Fuzz more extension parsers in the cert parser

If we're going to rewrite the parsers later, let's cover them more
thoroughly.

Change-Id: Iab4bbb886da5e42caf4a6eff77cfedca8a33f085
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/64629
Reviewed-by: Bob Beck <bbe@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
Auto-Submit: David Benjamin <davidben@google.com>

1 files changed, 41 insertions, 9 deletions

diff --git a/fuzz/cert.cc b/fuzz/cert.cc
index e433450..2f4a547 100644
--- a/fuzz/cert.cc
+++ b/fuzz/cert.cc
@@ -19,24 +19,56 @@
 #include "../crypto/x509/internal.h"
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t *buf, size_t len) {
-  X509 *x509 = d2i_X509(NULL, &buf, len);
-  if (x509 != NULL) {
+  bssl::UniquePtr<X509> x509(d2i_X509(nullptr, &buf, len));
+  if (x509 != nullptr) {
     // Extract the public key.
-    EVP_PKEY_free(X509_get_pubkey(x509));
+    EVP_PKEY_free(X509_get_pubkey(x509.get()));
 
     // Fuzz some deferred parsing.
-    x509v3_cache_extensions(x509);
+    x509v3_cache_extensions(x509.get());
 
-    // Reserialize the structure.
-    uint8_t *der = NULL;
-    i2d_X509(x509, &der);
+    // Fuzz every supported extension.
+    for (int i = 0; i < X509_get_ext_count(x509.get()); i++) {
+      const X509_EXTENSION *ext = X509_get_ext(x509.get(), i);
+      void *parsed = X509V3_EXT_d2i(ext);
+      if (parsed != nullptr) {
+        int nid = OBJ_obj2nid(X509_EXTENSION_get_object(ext));
+        BSSL_CHECK(nid != NID_undef);
+
+        // Reserialize the extension. This should succeed if we were able to
+        // parse it.
+        // TODO(crbug.com/boringssl/352): Ideally we would also assert that
+        // |new_ext| is identical to |ext|, but our parser is not strict enough.
+        bssl::UniquePtr<X509_EXTENSION> new_ext(
+            X509V3_EXT_i2d(nid, X509_EXTENSION_get_critical(ext), parsed));
+        BSSL_CHECK(new_ext != nullptr);
+
+        // This can only fail if |ext| was not a supported type, but then
+        // |X509V3_EXT_d2i| should have failed.
+        BSSL_CHECK(X509V3_EXT_free(nid, parsed));
+      }
+    }
+
+    // Reserialize |x509|. This should succeed if we were able to parse it.
+    // TODO(crbug.com/boringssl/352): Ideally we would also assert the output
+    // matches the input, but our parser is not strict enough.
+    uint8_t *der = nullptr;
+    int der_len = i2d_X509(x509.get(), &der);
+    BSSL_CHECK(der_len > 0);
+    OPENSSL_free(der);
+
+    // Reserialize |x509|'s TBSCertificate without reusing the cached encoding.
+    // TODO(crbug.com/boringssl/352): Ideally we would also assert the output
+    // matches the input TBSCertificate, but our parser is not strict enough.
+    der = nullptr;
+    der_len = i2d_re_X509_tbs(x509.get(), &der);
+    BSSL_CHECK(der_len > 0);
     OPENSSL_free(der);
 
     BIO *bio = BIO_new(BIO_s_mem());
-    X509_print(bio, x509);
+    X509_print(bio, x509.get());
     BIO_free(bio);
   }
-  X509_free(x509);
   ERR_clear_error();
   return 0;
 }