[Auditbeat] Fix up socket dataset runaway CPU usage (elastic#19764)

* Fix up socket dataset
* Add Changelog entry

CHANGELOG.next.asciidoc

@@ -148,7 +148,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - system/package: Fix parsing of Installed-Size field of DEB packages. {issue}16661[16661] {pull}17188[17188]
 - system module: Fix panic during initialisation when /proc/stat can't be read. {pull}17569[17569]
 - system/package: Fix an error that can occur while trying to persist package metadata. {issue}18536[18536] {pull}18887[18887]
-- system/socket: Fix dataset using 100% CPU and becoming unresponsive in some scenarios. {pull}19033[19033]
+- system/socket: Fix dataset using 100% CPU and becoming unresponsive in some scenarios. {pull}19033[19033] {pull}19764[19764]
 - system/socket: Fixed tracking of long-running connections. {pull}19033[19033]
 - system/package: Fix librpm loading on Fedora 31/32. {pull}NNNN[NNNN]
 - file_integrity: Create fsnotify watcher only when starting file_integrity module {pull}19505[19505]

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

@@ -523,7 +523,7 @@ func (s *state) ExpireOlder() {
 	deadline = s.clock().Add(-s.socketTimeout)
 	for item := s.socketLRU.peek(); item != nil && item.Timestamp().Before(deadline); {
 		if sock, ok := item.(*socket); ok {
-			s.onSockDestroyed(sock.sock, 0)
+			s.onSockDestroyed(sock.sock, sock, 0)
 		} else {
 			s.socketLRU.get()
 		}
@@ -704,13 +704,16 @@ func (s *state) OnSockDestroyed(ptr uintptr, pid uint32) error {
 	s.Lock()
 	defer s.Unlock()
 
-	return s.onSockDestroyed(ptr, pid)
+	return s.onSockDestroyed(ptr, nil, pid)
 }
 
-func (s *state) onSockDestroyed(ptr uintptr, pid uint32) error {
-	sock, found := s.socks[ptr]
-	if !found {
-		return nil
+func (s *state) onSockDestroyed(ptr uintptr, sock *socket, pid uint32) error {
+	var found bool
+	if sock == nil {
+		sock, found = s.socks[ptr]
+		if !found {
+			return nil
+		}
 	}
 	// Enrich with pid
 	if sock.pid == 0 && pid != 0 {

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

@@ -152,7 +152,6 @@ func TestTCPConnWithProcessSocketTimeouts(t *testing.T) {
 	lPort, rPort := be16(localPort), be16(remotePort)
 	lAddr, rAddr := ipv4(localIP), ipv4(remoteIP)
 	evs := []event{
-
 		callExecve(meta(1234, 1234, 1), []string{"/usr/bin/curl", "https://example.net/", "-o", "/tmp/site.html"}),
 		&commitCreds{Meta: meta(1234, 1234, 2), UID: 501, GID: 20, EUID: 501, EGID: 20},
 		&execveRet{Meta: meta(1234, 1234, 2), Retval: 1234},
@@ -302,6 +301,32 @@ func TestTCPConnWithProcessSocketTimeouts(t *testing.T) {
 	}
 }
 
+func TestSocketExpirationWithOverwrittenSockets(t *testing.T) {
+	const (
+		sock          uintptr = 0xff1234
+		flowTimeout           = time.Hour
+		socketTimeout         = time.Minute * 3
+		closeTimeout          = time.Minute
+	)
+	st := makeState(nil, (*logWrapper)(t), flowTimeout, socketTimeout, closeTimeout, time.Second)
+	now := time.Now()
+	st.clock = func() time.Time {
+		return now
+	}
+	if err := feedEvents([]event{
+		&inetCreate{Meta: meta(1234, 1236, 5), Proto: 0},
+		&sockInitData{Meta: meta(1234, 1236, 5), Sock: sock},
+		&inetCreate{Meta: meta(1234, 1237, 5), Proto: 0},
+		&sockInitData{Meta: meta(1234, 1237, 5), Sock: sock},
+	}, st, t); err != nil {
+		t.Fatal(err)
+	}
+	now = now.Add(closeTimeout + 1)
+	st.ExpireOlder()
+	now = now.Add(socketTimeout + 1)
+	st.ExpireOlder()
+}
+
 func TestUDPOutgoingSinglePacketWithProcess(t *testing.T) {
 	const (
 		localIP            = "192.168.33.10"