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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_server_supported_versions.h"
      17                 :            : 
      18                 :            : #include <stdint.h>
      19                 :            : 
      20                 :            : #include "tls/extensions/s2n_supported_versions.h"
      21                 :            : #include "tls/s2n_alerts.h"
      22                 :            : #include "tls/s2n_cipher_preferences.h"
      23                 :            : #include "tls/s2n_tls.h"
      24                 :            : #include "tls/s2n_tls_parameters.h"
      25                 :            : #include "utils/s2n_safety.h"
      26                 :            : 
      27                 :            : /**
      28                 :            :  * Specified in https://tools.ietf.org/html/rfc8446#section-4.2.1
      29                 :            :  *
      30                 :            :  * "A server which negotiates TLS 1.3 MUST respond by sending a
      31                 :            :  * "supported_versions" extension containing the selected version value
      32                 :            :  * (0x0304)."
      33                 :            :  *
      34                 :            :  * Structure:
      35                 :            :  * Extension type (2 bytes)
      36                 :            :  * Extension size (2 bytes)
      37                 :            :  * Selected Version (2 byte)
      38                 :            :  **/
      39                 :            : 
      40                 :            : static int s2n_server_supported_versions_send(struct s2n_connection *conn, struct s2n_stuffer *out);
      41                 :            : static int s2n_server_supported_versions_recv(struct s2n_connection *conn, struct s2n_stuffer *in);
      42                 :            : 
      43                 :            : const s2n_extension_type s2n_server_supported_versions_extension = {
      44                 :            :     .iana_value = TLS_EXTENSION_SUPPORTED_VERSIONS,
      45                 :            :     .is_response = true,
      46                 :            :     .send = s2n_server_supported_versions_send,
      47                 :            :     .recv = s2n_server_supported_versions_recv,
      48                 :            :     .should_send = s2n_extension_send_if_tls13_connection,
      49                 :            :     .if_missing = s2n_extension_noop_if_missing,
      50                 :            : };
      51                 :            : 
      52                 :            : static int s2n_server_supported_versions_send(struct s2n_connection *conn, struct s2n_stuffer *out)
      53                 :       5220 : {
      54         [ -  + ]:       5220 :     POSIX_GUARD(s2n_stuffer_write_uint8(out, conn->server_protocol_version / 10));
      55         [ -  + ]:       5220 :     POSIX_GUARD(s2n_stuffer_write_uint8(out, conn->server_protocol_version % 10));
      56                 :            : 
      57                 :       5220 :     return S2N_SUCCESS;
      58                 :       5220 : }
      59                 :            : 
      60                 :            : static int s2n_extensions_server_supported_versions_process(struct s2n_connection *conn, struct s2n_stuffer *extension)
      61                 :       5203 : {
      62                 :       5203 :     uint8_t highest_supported_version = conn->client_protocol_version;
      63                 :       5203 :     uint8_t minimum_supported_version = s2n_unknown_protocol_version;
      64         [ -  + ]:       5203 :     POSIX_GUARD_RESULT(s2n_connection_get_minimum_supported_version(conn, &minimum_supported_version));
      65 [ +  - ][ +  + ]:       5203 :     POSIX_ENSURE(highest_supported_version >= minimum_supported_version, S2N_ERR_PROTOCOL_VERSION_UNSUPPORTED);
      66                 :            : 
      67                 :       5202 :     uint8_t server_version_parts[S2N_TLS_PROTOCOL_VERSION_LEN];
      68         [ +  + ]:       5202 :     POSIX_GUARD(s2n_stuffer_read_bytes(extension, server_version_parts, S2N_TLS_PROTOCOL_VERSION_LEN));
      69                 :            : 
      70                 :       5200 :     uint16_t server_version = (server_version_parts[0] * 10) + server_version_parts[1];
      71                 :            : 
      72                 :            :     /**
      73                 :            :      *= https://www.rfc-editor.org/rfc/rfc8446#4.1.4
      74                 :            :      *# The value of selected_version in the HelloRetryRequest
      75                 :            :      *# "supported_versions" extension MUST be retained in the ServerHello,
      76                 :            :      *# and a client MUST abort the handshake with an "illegal_parameter"
      77                 :            :      *# alert if the value changes.
      78                 :            :      **/
      79 [ +  + ][ +  + ]:       5200 :     if (s2n_is_hello_retry_handshake(conn) && !s2n_is_hello_retry_message(conn)) {
      80 [ +  + ][ +  - ]:        640 :         POSIX_ENSURE(conn->server_protocol_version == server_version,
      81                 :        640 :                 S2N_ERR_BAD_MESSAGE);
      82                 :        640 :     }
      83                 :            : 
      84 [ +  - ][ +  + ]:       5199 :     POSIX_ENSURE_GTE(server_version, S2N_TLS13);
      85 [ +  + ][ +  - ]:       5198 :     POSIX_ENSURE_LTE(server_version, highest_supported_version);
      86 [ -  + ][ #  # ]:       5197 :     POSIX_ENSURE_GTE(server_version, minimum_supported_version);
      87                 :            : 
      88                 :       5197 :     conn->server_protocol_version = server_version;
      89                 :            : 
      90                 :       5197 :     return S2N_SUCCESS;
      91                 :       5197 : }
      92                 :            : 
      93                 :            : static int s2n_server_supported_versions_recv(struct s2n_connection *conn, struct s2n_stuffer *in)
      94                 :       5204 : {
      95         [ +  + ]:       5204 :     if (s2n_connection_get_protocol_version(conn) < S2N_TLS13) {
      96                 :          1 :         return S2N_SUCCESS;
      97                 :          1 :     }
      98                 :            : 
      99 [ +  + ][ +  - ]:       5203 :     S2N_ERROR_IF(s2n_extensions_server_supported_versions_process(conn, in) < 0, S2N_ERR_BAD_MESSAGE);
     100                 :       5197 :     return S2N_SUCCESS;
     101                 :       5203 : }
     102                 :            : 
     103                 :            : /* Old-style extension functions -- remove after extensions refactor is complete */
     104                 :            : 
     105                 :            : int s2n_extensions_server_supported_versions_size(struct s2n_connection *conn)
     106                 :          2 : {
     107                 :          2 :     return 6;
     108                 :          2 : }
     109                 :            : 
     110                 :            : int s2n_extensions_server_supported_versions_recv(struct s2n_connection *conn, struct s2n_stuffer *extension)
     111                 :          0 : {
     112                 :          0 :     return s2n_extension_recv(&s2n_server_supported_versions_extension, conn, extension);
     113                 :          0 : }