1 files changed, 36 insertions, 0 deletions
diff --git a/security/nss/fuzz/mpi_expmod_target.cc b/security/nss/fuzz/mpi_expmod_target.cc
new file mode 100644
index 0000000000..b9be5854fb
--- /dev/null
+++ b/security/nss/fuzz/mpi_expmod_target.cc
@@ -0,0 +1,36 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * This target fuzzes NSS mpi against openssl bignum.
+ * It therefore requires openssl to be installed.
+ */
+
+#include "mpi_helper.h"
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  // We require at least size 3 to get two integers from Data.
+  if (size < 3) {
+    return 0;
+  }
+  INIT_FOUR_NUMBERS
+
+  auto modulus = get_modulus(data, size, ctx);
+  // Compare with OpenSSL exp mod
+  m1 = &std::get<1>(modulus);
+  // The exponent b (B) can get really big. Make it smaller if necessary.
+  if (MP_USED(&b) > 100) {
+    size_t shift = (MP_USED(&b) - 100) * MP_DIGIT_BIT;
+    mp_div_2d(&b, shift, &b, nullptr);
+    BN_rshift(B, B, shift);
+  }
+  check_equal(A, &a, max_size);
+  check_equal(B, &b, max_size);
+  check_equal(std::get<0>(modulus), m1, 3 * max_size);
+  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);
+
+  CLEANUP_AND_RETURN
+}