metrics.GetOrRegisterCounter("firewall.incoming.dropped.remote_ip", nil),
@@ -422,9 +413,9 @@ var ErrNoMatchingRule = errors.New("no matching rule in firewall table")
 
 // Drop returns an error if the packet should be dropped, explaining why. It
 // returns nil if the packet should not be dropped.
-func (f *Firewall) Drop(packet []byte, fp firewall.Packet, incoming bool, h *HostInfo, caPool *cert.NebulaCAPool, localCache firewall.ConntrackCache) error {
+func (f *Firewall) Drop(fp firewall.Packet, incoming bool, h *HostInfo, caPool *cert.NebulaCAPool, localCache firewall.ConntrackCache) error {
 	// Check if we spoke to this tuple, if we did then allow this packet
-	if f.inConns(packet, fp, incoming, h, caPool, localCache) {
+	if f.inConns(fp, h, caPool, localCache) {
 		return nil
 	}
 
@@ -462,7 +453,7 @@ func (f *Firewall) Drop(packet []byte, fp firewall.Packet, incoming bool, h *Hos
 	}
 
 	// We always want to conntrack since it is a faster operation
-	f.addConn(packet, fp, incoming)
+	f.addConn(fp, incoming)
 
 	return nil
 }
@@ -491,7 +482,7 @@ func (f *Firewall) EmitStats() {
 	metrics.GetOrRegisterGauge("firewall.rules.hash", nil).Update(int64(f.GetRuleHashFNV()))
 }
 
-func (f *Firewall) inConns(packet []byte, fp firewall.Packet, incoming bool, h *HostInfo, caPool *cert.NebulaCAPool, localCache firewall.ConntrackCache) bool {
+func (f *Firewall) inConns(fp firewall.Packet, h *HostInfo, caPool *cert.NebulaCAPool, localCache firewall.ConntrackCache) bool {
 	if localCache != nil {
 		if _, ok := localCache[fp]; ok {
 			return true
@@ -551,11 +542,6 @@ func (f *Firewall) inConns(packet []byte, fp firewall.Packet, incoming bool, h *
 	switch fp.Protocol {
 	case firewall.ProtoTCP:
 		c.Expires = time.Now().Add(f.TCPTimeout)
-		if incoming {
-			f.checkTCPRTT(c, packet)
-		} else {
-			setTCPRTTTracking(c, packet)
-		}
 	case firewall.ProtoUDP:
 		c.Expires = time.Now().Add(f.UDPTimeout)
 	default:
@@ -571,16 +557,13 @@ func (f *Firewall) inConns(packet []byte, fp firewall.Packet, incoming bool, h *
 	return true
 }
 
-func (f *Firewall) addConn(packet []byte, fp firewall.Packet, incoming bool) {
+func (f *Firewall) addConn(fp firewall.Packet, incoming bool) {
 	var timeout time.Duration
 	c := &conn{}
 
 	switch fp.Protocol {
 	case firewall.ProtoTCP:
 		timeout = f.TCPTimeout
-		if !incoming {
-			setTCPRTTTracking(c, packet)
-		}
 	case firewall.ProtoUDP:
 		timeout = f.UDPTimeout
 	default:
@@ -1017,42 +1000,3 @@ func parsePort(s string) (startPort, endPort int32, err error) {
 
 	return
 }
-
-// TODO: write tests for these
-func setTCPRTTTracking(c *conn, p []byte) {
-	if c.Seq != 0 {
-		return
-	}
-
-	ihl := int(p[0]&0x0f) << 2
-
-	// Don't track FIN packets
-	if p[ihl+13]&tcpFIN != 0 {
-		return
-	}
-
-	c.Seq = binary.BigEndian.Uint32(p[ihl+4 : ihl+8])
-	c.Sent = time.Now()
-}
-
-func (f *Firewall) checkTCPRTT(c *conn, p []byte) bool {
-	if c.Seq == 0 {
-		return false
-	}
-
-	ihl := int(p[0]&0x0f) << 2
-	if p[ihl+13]&tcpACK == 0 {
-		return false
-	}
-
-	// Deal with wrap around, signed int cuts the ack window in half
-	// 0 is a bad ack, no data acknowledged
-	// positive number is a bad ack, ack is over half the window away
-	if int32(c.Seq-binary.BigEndian.Uint32(p[ihl+8:ihl+12])) >= 0 {
-		return false
-	}
-
-	f.metricTCPRTT.Update(time.Since(c.Sent).Nanoseconds())
-	c.Seq = 0
-	return true
-}