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Preserve conntrack table during firewall rules reload (SIGHUP) (#233) 

Currently, we drop the conntrack table when firewall rules change during a SIGHUP reload. This means responses to inflight HTTP requests can be dropped, among other issues. This change copies the conntrack table over to the new firewall (it holds the conntrack mutex lock during this process, to be safe).

This change also records which firewall rules hash each conntrack entry used, so that we can re-verify the rules after the new firewall has been loaded.
This commit is contained in:
Wade Simmons 2020-07-31 18:53:36 -04:00 committed by GitHub
parent 9b06748506
commit f3a6d8d990
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
3 changed files with 189 additions and 42 deletions
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104
firewall.go
View File

@ -15,6 +15,7 @@ import (
"time"
"github.com/rcrowley/go-metrics"
"github.com/sirupsen/logrus"
"github.com/slackhq/nebula/cert"
)
@ -37,13 +38,19 @@ type FirewallInterface interface {
type conn struct {
Expires time.Time // Time when this conntrack entry will expire
Seq uint32 // If tcp rtt tracking is enabled this will be the seq we are looking for an ack
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
// fields pack for free after the uint32 above
incoming bool
rulesVersion uint16
}
// TODO: need conntrack max tracked connections handling
type Firewall struct {
Conns map[FirewallPacket]*conn
Conntrack *FirewallConntrack
InRules *FirewallTable
OutRules *FirewallTable
@ -54,18 +61,23 @@ type Firewall struct {
UDPTimeout time.Duration //linux: 180s max
DefaultTimeout time.Duration //linux: 600s
TimerWheel *TimerWheel
// Used to ensure we don't emit local packets for ips we don't own
localIps *CIDRTree
connMutex sync.Mutex
rules string
rulesVersion uint16
trackTCPRTT bool
metricTCPRTT metrics.Histogram
}
type FirewallConntrack struct {
sync.Mutex
Conns map[FirewallPacket]*conn
TimerWheel *TimerWheel
}
type FirewallTable struct {
TCP firewallPort
UDP firewallPort
@ -171,10 +183,12 @@ func NewFirewall(tcpTimeout, UDPTimeout, defaultTimeout time.Duration, c *cert.N
}
return &Firewall{
Conntrack: &FirewallConntrack{
Conns: make(map[FirewallPacket]*conn),
TimerWheel: NewTimerWheel(min, max),
},
InRules: newFirewallTable(),
OutRules: newFirewallTable(),
TimerWheel: NewTimerWheel(min, max),
TCPTimeout: tcpTimeout,
UDPTimeout: UDPTimeout,
DefaultTimeout: defaultTimeout,
@ -354,7 +368,7 @@ var ErrNoMatchingRule = errors.New("no matching rule in firewall table")
// returns nil if the packet should not be dropped.
func (f *Firewall) Drop(packet []byte, fp FirewallPacket, incoming bool, h *HostInfo, caPool *cert.NebulaCAPool) error {
// Check if we spoke to this tuple, if we did then allow this packet
if f.inConns(packet, fp, incoming) {
if f.inConns(packet, fp, incoming, h, caPool) {
return nil
}
@ -398,26 +412,66 @@ func (f *Firewall) Destroy() {
}
func (f *Firewall) EmitStats() {
conntrackCount := len(f.Conns)
conntrack := f.Conntrack
conntrack.Lock()
conntrackCount := len(conntrack.Conns)
conntrack.Unlock()
metrics.GetOrRegisterGauge("firewall.conntrack.count", nil).Update(int64(conntrackCount))
