tests: Add fuzzing harness for functions/classes in random.h

4 files changed, 62 insertions, 9 deletions

diff --git a/src/Makefile.test.include b/src/Makefile.test.include
index c01c9fc52a..059876bec8 100644
--- a/src/Makefile.test.include
+++ b/src/Makefile.test.include
@@ -91,6 +91,7 @@ FUZZ_TARGETS = \
   test/fuzz/psbt_input_deserialize \
   test/fuzz/psbt_output_deserialize \
   test/fuzz/pub_key_deserialize \
+  test/fuzz/random \
   test/fuzz/rolling_bloom_filter \
   test/fuzz/script \
   test/fuzz/script_deserialize \
@@ -819,6 +820,12 @@ test_fuzz_pub_key_deserialize_LDADD = $(FUZZ_SUITE_LD_COMMON)
 test_fuzz_pub_key_deserialize_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(LIBTOOL_APP_LDFLAGS)
 test_fuzz_pub_key_deserialize_SOURCES = $(FUZZ_SUITE) test/fuzz/deserialize.cpp
 
+test_fuzz_random_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
+test_fuzz_random_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
+test_fuzz_random_LDADD = $(FUZZ_SUITE_LD_COMMON)
+test_fuzz_random_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(LIBTOOL_APP_LDFLAGS)
+test_fuzz_random_SOURCES = $(FUZZ_SUITE) test/fuzz/random.cpp
+
 test_fuzz_rolling_bloom_filter_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
 test_fuzz_rolling_bloom_filter_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
 test_fuzz_rolling_bloom_filter_LDADD = $(FUZZ_SUITE_LD_COMMON)
diff --git a/src/random.h b/src/random.h
index 518a5cd3e3..4e4597cff6 100644
--- a/src/random.h
+++ b/src/random.h
@@ -103,7 +103,8 @@ void RandAddEvent(const uint32_t event_info) noexcept;
  *
  * This class is not thread-safe.
  */
-class FastRandomContext {
+class FastRandomContext
+{
 private:
     bool requires_seed;
     ChaCha20 rng;
@@ -155,7 +156,8 @@ public:
     }
 
     /** Generate a random (bits)-bit integer. */
-    uint64_t randbits(int bits) noexcept {
+    uint64_t randbits(int bits) noexcept
+    {
         if (bits == 0) {
             return 0;
         } else if (bits > 32) {
@@ -169,7 +171,9 @@ public:
         }
     }
 
-    /** Generate a random integer in the range [0..range). */
+    /** Generate a random integer in the range [0..range).
+     * Precondition: range > 0.
+     */
     uint64_t randrange(uint64_t range) noexcept
     {
         assert(range);
@@ -210,7 +214,7 @@ public:
  * debug mode detects and panics on. This is a known issue, see
  * https://stackoverflow.com/questions/22915325/avoiding-self-assignment-in-stdshuffle
  */
-template<typename I, typename R>
+template <typename I, typename R>
 void Shuffle(I first, I last, R&& rng)
 {
     while (first != last) {
@@ -233,7 +237,7 @@ static const int NUM_OS_RANDOM_BYTES = 32;
 /** Get 32 bytes of system entropy. Do not use this in application code: use
  * GetStrongRandBytes instead.
  */
-void GetOSRand(unsigned char *ent32);
+void GetOSRand(unsigned char* ent32);
 
