tests: Add fuzzing harness for AdditionOverflow(...)

src/Makefile.test.include

@@ -3,6 +3,7 @@
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 FUZZ_TARGETS = \
+  test/fuzz/addition_overflow \
   test/fuzz/addr_info_deserialize \
   test/fuzz/addrdb \
   test/fuzz/address_deserialize \
@@ -280,6 +281,12 @@ endif
 
 if ENABLE_FUZZ
 
+test_fuzz_addition_overflow_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
+test_fuzz_addition_overflow_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
+test_fuzz_addition_overflow_LDADD = $(FUZZ_SUITE_LD_COMMON)
+test_fuzz_addition_overflow_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(LIBTOOL_APP_LDFLAGS)
+test_fuzz_addition_overflow_SOURCES = test/fuzz/addition_overflow.cpp
+
 test_fuzz_addr_info_deserialize_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES) -DADDR_INFO_DESERIALIZE=1
 test_fuzz_addr_info_deserialize_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
 test_fuzz_addr_info_deserialize_LDADD = $(FUZZ_SUITE_LD_COMMON)

src/test/fuzz/addition_overflow.cpp

@@ -0,0 +1,55 @@
+// 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 <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+
+#include <cstdint>
+#include <string>
+#include <vector>
+
+#if defined(__has_builtin)
+#if __has_builtin(__builtin_add_overflow)
+#define HAVE_BUILTIN_ADD_OVERFLOW
+#endif
+#elif defined(__GNUC__) && (__GNUC__ >= 5)
+#define HAVE_BUILTIN_ADD_OVERFLOW
+#endif
+
+namespace {
+template <typename T>
+void TestAdditionOverflow(FuzzedDataProvider& fuzzed_data_provider)
+{
+    const T i = fuzzed_data_provider.ConsumeIntegral<T>();
+    const T j = fuzzed_data_provider.ConsumeIntegral<T>();
+    const bool is_addition_overflow_custom = AdditionOverflow(i, j);
+#if defined(HAVE_BUILTIN_ADD_OVERFLOW)
+    T result_builtin;
+    const bool is_addition_overflow_builtin = __builtin_add_overflow(i, j, &result_builtin);
+    assert(is_addition_overflow_custom == is_addition_overflow_builtin);
+    if (!is_addition_overflow_custom) {
+        assert(i + j == result_builtin);
+    }
+#else
+    if (!is_addition_overflow_custom) {
+        (void)(i + j);
+    }
+#endif
+}
+} // namespace
+
+void test_one_input(const std::vector<uint8_t>& buffer)
+{
+    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
+    TestAdditionOverflow<int64_t>(fuzzed_data_provider);
+    TestAdditionOverflow<uint64_t>(fuzzed_data_provider);
+    TestAdditionOverflow<int32_t>(fuzzed_data_provider);
+    TestAdditionOverflow<uint32_t>(fuzzed_data_provider);
+    TestAdditionOverflow<int16_t>(fuzzed_data_provider);
+    TestAdditionOverflow<uint16_t>(fuzzed_data_provider);
+    TestAdditionOverflow<char>(fuzzed_data_provider);
+    TestAdditionOverflow<unsigned char>(fuzzed_data_provider);
+    TestAdditionOverflow<signed char>(fuzzed_data_provider);
+}

src/test/fuzz/util.h

@@ -120,4 +120,15 @@ NODISCARD bool MultiplicationOverflow(const T i, const T j) noexcept
     }
 }
 
+template <class T>
+NODISCARD bool AdditionOverflow(const T i, const T j) noexcept
+{
+    static_assert(std::is_integral<T>::value, "Integral required.");
+    if (std::numeric_limits<T>::is_signed) {
+        return (i > 0 && j > std::numeric_limits<T>::max() - i) ||
+               (i < 0 && j < std::numeric_limits<T>::min() - i);
+    }
+    return std::numeric_limits<T>::max() - i < j;
+}
+
 #endif // BITCOIN_TEST_FUZZ_UTIL_H