metrics.GetOrRegisterGauge("firewall.rules.version", nil).Update(int64(f.rulesVersion))
}
func (f *Firewall) inConns(packet []byte, fp FirewallPacket, incoming bool) bool {
f.connMutex.Lock()
func (f *Firewall) inConns(packet []byte, fp FirewallPacket, incoming bool, h *HostInfo, caPool *cert.NebulaCAPool) bool {
conntrack := f.Conntrack
conntrack.Lock()
// Purge every time we test
ep, has := f.TimerWheel.Purge()
ep, has := conntrack.TimerWheel.Purge()
if has {
f.evict(ep)
}
c, ok := f.Conns[fp]
c, ok := conntrack.Conns[fp]
if !ok {
f.connMutex.Unlock()
conntrack.Unlock()
return false
}
if c.rulesVersion != f.rulesVersion {
// This conntrack entry was for an older rule set, validate
// it still passes with the current rule set
table := f.OutRules
if c.incoming {
table = f.InRules
}
// We now know which firewall table to check against
if !table.match(fp, c.incoming, h.ConnectionState.peerCert, caPool) {
if l.Level >= logrus.DebugLevel {
h.logger().
WithField("fwPacket", fp).
WithField("incoming", c.incoming).
WithField("rulesVersion", f.rulesVersion).
WithField("oldRulesVersion", c.rulesVersion).
Debugln("dropping old conntrack entry, does not match new ruleset")
}
delete(conntrack.Conns, fp)
conntrack.Unlock()
return false
}
if l.Level >= logrus.DebugLevel {
h.logger().
WithField("fwPacket", fp).
WithField("incoming", c.incoming).
WithField("rulesVersion", f.rulesVersion).
WithField("oldRulesVersion", c.rulesVersion).
Debugln("keeping old conntrack entry, does match new ruleset")
}
c.rulesVersion = f.rulesVersion
}
switch fp.Protocol {
case fwProtoTCP:
c.Expires = time.Now().Add(f.TCPTimeout)
@ -432,7 +486,7 @@ func (f *Firewall) inConns(packet []byte, fp FirewallPacket, incoming bool) bool
c.Expires = time.Now().Add(f.DefaultTimeout)
}
f.connMutex.Unlock()
conntrack.Unlock()
return true
}
@ -453,14 +507,19 @@ func (f *Firewall) addConn(packet []byte, fp FirewallPacket, incoming bool) {
timeout = f.DefaultTimeout
}
f.connMutex.Lock()
if _, ok := f.Conns[fp]; !ok {
f.TimerWheel.Add(fp, timeout)
conntrack := f.Conntrack
conntrack.Lock()
if _, ok := conntrack.Conns[fp]; !ok {
conntrack.TimerWheel.Add(fp, timeout)
}
// Record which rulesVersion allowed this connection, so we can retest after
// firewall reload
c.incoming = incoming
c.rulesVersion = f.rulesVersion
c.Expires = time.Now().Add(timeout)
f.Conns[fp] = c
f.connMutex.Unlock()
conntrack.Conns[fp] = c
conntrack.Unlock()
}
// Evict checks if a conntrack entry has expired, if so it is removed, if not it is re-added to the wheel
@ -468,7 +527,8 @@ func (f *Firewall) addConn(packet []byte, fp FirewallPacket, incoming bool) {
func (f *Firewall) evict(p FirewallPacket) {
//TODO: report a stat if the tcp rtt tracking was never resolved?
// Are we still tracking this conn?
t, ok := f.Conns[p]
conntrack := f.Conntrack
t, ok := conntrack.Conns[p]
if !ok {
return
}
@ -477,12 +537,12 @@ func (f *Firewall) evict(p FirewallPacket) {
// Timeout is in the future, re-add the timer
if newT > 0 {
f.TimerWheel.Add(p, newT)
conntrack.TimerWheel.Add(p, newT)
return
}
// This conn is done
delete(f.Conns, p)
delete(conntrack.Conns, p)
}
func (ft *FirewallTable) match(p FirewallPacket, incoming bool, c *cert.NebulaCertificate, caPool *cert.NebulaCAPool) bool {

