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       1                 :            : /*
       2                 :            :  * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
       3                 :            :  *
       4                 :            :  * Licensed under the Apache License, Version 2.0 (the "License").
       5                 :            :  * You may not use this file except in compliance with the License.
       6                 :            :  * A copy of the License is located at
       7                 :            :  *
       8                 :            :  *  http://aws.amazon.com/apache2.0
       9                 :            :  *
      10                 :            :  * or in the "license" file accompanying this file. This file is distributed
      11                 :            :  * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
      12                 :            :  * express or implied. See the License for the specific language governing
      13                 :            :  * permissions and limitations under the License.
      14                 :            :  */
      15                 :            : 
      16                 :            : #include "tls/extensions/s2n_cookie.h"
      17                 :            : #include "tls/s2n_tls.h"
      18                 :            : #include "utils/s2n_random.h"
      19                 :            : 
      20                 :            : /*
      21                 :            :  *= https://www.rfc-editor.org/rfc/rfc8446#section-4.2.2
      22                 :            :  *# When sending the new ClientHello, the client MUST copy
      23                 :            :  *# the contents of the extension received in the HelloRetryRequest into
      24                 :            :  *# a "cookie" extension in the new ClientHello.
      25                 :            :  *
      26                 :            :  * If the server sent a cookie, send it back.
      27                 :            :  */
      28                 :            : static bool s2n_client_cookie_should_send(struct s2n_connection *conn)
      29                 :         40 : {
      30 [ +  - ][ +  + ]:         40 :     return conn && conn->cookie.size > 0;
      31                 :         40 : }
      32                 :            : 
      33                 :            : /*
      34                 :            :  *= https://www.rfc-editor.org/rfc/rfc8446#section-4.2.2
      35                 :            :  *#   struct {
      36                 :            :  *#       opaque cookie<1..2^16-1>;
      37                 :            :  *#   } Cookie;
      38                 :            :  */
      39                 :            : int s2n_cookie_send(struct s2n_connection *conn, struct s2n_stuffer *out)
      40                 :         85 : {
      41 [ #  # ][ -  + ]:         85 :     POSIX_ENSURE_REF(conn);
      42                 :            : 
      43         [ -  + ]:         85 :     POSIX_GUARD(s2n_stuffer_write_uint16(out, conn->cookie.size));
      44         [ -  + ]:         85 :     POSIX_GUARD(s2n_stuffer_write(out, &conn->cookie));
      45                 :            : 
      46                 :         85 :     return S2N_SUCCESS;
      47                 :         85 : }
      48                 :            : 
      49                 :            : /*
      50                 :            :  * Our server does not send cookies in production, so
      51                 :            :  * should never receive a cookie back from the client.
      52                 :            :  *
      53                 :            :  * However, we may enable cookies for testing.
      54                 :            :  * In that case, verify the proper client behavior by
      55                 :            :  * checking that the cookie sent matches the cookie received.
      56                 :            :  * This is also why the "if_missing" behavior is an error.
      57                 :            :  */
      58                 :            : static int s2n_client_cookie_recv(struct s2n_connection *conn, struct s2n_stuffer *extension)
      59                 :         52 : {
      60 [ -  + ][ #  # ]:         52 :     POSIX_ENSURE_REF(conn);
      61 [ -  + ][ #  # ]:         52 :     POSIX_ENSURE(s2n_in_unit_test(), S2N_ERR_UNSUPPORTED_EXTENSION);
      62                 :            : 
      63                 :         52 :     uint16_t size = 0;
      64         [ -  + ]:         52 :     POSIX_GUARD(s2n_stuffer_read_uint16(extension, &size));
      65 [ +  + ][ +  - ]:         52 :     POSIX_ENSURE(size == conn->cookie.size, S2N_ERR_BAD_MESSAGE);
      66 [ -  + ][ #  # ]:         47 :     POSIX_ENSURE(size >= s2n_stuffer_data_available(extension), S2N_ERR_BAD_MESSAGE);
      67                 :            : 
      68                 :         47 :     uint8_t *cookie = s2n_stuffer_raw_read(extension, size);
      69 [ -  + ][ #  # ]:         47 :     POSIX_ENSURE_REF(cookie);
      70 [ +  + ][ +  - ]:         47 :     POSIX_ENSURE(s2n_constant_time_equals(cookie, conn->cookie.data, size), S2N_ERR_BAD_MESSAGE);
      71                 :            : 
      72                 :         42 :     return S2N_SUCCESS;
      73                 :         47 : }
      74                 :            : 
      75                 :            : const s2n_extension_type s2n_client_cookie_extension = {
      76                 :            :     .iana_value = TLS_EXTENSION_COOKIE,
      77                 :            :     .minimum_version = S2N_TLS13,
      78                 :            :     .is_response = true,
      79                 :            :     .send = s2n_cookie_send,
      80                 :            :     .recv = s2n_client_cookie_recv,
      81                 :            :     .should_send = s2n_client_cookie_should_send,
      82                 :            :     .if_missing = s2n_extension_error_if_missing,
      83                 :            : };