trie: reject deletions when verifying range proofs (#667)

Co-authored-by: Péter Szilágyi <peterke@gmail.com>

trie/proof.go

@@ -472,12 +472,17 @@ func VerifyRangeProof(rootHash common.Hash, firstKey []byte, lastKey []byte, key
 	if len(keys) != len(values) {
 		return false, fmt.Errorf("inconsistent proof data, keys: %d, values: %d", len(keys), len(values))
 	}
-	// Ensure the received batch is monotonic increasing.
+	// Ensure the received batch is monotonic increasing and contains no deletions
 	for i := 0; i < len(keys)-1; i++ {
 		if bytes.Compare(keys[i], keys[i+1]) >= 0 {
 			return false, errors.New("range is not monotonically increasing")
 		}
 	}
+	for _, value := range values {
+		if len(value) == 0 {
+			return false, errors.New("range contains deletion")
+		}
+	}
 	// Special case, there is no edge proof at all. The given range is expected
 	// to be the whole leaf-set in the trie.
 	if proof == nil {

trie/proof_test.go

@@ -813,6 +813,85 @@ func TestBloatedProof(t *testing.T) {
 	}
 }
 
+// TestEmptyValueRangeProof tests normal range proof with both edge proofs
+// as the existent proof, but with an extra empty value included, which is a
+// noop technically, but practically should be rejected.
+func TestEmptyValueRangeProof(t *testing.T) {
+	trie, values := randomTrie(512)
+	var entries entrySlice
+	for _, kv := range values {
+		entries = append(entries, kv)
+	}
+	sort.Sort(entries)
+
+	// Create a new entry with a slightly modified key
+	mid := len(entries) / 2
+	key := common.CopyBytes(entries[mid-1].k)
+	for n := len(key) - 1; n >= 0; n-- {
+		if key[n] < 0xff {
+			key[n]++
+			break
+		}
+	}
+	noop := &kv{key, []byte{}, false}
+	entries = append(append(append([]*kv{}, entries[:mid]...), noop), entries[mid:]...)
+
+	start, end := 1, len(entries)-1
+
+	proof := memorydb.New()
+	if err := trie.Prove(entries[start].k, 0, proof); err != nil {
+		t.Fatalf("Failed to prove the first node %v", err)
+	}
+	if err := trie.Prove(entries[end-1].k, 0, proof); err != nil {
+		t.Fatalf("Failed to prove the last node %v", err)
+	}
+	var keys [][]byte
+	var vals [][]byte
+	for i := start; i < end; i++ {
+		keys = append(keys, entries[i].k)
+		vals = append(vals, entries[i].v)
+	}
+	_, err := VerifyRangeProof(trie.Hash(), keys[0], keys[len(keys)-1], keys, vals, proof)
+	if err == nil {
+		t.Fatalf("Expected failure on noop entry")
+	}
+}
+
+// TestAllElementsEmptyValueRangeProof tests the range proof with all elements,
+// but with an extra empty value included, which is a noop technically, but
+// practically should be rejected.
+func TestAllElementsEmptyValueRangeProof(t *testing.T) {
+	trie, values := randomTrie(512)
+	var entries entrySlice
+	for _, kv := range values {
+		entries = append(entries, kv)
+	}
+	sort.Sort(entries)
+
+	// Create a new entry with a slightly modified key
+	mid := len(entries) / 2
+	key := common.CopyBytes(entries[mid-1].k)
+	for n := len(key) - 1; n >= 0; n-- {
+		if key[n] < 0xff {
+			key[n]++
+			break
+		}
+	}
+	noop := &kv{key, []byte{}, false}
+	entries = append(append(append([]*kv{}, entries[:mid]...), noop), entries[mid:]...)
+
+	var keys [][]byte
+	var vals [][]byte
+	for i := 0; i < len(entries); i++ {
+		keys = append(keys, entries[i].k)
+		vals = append(vals, entries[i].v)
+	}
+	_, err := VerifyRangeProof(trie.Hash(), nil, nil, keys, vals, nil)
+	if err == nil {
+		t.Fatalf("Expected failure on noop entry")
+	}
+}
+
 // mutateByte changes one byte in b.
 func mutateByte(b []byte) {
 	for r := mrand.Intn(len(b)); ; {