 /** Check that OS randomness is available and returning the requested number
  * of bytes.
diff --git a/src/test/fuzz/random.cpp b/src/test/fuzz/random.cpp
new file mode 100644
index 0000000000..7df6594ad6
--- /dev/null
+++ b/src/test/fuzz/random.cpp
@@ -0,0 +1,31 @@
+// 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 <random.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+
+#include <algorithm>
+#include <cstdint>
+#include <string>
+#include <vector>
+
+void test_one_input(const std::vector<uint8_t>& buffer)
+{
+    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
+    FastRandomContext fast_random_context{ConsumeUInt256(fuzzed_data_provider)};
+    (void)fast_random_context.rand64();
+    (void)fast_random_context.randbits(fuzzed_data_provider.ConsumeIntegralInRange<int>(0, 64));
+    (void)fast_random_context.randrange(fuzzed_data_provider.ConsumeIntegralInRange<uint64_t>(FastRandomContext::min() + 1, FastRandomContext::max()));
+    (void)fast_random_context.randbytes(fuzzed_data_provider.ConsumeIntegralInRange<size_t>(0, 1024));
+    (void)fast_random_context.rand32();
+    (void)fast_random_context.rand256();
+    (void)fast_random_context.randbool();
+    (void)fast_random_context();
+
+    std::vector<int64_t> integrals = ConsumeRandomLengthIntegralVector<int64_t>(fuzzed_data_provider);
+    Shuffle(integrals.begin(), integrals.end(), fast_random_context);
+    std::shuffle(integrals.begin(), integrals.end(), fast_random_context);
+}
diff --git a/src/test/fuzz/util.h b/src/test/fuzz/util.h
index 10be2ebaf7..7004aff420 100644
--- a/src/test/fuzz/util.h
+++ b/src/test/fuzz/util.h
@@ -20,13 +20,13 @@
 #include <string>
 #include <vector>
 
-NODISCARD inline std::vector<uint8_t> ConsumeRandomLengthByteVector(FuzzedDataProvider& fuzzed_data_provider, size_t max_length = 4096) noexcept
+NODISCARD inline std::vector<uint8_t> ConsumeRandomLengthByteVector(FuzzedDataProvider& fuzzed_data_provider, const size_t max_length = 4096) noexcept
 {
     const std::string s = fuzzed_data_provider.ConsumeRandomLengthString(max_length);
     return {s.begin(), s.end()};
 }
 
-NODISCARD inline std::vector<std::string> ConsumeRandomLengthStringVector(FuzzedDataProvider& fuzzed_data_provider, size_t max_vector_size = 16, size_t max_string_length = 16) noexcept
+NODISCARD inline std::vector<std::string> ConsumeRandomLengthStringVector(FuzzedDataProvider& fuzzed_data_provider, const size_t max_vector_size = 16, const size_t max_string_length = 16) noexcept
 {
     const size_t n_elements = fuzzed_data_provider.ConsumeIntegralInRange<size_t>(0, max_vector_size);
     std::vector<std::string> r;
@@ -37,7 +37,18 @@ NODISCARD inline std::vector<std::string> ConsumeRandomLengthStringVector(Fuzzed
 }
 
 template <typename T>
-NODISCARD inline Optional<T> ConsumeDeserializable(FuzzedDataProvider& fuzzed_data_provider, size_t max_length = 4096) noexcept
+NODISCARD inline std::vector<T> ConsumeRandomLengthIntegralVector(FuzzedDataProvider& fuzzed_data_provider, const size_t max_vector_size = 16) noexcept
+{
+    const size_t n_elements = fuzzed_data_provider.ConsumeIntegralInRange<size_t>(0, max_vector_size);
+    std::vector<T> r;
+    for (size_t i = 0; i < n_elements; ++i) {
+        r.push_back(fuzzed_data_provider.ConsumeIntegral<T>());
+    }
+    return r;
+}
+
+template <typename T>
+NODISCARD inline Optional<T> ConsumeDeserializable(FuzzedDataProvider& fuzzed_data_provider, const size_t max_length = 4096) noexcept
 {
     const std::vector<uint8_t> buffer = ConsumeRandomLengthByteVector(fuzzed_data_provider, max_length);
     CDataStream ds{buffer, SER_NETWORK, INIT_PROTO_VERSION};
@@ -81,7 +92,7 @@ NODISCARD inline uint256 ConsumeUInt256(FuzzedDataProvider& fuzzed_data_provider
 }
 
 template <typename T>
-bool MultiplicationOverflow(T i, T j)
+NODISCARD bool MultiplicationOverflow(const T i, const T j) noexcept
 {
     static_assert(std::is_integral<T>::value, "Integral required.");
     if (std::numeric_limits<T>::is_signed) {