tests: Add fuzzing harness for CFeeRate

src/Makefile.test.include

@@ -29,6 +29,7 @@ FUZZ_TARGETS = \
   test/fuzz/descriptor_parse \
   test/fuzz/diskblockindex_deserialize \
   test/fuzz/eval_script \
+  test/fuzz/fee_rate \
   test/fuzz/fee_rate_deserialize \
   test/fuzz/flat_file_pos_deserialize \
   test/fuzz/float \
@@ -434,6 +435,12 @@ test_fuzz_eval_script_LDADD = $(FUZZ_SUITE_LD_COMMON)
 test_fuzz_eval_script_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(LIBTOOL_APP_LDFLAGS)
 test_fuzz_eval_script_SOURCES = $(FUZZ_SUITE) test/fuzz/eval_script.cpp
 
+test_fuzz_fee_rate_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
+test_fuzz_fee_rate_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
+test_fuzz_fee_rate_LDADD = $(FUZZ_SUITE_LD_COMMON)
+test_fuzz_fee_rate_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(LIBTOOL_APP_LDFLAGS)
+test_fuzz_fee_rate_SOURCES = $(FUZZ_SUITE) test/fuzz/fee_rate.cpp
+
 test_fuzz_fee_rate_deserialize_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES) -DFEE_RATE_DESERIALIZE=1
 test_fuzz_fee_rate_deserialize_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
 test_fuzz_fee_rate_deserialize_LDADD = $(FUZZ_SUITE_LD_COMMON)

src/test/fuzz/fee_rate.cpp

@@ -0,0 +1,40 @@
+// Copyright (c) 2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <amount.h>
+#include <policy/feerate.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+
+#include <cstdint>
+#include <limits>
+#include <string>
+#include <vector>
+
+void test_one_input(const std::vector<uint8_t>& buffer)
+{
+    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
+    const CAmount satoshis_per_k = ConsumeMoney(fuzzed_data_provider);
+    const CFeeRate fee_rate{satoshis_per_k};
+
+    (void)fee_rate.GetFeePerK();
+    const size_t bytes = fuzzed_data_provider.ConsumeIntegral<size_t>();
+    if (!MultiplicationOverflow(static_cast<int64_t>(bytes), satoshis_per_k) && bytes <= static_cast<uint64_t>(std::numeric_limits<int64_t>::max())) {
+        (void)fee_rate.GetFee(bytes);
+    }
+    (void)fee_rate.ToString();
+
+    const CAmount another_satoshis_per_k = ConsumeMoney(fuzzed_data_provider);
+    CFeeRate larger_fee_rate{another_satoshis_per_k};
+    larger_fee_rate += fee_rate;
+    if (satoshis_per_k != 0 && another_satoshis_per_k != 0) {
+        assert(fee_rate < larger_fee_rate);
+        assert(!(fee_rate > larger_fee_rate));
+        assert(!(fee_rate == larger_fee_rate));
+        assert(fee_rate <= larger_fee_rate);
+        assert(!(fee_rate >= larger_fee_rate));
+        assert(fee_rate != larger_fee_rate);
+    }
+}

src/test/fuzz/util.h

@@ -5,6 +5,7 @@
 #ifndef BITCOIN_TEST_FUZZ_UTIL_H
 #define BITCOIN_TEST_FUZZ_UTIL_H
 
+#include <amount.h>
 #include <attributes.h>
 #include <optional.h>
 #include <script/script.h>
@@ -43,6 +44,11 @@ NODISCARD inline opcodetype ConsumeOpcodeType(FuzzedDataProvider& fuzzed_data_pr
     return static_cast<opcodetype>(fuzzed_data_provider.ConsumeIntegralInRange<uint32_t>(0, MAX_OPCODE));
 }
 
+NODISCARD inline CAmount ConsumeMoney(FuzzedDataProvider& fuzzed_data_provider) noexcept
+{
+    return fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(0, MAX_MONEY);
+}
+
 NODISCARD inline CScript ConsumeScript(FuzzedDataProvider& fuzzed_data_provider) noexcept
 {
     const std::vector<uint8_t> b = ConsumeRandomLengthByteVector(fuzzed_data_provider);
@@ -54,4 +60,27 @@ NODISCARD inline CScriptNum ConsumeScriptNum(FuzzedDataProvider& fuzzed_data_pro
     return CScriptNum{fuzzed_data_provider.ConsumeIntegral<int64_t>()};
 }
 
+template <typename T>
+bool MultiplicationOverflow(T i, T j)
+{
+    static_assert(std::is_integral<T>::value, "Integral required.");
+    if (std::numeric_limits<T>::is_signed) {
+        if (i > 0) {
+            if (j > 0) {
+                return i > (std::numeric_limits<T>::max() / j);
+            } else {
+                return j < (std::numeric_limits<T>::min() / i);
+            }
+        } else {
+            if (j > 0) {
+                return i < (std::numeric_limits<T>::min() / j);
+            } else {
+                return i != 0 && (j < (std::numeric_limits<T>::max() / i));
+            }
+        }
+    } else {
+        return j != 0 && i > std::numeric_limits<T>::max() / j;
+    }
+}
+
 #endif // BITCOIN_TEST_FUZZ_UTIL_H