106
firewall_test.go
View File

@ -17,37 +17,39 @@ import (
func TestNewFirewall(t *testing.T) {
c := &cert.NebulaCertificate{}
fw := NewFirewall(time.Second, time.Minute, time.Hour, c)
assert.NotNil(t, fw.Conns)
conntrack := fw.Conntrack
assert.NotNil(t, conntrack)
assert.NotNil(t, conntrack.Conns)
assert.NotNil(t, conntrack.TimerWheel)
assert.NotNil(t, fw.InRules)
assert.NotNil(t, fw.OutRules)
assert.NotNil(t, fw.TimerWheel)
assert.Equal(t, time.Second, fw.TCPTimeout)
assert.Equal(t, time.Minute, fw.UDPTimeout)
assert.Equal(t, time.Hour, fw.DefaultTimeout)
assert.Equal(t, time.Hour, fw.TimerWheel.wheelDuration)
assert.Equal(t, time.Hour, fw.TimerWheel.wheelDuration)
assert.Equal(t, 3601, fw.TimerWheel.wheelLen)
assert.Equal(t, time.Hour, conntrack.TimerWheel.wheelDuration)
assert.Equal(t, time.Hour, conntrack.TimerWheel.wheelDuration)
assert.Equal(t, 3601, conntrack.TimerWheel.wheelLen)
fw = NewFirewall(time.Second, time.Hour, time.Minute, c)
assert.Equal(t, time.Hour, fw.TimerWheel.wheelDuration)
assert.Equal(t, 3601, fw.TimerWheel.wheelLen)
assert.Equal(t, time.Hour, conntrack.TimerWheel.wheelDuration)
assert.Equal(t, 3601, conntrack.TimerWheel.wheelLen)
fw = NewFirewall(time.Hour, time.Second, time.Minute, c)
assert.Equal(t, time.Hour, fw.TimerWheel.wheelDuration)
assert.Equal(t, 3601, fw.TimerWheel.wheelLen)
assert.Equal(t, time.Hour, conntrack.TimerWheel.wheelDuration)
assert.Equal(t, 3601, conntrack.TimerWheel.wheelLen)
fw = NewFirewall(time.Hour, time.Minute, time.Second, c)
assert.Equal(t, time.Hour, fw.TimerWheel.wheelDuration)
assert.Equal(t, 3601, fw.TimerWheel.wheelLen)
assert.Equal(t, time.Hour, conntrack.TimerWheel.wheelDuration)
assert.Equal(t, 3601, conntrack.TimerWheel.wheelLen)
fw = NewFirewall(time.Minute, time.Hour, time.Second, c)
assert.Equal(t, time.Hour, fw.TimerWheel.wheelDuration)
assert.Equal(t, 3601, fw.TimerWheel.wheelLen)
assert.Equal(t, time.Hour, conntrack.TimerWheel.wheelDuration)
assert.Equal(t, 3601, conntrack.TimerWheel.wheelLen)
fw = NewFirewall(time.Minute, time.Second, time.Hour, c)
assert.Equal(t, time.Hour, fw.TimerWheel.wheelDuration)
assert.Equal(t, 3601, fw.TimerWheel.wheelLen)
assert.Equal(t, time.Hour, conntrack.TimerWheel.wheelDuration)
assert.Equal(t, 3601, conntrack.TimerWheel.wheelLen)
}
func TestFirewall_AddRule(t *testing.T) {
@ -461,6 +463,74 @@ func TestFirewall_Drop3(t *testing.T) {
assert.Equal(t, fw.Drop([]byte{}, p, true, &h3, cp), ErrNoMatchingRule)
}
func TestFirewall_DropConntrackReload(t *testing.T) {
ob := &bytes.Buffer{}
out := l.Out
l.SetOutput(ob)
defer l.SetOutput(out)
p := FirewallPacket{
ip2int(net.IPv4(1, 2, 3, 4)),
ip2int(net.IPv4(1, 2, 3, 4)),
10,
90,
fwProtoUDP,
false,
}
ipNet := net.IPNet{
IP: net.IPv4(1, 2, 3, 4),
Mask: net.IPMask{255, 255, 255, 0},
