Cherry-pick #18738 to 7.x: Improve thread safety of fingerprint proce…

…ssor (#18926)

CHANGELOG.next.asciidoc

@@ -120,6 +120,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - [Autodiscover] Check if runner is already running before starting again. {pull}18564[18564]
 - Fix `keystore add` hanging under Windows. {issue}18649[18649] {pull}18654[18654]
 - Fix regression in `add_kubernetes_metadata`, so configured `indexers` and `matchers` are used if defaults are not disabled. {issue}18481[18481] {pull}18818[18818]
+- Fix potential race condition in fingerprint processor. {pull}18738[18738]
 
 *Auditbeat*
 

libbeat/processors/fingerprint/fingerprint.go

@@ -19,7 +19,6 @@ package fingerprint
 
 import (
 	"fmt"
-	"hash"
 	"io"
 	"time"
 
@@ -39,7 +38,7 @@ const processorName = "fingerprint"
 type fingerprint struct {
 	config Config
 	fields []string
-	hash   hash.Hash
+	hash   hashMethod
 }
 
 // New constructs a new fingerprint processor.
@@ -49,21 +48,23 @@ func New(cfg *common.Config) (processors.Processor, error) {
 		return nil, makeErrConfigUnpack(err)
 	}
 
-	fields := common.MakeStringSet(config.Fields...)
+	// The fields array must be sorted, to guarantee that we always
+	// get the same hash for a similar set of configured keys.
+	// The call `ToSlice` always returns a sorted slice.
+	fields := common.MakeStringSet(config.Fields...).ToSlice()
 
 	p := &fingerprint{
 		config: config,
-		hash:   config.Method(),
-		fields: fields.ToSlice(),
+		hash:   config.Method,
+		fields: fields,
 	}
 
 	return p, nil
 }
 
 // Run enriches the given event with fingerprint information
 func (p *fingerprint) Run(event *beat.Event) (*beat.Event, error) {
-	hashFn := p.hash
-	hashFn.Reset()
+	hashFn := p.hash()
 
 	err := p.writeFields(hashFn, event.Fields)
 	if err != nil {

libbeat/processors/fingerprint/fingerprint_test.go

@@ -24,11 +24,56 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
 	"github.com/elastic/beats/v7/libbeat/beat"
 	"github.com/elastic/beats/v7/libbeat/common"
 )
 
+func TestWithConfig(t *testing.T) {
+	cases := map[string]struct {
+		config common.MapStr
+		input  common.MapStr
+		want   string
+	}{
+		"hello world": {
+			config: common.MapStr{
+				"fields": []string{"message"},
+			},
+			input: common.MapStr{
+				"message": "hello world",
+			},
+			want: "50110bbfc1757f21caacc966b33f5ea2235c4176739447e0b3285dec4e1dd2a4",
+		},
+		"with string escaping": {
+			config: common.MapStr{
+				"fields": []string{"message"},
+			},
+			input: common.MapStr{
+				"message": `test message "hello world"`,
+			},
+			want: "14a0364b79acbe4c78dd5e77db2c93ae8c750518b32581927d50b3eef407184e",
+		},
+	}
+
+	for name, test := range cases {
+		t.Run(name, func(t *testing.T) {
+			config := common.MustNewConfigFrom(test.config)
+			p, err := New(config)
+			require.NoError(t, err)
+
+			testEvent := &beat.Event{
+				Timestamp: time.Now(),
+				Fields:    test.input.Clone(),
+			}
+			newEvent, err := p.Run(testEvent)
+			v, err := newEvent.GetValue("fingerprint")
+			assert.NoError(t, err)
+			assert.Equal(t, test.want, v)
+		})
+	}
+}
+
 func TestHashMethods(t *testing.T) {
 	testFields := common.MapStr{
 		"field1":       "foo",
@@ -393,7 +438,10 @@ func BenchmarkHashMethods(b *testing.B) {
 		b.Run(method, func(b *testing.B) {
 			b.ResetTimer()
 			for _, e := range events {
-				p.Run(&e)
+				_, err := p.Run(&e)
+				if err != nil {
+					b.Fatal(err)
+				}
 			}
 		})
 	}