fix(chstorage): check buckets size for overflow

internal/chstorage/querier_metrics_hist.go

@@ -92,8 +92,14 @@ func (p *expHistIterator) loadValue() (h histogram.Histogram, _ error) {
 		scale = 8
 	}
 
-	pSpans, pDeltas := convertBucketsLayout(p.values.positiveOffset[p.n], p.values.positiveBucketCounts[p.n], scaleDown)
-	nSpans, nDeltas := convertBucketsLayout(p.values.negativeOffset[p.n], p.values.negativeBucketCounts[p.n], scaleDown)
+	pSpans, pDeltas, err := convertBucketsLayout(p.values.positiveOffset[p.n], p.values.positiveBucketCounts[p.n], scaleDown)
+	if err != nil {
+		return h, errors.Wrap(err, "convert positive buckets")
+	}
+	nSpans, nDeltas, err := convertBucketsLayout(p.values.negativeOffset[p.n], p.values.negativeBucketCounts[p.n], scaleDown)
+	if err != nil {
+		return h, errors.Wrap(err, "convert negative buckets")
+	}
 
 	h = histogram.Histogram{
 		Schema: scale,
@@ -131,10 +137,13 @@ func (p *expHistIterator) loadValue() (h histogram.Histogram, _ error) {
 // to the range (base 1].
 //
 // scaleDown is the factor by which the buckets are scaled down. In other words 2^scaleDown buckets will be merged into one.
-func convertBucketsLayout(offset int32, bucketCounts []uint64, scaleDown int32) (spans []histogram.Span, deltas []int64) {
+func convertBucketsLayout(offset int32, bucketCounts []uint64, scaleDown int32) (spans []histogram.Span, deltas []int64, err error) {
 	numBuckets := len(bucketCounts)
-	if numBuckets == 0 {
-		return nil, nil
+	switch {
+	case numBuckets == 0:
+		return nil, nil, nil
+	case numBuckets > math.MaxInt32:
+		return nil, nil, errors.Errorf("too much buckets (%d is overflowing int32)", numBuckets)
 	}
 
 	var (
@@ -206,7 +215,7 @@ func convertBucketsLayout(offset int32, bucketCounts []uint64, scaleDown int32)
 	}
 	appendDelta(count)
 
-	return spans, deltas
+	return spans, deltas, nil
 }
 
 // At returns the current timestamp/value pair if the value is a float.