}
c := cert.NebulaCertificate{
Details: cert.NebulaCertificateDetails{
Name: "host1",
Ips: []*net.IPNet{&ipNet},
Groups: []string{"default-group"},
InvertedGroups: map[string]struct{}{"default-group": {}},
Issuer: "signer-shasum",
},
}
h := HostInfo{
ConnectionState: &ConnectionState{
peerCert: &c,
},
hostId: ip2int(ipNet.IP),
}
h.CreateRemoteCIDR(&c)
fw := NewFirewall(time.Second, time.Minute, time.Hour, &c)
assert.Nil(t, fw.AddRule(true, fwProtoAny, 0, 0, []string{"any"}, "", nil, "", ""))
cp := cert.NewCAPool()
// Drop outbound
assert.Equal(t, fw.Drop([]byte{}, p, false, &h, cp), ErrNoMatchingRule)
// Allow inbound
resetConntrack(fw)
assert.NoError(t, fw.Drop([]byte{}, p, true, &h, cp))
// Allow outbound because conntrack
assert.NoError(t, fw.Drop([]byte{}, p, false, &h, cp))
oldFw := fw
fw = NewFirewall(time.Second, time.Minute, time.Hour, &c)
assert.Nil(t, fw.AddRule(true, fwProtoAny, 10, 10, []string{"any"}, "", nil, "", ""))
fw.Conntrack = oldFw.Conntrack
fw.rulesVersion = oldFw.rulesVersion + 1
// Allow outbound because conntrack and new rules allow port 10
assert.NoError(t, fw.Drop([]byte{}, p, false, &h, cp))
oldFw = fw
fw = NewFirewall(time.Second, time.Minute, time.Hour, &c)
assert.Nil(t, fw.AddRule(true, fwProtoAny, 11, 11, []string{"any"}, "", nil, "", ""))
fw.Conntrack = oldFw.Conntrack
fw.rulesVersion = oldFw.rulesVersion + 1
// Drop outbound because conntrack doesn't match new ruleset
assert.Equal(t, fw.Drop([]byte{}, p, false, &h, cp), ErrNoMatchingRule)
}
func BenchmarkLookup(b *testing.B) {
ml := func(m map[string]struct{}, a [][]string) {
for n := 0; n < b.N; n++ {
@ -861,7 +931,7 @@ func (mf *mockFirewall) AddRule(incoming bool, proto uint8, startPort int32, end
}
func resetConntrack(fw *Firewall) {
fw.connMutex.Lock()
fw.Conns = map[FirewallPacket]*conn{}
fw.connMutex.Unlock()
fw.Conntrack.Lock()
fw.Conntrack.Conns = map[FirewallPacket]*conn{}
fw.Conntrack.Unlock()
}

17
interface.go
View File

@ -219,11 +219,28 @@ func (f *Interface) reloadFirewall(c *Config) {
}
oldFw := f.firewall
conntrack := oldFw.Conntrack
conntrack.Lock()
defer conntrack.Unlock()
fw.rulesVersion = oldFw.rulesVersion + 1
// If rulesVersion is back to zero, we have wrapped all the way around. Be
// safe and just reset conntrack in this case.
if fw.rulesVersion == 0 {
l.WithField("firewallHash", fw.GetRuleHash()).
WithField("oldFirewallHash", oldFw.GetRuleHash()).
WithField("rulesVersion", fw.rulesVersion).
Warn("firewall rulesVersion has overflowed, resetting conntrack")
} else {
fw.Conntrack = conntrack
}
f.firewall = fw
oldFw.Destroy()
l.WithField("firewallHash", fw.GetRuleHash()).
WithField("oldFirewallHash", oldFw.GetRuleHash()).
WithField("rulesVersion", fw.rulesVersion).
Info("New firewall has been installed")
}