Fixes pyca#10422 -- don't crash when a PKCS#12 key and cert don't mat…

…ch (pyca#10423)

src/cryptography/hazmat/backends/openssl/backend.py

@@ -826,6 +826,15 @@ def serialize_key_and_certificates_to_pkcs12(
                     mac_iter,
                     0,
                 )
+                if p12 == self._ffi.NULL:
+                    errors = self._consume_errors()
+                    raise ValueError(
+                        (
+                            "Failed to create PKCS12 (does the key match the "
+                            "certificate?)"
+                        ),
+                        errors,
+                    )
 
             if (
                 self._lib.Cryptography_HAS_PKCS12_SET_MAC

tests/hazmat/primitives/test_pkcs12.py

@@ -657,6 +657,24 @@ def test_key_serialization_encryption_set_mac_unsupported(
                 b"name", cakey, cacert, [], algorithm
             )
 
+    @pytest.mark.supported(
+        only_if=lambda backend: backend._lib.Cryptography_HAS_PKCS12_SET_MAC,
+        skip_message="Requires OpenSSL with PKCS12_set_mac",
+    )
+    def test_set_mac_key_certificate_mismatch(self, backend):
+        cacert, _ = _load_ca(backend)
+        key = ec.generate_private_key(ec.SECP256R1())
+        encryption = (
+            serialization.PrivateFormat.PKCS12.encryption_builder()
+            .hmac_hash(hashes.SHA256())
+            .build(b"password")
+        )
+
+        with pytest.raises(ValueError):
+            serialize_key_and_certificates(
+                b"name", key, cacert, [], encryption
+            )
+
 
 @pytest.mark.skip_fips(
     reason="PKCS12 unsupported in FIPS mode. So much bad crypto in it."