Bug 1334106 - improve mpi fuzzing, r=me

3 files changed, 11 insertions, 0 deletions

diff --git a/fuzz/mpi_expmod_target.cc b/fuzz/mpi_expmod_target.cc
index ed31da354..d61039dc7 100644
--- a/fuzz/mpi_expmod_target.cc
+++ b/fuzz/mpi_expmod_target.cc
@@ -19,6 +19,10 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
   auto modulus = get_modulus(data, size, ctx);
   // Compare with OpenSSL exp mod
   m1 = &std::get<1>(modulus);
+  check_equal(A, &a, max_size);
+  check_equal(B, &b, max_size);
+  print_bn("A", A);
+  print_bn("B", B);
   assert(mp_exptmod(&a, &b, m1, &c) == MP_OKAY);
   (void)BN_mod_exp(C, A, B, std::get<0>(modulus), ctx);
   check_equal(C, &c, 2 * max_size);
diff --git a/fuzz/mpi_helper.cc b/fuzz/mpi_helper.cc
index 65cf4b9cd..d092fdb11 100644
--- a/fuzz/mpi_helper.cc
+++ b/fuzz/mpi_helper.cc
@@ -12,6 +12,12 @@ char *to_char(const uint8_t *x) {
   return reinterpret_cast<char *>(const_cast<unsigned char *>(x));
 }
 
+void print_bn(std::string label, BIGNUM *x) {
+  char *xc = BN_bn2hex(x);
+  std::cout << label << ": " << std::hex << xc << std::endl;
+  OPENSSL_free(xc);
+}
+
 // Check that the two numbers are equal.
 void check_equal(BIGNUM *b, mp_int *m, size_t max_size) {
   char *bnBc = BN_bn2hex(b);
diff --git a/fuzz/mpi_helper.h b/fuzz/mpi_helper.h
index 17383744b..ef7041b25 100644
--- a/fuzz/mpi_helper.h
+++ b/fuzz/mpi_helper.h
@@ -23,6 +23,7 @@ void parse_input(const uint8_t *data, size_t size, BIGNUM *A, BIGNUM *B,
 void parse_input(const uint8_t *data, size_t size, BIGNUM *A, mp_int *a);
 std::tuple<BIGNUM *, mp_int> get_modulus(const uint8_t *data, size_t size,
                                          BN_CTX *ctx);
+void print_bn(std::string label, BIGNUM *x);
 
 // Initialise MPI and BN variables
 // XXX: Also silence unused variable warnings for R.