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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_client_max_frag_len.h"
      17                 :            : 
      18                 :            : #include <stdint.h>
      19                 :            : 
      20                 :            : #include "tls/s2n_tls.h"
      21                 :            : #include "tls/s2n_tls_parameters.h"
      22                 :            : #include "utils/s2n_safety.h"
      23                 :            : 
      24                 :            : static bool s2n_client_max_frag_len_should_send(struct s2n_connection *conn);
      25                 :            : static int s2n_client_max_frag_len_send(struct s2n_connection *conn, struct s2n_stuffer *out);
      26                 :            : static int s2n_client_max_frag_len_recv(struct s2n_connection *conn, struct s2n_stuffer *extension);
      27                 :            : 
      28                 :            : const s2n_extension_type s2n_client_max_frag_len_extension = {
      29                 :            :     .iana_value = TLS_EXTENSION_MAX_FRAG_LEN,
      30                 :            :     .is_response = false,
      31                 :            :     .send = s2n_client_max_frag_len_send,
      32                 :            :     .recv = s2n_client_max_frag_len_recv,
      33                 :            :     .should_send = s2n_client_max_frag_len_should_send,
      34                 :            :     .if_missing = s2n_extension_noop_if_missing,
      35                 :            : };
      36                 :            : 
      37                 :            : static bool s2n_client_max_frag_len_should_send(struct s2n_connection *conn)
      38                 :       7723 : {
      39                 :       7723 :     return conn->config->mfl_code != S2N_TLS_MAX_FRAG_LEN_EXT_NONE;
      40                 :       7723 : }
      41                 :            : 
      42                 :            : static int s2n_client_max_frag_len_send(struct s2n_connection *conn, struct s2n_stuffer *out)
      43                 :        393 : {
      44                 :        393 :     return s2n_stuffer_write_uint8(out, conn->config->mfl_code);
      45                 :        393 : }
      46                 :            : 
      47                 :            : static int s2n_client_max_frag_len_recv(struct s2n_connection *conn, struct s2n_stuffer *extension)
      48                 :        392 : {
      49         [ +  + ]:        392 :     if (!conn->config->accept_mfl) {
      50                 :          6 :         return S2N_SUCCESS;
      51                 :          6 :     }
      52                 :            : 
      53                 :        386 :     uint8_t mfl_code = 0;
      54         [ -  + ]:        386 :     POSIX_GUARD(s2n_stuffer_read_uint8(extension, &mfl_code));
      55                 :            : 
      56                 :            :     /*
      57                 :            :      *= https://www.rfc-editor.org/rfc/rfc6066#section-4
      58                 :            :      *= type=exception
      59                 :            :      *= reason=For compatibility, we choose to ignore malformed extensions if they are optional
      60                 :            :      *# If a server receives a maximum fragment length negotiation request
      61                 :            :      *# for a value other than the allowed values, it MUST abort the
      62                 :            :      *# handshake with an "illegal_parameter" alert.
      63                 :            :      */
      64 [ +  + ][ -  + ]:        386 :     if (mfl_code >= s2n_array_len(mfl_code_to_length) || mfl_code_to_length[mfl_code] > S2N_TLS_MAXIMUM_FRAGMENT_LENGTH) {
      65                 :          1 :         return S2N_SUCCESS;
      66                 :          1 :     }
      67                 :            : 
      68                 :            :     /*
      69                 :            :      *= https://www.rfc-editor.org/rfc/rfc6066#section-4
      70                 :            :      *# Once a maximum fragment length other than 2^14 has been successfully
      71                 :            :      *# negotiated, the client and server MUST immediately begin fragmenting
      72                 :            :      *# messages (including handshake messages) to ensure that no fragment
      73                 :            :      *# larger than the negotiated length is sent.
      74                 :            :      */
      75                 :        385 :     conn->negotiated_mfl_code = mfl_code;
      76         [ -  + ]:        385 :     POSIX_GUARD_RESULT(s2n_connection_set_max_fragment_length(conn, mfl_code_to_length[mfl_code]));
      77                 :        385 :     return S2N_SUCCESS;
      78                 :        385 : }