reproduce decoder labels memory corruption

Signed-off-by: Piotr <17101802+thampiotr@users.noreply.github.com>

.github/workflows/ci.yml

@@ -41,6 +41,7 @@ jobs:
       - uses: ./.github/promci/actions/setup_environment
       - run: go test --tags=dedupelabels ./...
       - run: go test --tags=slicelabels -race ./cmd/prometheus
+      - run: go test --tags=slicelabels -race ./prompb/io/prometheus/client
       - run: go test --tags=forcedirectio -race ./tsdb/
       - run: GOARCH=386 go test ./...
       - uses: ./.github/promci/actions/check_proto

prompb/io/prometheus/client/decoder_test.go

@@ -17,13 +17,17 @@ import (
 	"bytes"
 	"encoding/binary"
 	"errors"
+	"fmt"
 	"io"
+	"math/rand"
 	"testing"
 
 	"github.com/gogo/protobuf/proto"
+	"github.com/prometheus/common/model"
 	"github.com/stretchr/testify/require"
 
 	"github.com/prometheus/prometheus/model/labels"
+	"github.com/prometheus/prometheus/util/pool"
 )
 
 const (
@@ -169,3 +173,74 @@ func TestMetricStreamingDecoder(t *testing.T) {
 	// Expect labels and metricBytes to be static and reusable even after parsing.
 	require.Equal(t, `{checksum="", path="github.com/prometheus/client_golang", version="(devel)"}`, firstMetricLset.String())
 }
+
+func TestMetricStreamingDecoder_LabelsCorruption(t *testing.T) {
+	lastScrapeSize := 0
+	var allPreviousLabels []labels.Labels
+	buffers := pool.New(128, 1024, 2, func(sz int) interface{} { return make([]byte, 0, sz) })
+	builder := labels.NewScratchBuilder(0)
+	for _, labelsCount := range []int{1, 2, 3, 5, 8, 5, 3, 2, 1} {
+		// Get buffer from pool like in scrape.go
+		b := buffers.Get(lastScrapeSize).([]byte)
+		buf := bytes.NewBuffer(b)
+
+		// Generate some scraped data to parse
+		mf := &MetricFamily{}
+		data := generateMetricFamilyText(labelsCount)
+		require.NoError(t, proto.UnmarshalText(data, mf))
+		protoBuf, err := proto.Marshal(mf)
+		require.NoError(t, err)
+		sizeBuf := make([]byte, binary.MaxVarintLen32)
+		sizeBufSize := binary.PutUvarint(sizeBuf, uint64(len(protoBuf)))
+		buf.Write(sizeBuf[:sizeBufSize])
+		buf.Write(protoBuf)
+
+		// Use decoder like protobufparse.go would
+		b = buf.Bytes()
+		d := NewMetricStreamingDecoder(b)
+		require.NoError(t, d.NextMetricFamily())
+		require.NoError(t, d.NextMetric())
+
+		// Get the labels
+		builder.Reset()
+		require.NoError(t, d.Label(&builder)) // <- this uses unsafe strings to create labels
+		lbs := builder.Labels()
+		allPreviousLabels = append(allPreviousLabels, lbs)
+
+		// Validate all labels seen so far remain valid and not corrupted
+		for _, l := range allPreviousLabels {
+			require.True(t, l.IsValid(model.LegacyValidation), "encountered corrupted labels: %v", l)
+		}
+
+		lastScrapeSize = len(b)
+		buffers.Put(b)
+	}
+}
+
+func generateLabels() string {
+	randomName := fmt.Sprintf("instance_%d", rand.Intn(1000))
+	randomValue := fmt.Sprintf("value_%d", rand.Intn(1000))
+	return fmt.Sprintf(`label: <
+    name: "%s"
+    value: "%s"
+  >`, randomName, randomValue)
+}
+
+func generateMetricFamilyText(labelsCount int) string {
+	randomName := fmt.Sprintf("metric_%d", rand.Intn(1000))
+	randomHelp := fmt.Sprintf("Test metric to demonstrate forced corruption %d.", rand.Intn(1000))
+	labels10 := ""
+	for i := 0; i < labelsCount; i++ {
+		labels10 += generateLabels()
+	}
+	return fmt.Sprintf(`name: "%s"
+help: "%s"
+type: GAUGE
+metric: <
+  %s
+  gauge: <
+    value: 1.0
+  >
+>
+`, randomName, randomHelp, labels10)
+}