chunked: fix divide by zero in bloom filter

if the bloom filter size is zero, the "% size" operation fails with a
divide by zero.

Closes: #1903

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

pkg/chunked/bloom_filter.go

@@ -13,6 +13,9 @@ type bloomFilter struct {
 
 func newBloomFilter(size int, k uint32) *bloomFilter {
 	numElements := (size + 63) / 64
+	if numElements == 0 {
+		numElements = 1
+	}
 	return &bloomFilter{
 		bitArray: make([]uint64, numElements),
 		k:        k,
@@ -28,7 +31,7 @@ func newBloomFilterFromArray(bitArray []uint64, k uint32) *bloomFilter {
 
 func (bf *bloomFilter) hashFn(item []byte, seed uint32) (uint64, uint64) {
 	if len(item) == 0 {
-		return 0, 0
+		return 0, 1
 	}
 	mod := uint32(len(bf.bitArray) * 64)
 	seedSplit := seed % uint32(len(item))

pkg/chunked/bloom_filter_test.go

@@ -3,6 +3,7 @@ package chunked
 import (
 	"bytes"
 	"io"
+	"math/bits"
 	"testing"
 
 	digest "github.com/opencontainers/go-digest"
@@ -125,3 +126,27 @@ func TestBloomFilter(t *testing.T) {
 		assert.True(t, contains)
 	}
 }
+
+func TestStressBloomHashFn(t *testing.T) {
+	data := []byte("sha256:2f259bab93aaaaa2542ba43ef33eb990d0999ee1b9924b557b7be53c0b7a1bb9")
+	for numberHashes := uint32(1); numberHashes <= 3; numberHashes++ {
+		for size := 0; size < (1 << 16); size = size<<1 + 1 {
+			bloomFilter := newBloomFilter(size, numberHashes)
+			for seed := uint32(0); seed < numberHashes; seed++ {
+				index, mask := bloomFilter.hashFn([]byte{}, seed)
+				assert.True(t, int(index) < len(bloomFilter.bitArray))
+				assert.Equal(t, bits.OnesCount64(mask), 1)
+
+				index, mask = bloomFilter.hashFn(data, seed)
+				assert.True(t, int(index) < len(bloomFilter.bitArray))
+				assert.Equal(t, bits.OnesCount64(mask), 1)
+
+				index, mask = bloomFilter.hashFn(data[:len(data)/2], seed)
+				assert.True(t, int(index) < len(bloomFilter.bitArray))
+				assert.Equal(t, bits.OnesCount64(mask), 1)
+
+			}
+		}
+	}
+
+}