ringct: fuzz and harden Bulletproof verification

src/ringct/bulletproofs.cc

@@ -837,6 +837,7 @@ bool bulletproof_VERIFY(const std::vector<const Bulletproof*> &proofs)
     CHECK_AND_ASSERT_MES(is_reduced(proof.t), false, "Input scalar not in range");
 
     CHECK_AND_ASSERT_MES(proof.V.size() >= 1, false, "V does not have at least one element");
+    CHECK_AND_ASSERT_MES(proof.V.size() <= maxM, false, "V has too many elements");
     CHECK_AND_ASSERT_MES(proof.L.size() == proof.R.size(), false, "Mismatched L and R sizes");
     CHECK_AND_ASSERT_MES(proof.L.size() > 0, false, "Empty proof");
 

src/ringct/bulletproofs_plus.cc

@@ -827,6 +827,7 @@ try_again:
             CHECK_AND_ASSERT_MES(is_reduced(proof.d1), false, "Input scalar not in range");
 
             CHECK_AND_ASSERT_MES(proof.V.size() >= 1, false, "V does not have at least one element");
+            CHECK_AND_ASSERT_MES(proof.V.size() <= maxM, false, "V has too many elements");
             CHECK_AND_ASSERT_MES(proof.L.size() == proof.R.size(), false, "Mismatched L and R sizes");
             CHECK_AND_ASSERT_MES(proof.L.size() > 0, false, "Empty proof");
 

tests/fuzz/CMakeLists.txt

@@ -256,11 +256,8 @@ set_property(TARGET levin_fuzz_tests
 monero_add_minimal_executable(bulletproof_fuzz_tests bulletproof.cpp fuzzer.cpp)
 target_link_libraries(bulletproof_fuzz_tests
   PRIVATE
-    common
-    epee
-    ${Boost_THREAD_LIBRARY}
-    ${Boost_REGEX_LIBRARY}
-    ${Boost_PROGRAM_OPTIONS_LIBRARY}
+    ringct
+    serialization
     ${CMAKE_THREAD_LIBS_INIT}
     ${EXTRA_LIBRARIES}
     $ENV{LIB_FUZZING_ENGINE})

tests/fuzz/bulletproof.cpp

@@ -27,17 +27,39 @@
 // THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include "include_base_utils.h"
-#include "file_io_utils.h"
-#include "cryptonote_basic/blobdatatype.h"
-#include "cryptonote_basic/cryptonote_basic.h"
-#include "cryptonote_basic/cryptonote_format_utils.h"
 #include "fuzzer.h"
+#include "ringct/bulletproofs.h"
+#include "serialization/binary_utils.h"
+
+#include <string>
+#include <utility>
+
+namespace
+{
+  struct fuzz_input
+  {
+    rct::keyV commitments;
+    rct::Bulletproof proof;
+
+    BEGIN_SERIALIZE_OBJECT()
+      FIELD(commitments)
+      FIELD(proof)
+    END_SERIALIZE()
+  };
+}
 
 BEGIN_INIT_SIMPLE_FUZZER()
 END_INIT_SIMPLE_FUZZER()
 
 BEGIN_SIMPLE_FUZZER()
-  binary_archive<false> ba{{buf, len}};
-  rct::Bulletproof proof{};
-  ::serialization::serialize(ba, proof);
+  if (len > 4096)
+    return 0;
+
+  fuzz_input input;
+  const std::string blob{reinterpret_cast<const char*>(buf), len};
+  if (!serialization::parse_binary(blob, input))
+    return 0;
+
+  input.proof.V = std::move(input.commitments);
+  rct::bulletproof_VERIFY(input.proof);
 END_SIMPLE_FUZZER()

tests/unit_tests/bulletproofs.cpp

@@ -77,6 +77,20 @@ TEST(bulletproofs, valid_multi_random)
   }
 }
 
+TEST(bulletproofs, invalid_too_many_outputs)
+{
+  std::vector<uint64_t> amounts(16, 0);
+  rct::keyV gamma(16);
+  for (rct::key &mask: gamma)
+    mask = rct::skGen();
+  rct::Bulletproof proof = bulletproof_PROVE(amounts, gamma);
+  ASSERT_TRUE(rct::bulletproof_VERIFY(proof));
+  proof.V.push_back(proof.V.back());
+  proof.L.push_back(proof.L.back());
+  proof.R.push_back(proof.R.back());
+  ASSERT_FALSE(rct::bulletproof_VERIFY(proof));
+}
+
 TEST(bulletproofs, multi_splitting)
 {
   rct::ctkeyV sc, pc;

tests/unit_tests/bulletproofs_plus.cpp

@@ -77,6 +77,20 @@ TEST(bulletproofs_plus, valid_multi_random)
   }
 }
 
+TEST(bulletproofs_plus, invalid_too_many_outputs)
+{
+  std::vector<uint64_t> amounts(16, 0);
+  rct::keyV gamma(16);
+  for (rct::key &mask: gamma)
+    mask = rct::skGen();
+  rct::BulletproofPlus proof = bulletproof_plus_PROVE(amounts, gamma);
+  ASSERT_TRUE(rct::bulletproof_plus_VERIFY(proof));
+  proof.V.push_back(proof.V.back());
+  proof.L.push_back(proof.L.back());
+  proof.R.push_back(proof.R.back());
+  ASSERT_FALSE(rct::bulletproof_plus_VERIFY(proof));
+}
+
 TEST(bulletproofs_plus, valid_aggregated)
 {
   static const size_t N_PROOFS = 8;