Fix concurrent map read and write in socket dataset (elastic#21690)

This fixes a panic caused by a concurrent map read and write in Auditbeat's
system/socket dataset.

Fixes elastic#21192

CHANGELOG.next.asciidoc

@@ -195,6 +195,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - auditd: Fix typo in `event.action` of `removed-user-role-from`. {pull}19300[19300]
 - auditd: Fix typo in `event.action` of `used-suspicious-link`. {pull}19300[19300]
 - system/socket: Fix kprobe grouping to allow running more than one instance. {pull}20325[20325]
+- system/socket: Fixed a crash due to concurrent map read and write. {issue}21192[21192] {pull}21690[21690]
 
 *Filebeat*
 

x-pack/auditbeat/module/system/socket/events.go

@@ -872,8 +872,8 @@ type execveCall struct {
 	creds *commitCreds
 }
 
-func (e *execveCall) getProcess() process {
-	p := process{
+func (e *execveCall) getProcess() *process {
+	p := &process{
 		pid:     e.Meta.PID,
 		path:    readCString(e.Path[:]),
 		created: kernelTime(e.Meta.Timestamp),

x-pack/auditbeat/module/system/socket/socket_linux.go

@@ -158,7 +158,7 @@ func (m *MetricSet) Run(r mb.PushReporterV2) {
 	} else {
 		for _, p := range procs {
 			if i, err := p.Info(); err == nil {
-				process := process{
+				process := &process{
 					name:        i.Name,
 					pid:         uint32(i.PID),
 					args:        i.Args,

x-pack/auditbeat/module/system/socket/state.go

@@ -214,6 +214,9 @@ func (f *flow) Timestamp() time.Time {
 }
 
 type process struct {
+	// RWMutex is used to arbitrate reads and writes to resolvedDomains.
+	sync.RWMutex
+
 	pid                  uint32
 	name, path           string
 	args                 []string
@@ -229,6 +232,8 @@ type process struct {
 }
 
 func (p *process) addTransaction(tr dns.Transaction) {
+	p.Lock()
+	defer p.Unlock()
 	if p.resolvedDomains == nil {
 		p.resolvedDomains = make(map[string]string)
 	}
@@ -239,6 +244,8 @@ func (p *process) addTransaction(tr dns.Transaction) {
 
 // ResolveIP returns the domain associated with the given IP.
 func (p *process) ResolveIP(ip net.IP) (domain string, found bool) {
+	p.RLock()
+	defer p.RUnlock()
 	domain, found = p.resolvedDomains[ip.String()]
 	return
 }
@@ -542,13 +549,13 @@ func (s *state) ExpireOlder() {
 	s.dns.CleanUp()
 }
 
-func (s *state) CreateProcess(p process) error {
+func (s *state) CreateProcess(p *process) error {
 	if p.pid == 0 {
 		return errors.New("can't create process with PID 0")
 	}
 	s.Lock()
 	defer s.Unlock()
-	s.processes[p.pid] = &p
+	s.processes[p.pid] = p
 	if p.createdTime == (time.Time{}) {
 		p.createdTime = s.kernTimestampToTime(p.created)
 	}

x-pack/auditbeat/module/system/socket/state_test.go

@@ -11,6 +11,7 @@ import (
 	"fmt"
 	"net"
 	"os"
+	"sync"
 	"testing"
 	"time"
 
@@ -835,3 +836,28 @@ func TestSocketReuse(t *testing.T) {
 	}
 	assert.Len(t, flows, 1)
 }
+
+func TestProcessDNSRace(t *testing.T) {
+	p := new(process)
+	var wg sync.WaitGroup
+	wg.Add(2)
+	address := func(i byte) net.IP { return net.IPv4(172, 16, 0, i) }
+	go func() {
+		for i := byte(255); i > 0; i-- {
+			p.addTransaction(dns.Transaction{
+				Client:    net.UDPAddr{IP: net.IPv4(10, 20, 30, 40)},
+				Server:    net.UDPAddr{IP: net.IPv4(10, 20, 30, 41)},
+				Domain:    "example.net",
+				Addresses: []net.IP{address(i)},
+			})
+		}
+		wg.Done()
+	}()
+	go func() {
+		for i := byte(255); i > 0; i-- {
+			p.ResolveIP(address(i))
+		}
+		wg.Done()
+	}()
+	wg.Wait()
+}