1 /*
2 * Copyright (C) 2018 Red Hat, Inc.
3 *
4 * Author: Daiki Ueno
5 *
6 * This file is part of GnuTLS.
7 *
8 * The GnuTLS is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU Lesser General Public License
10 * as published by the Free Software Foundation; either version 2.1 of
11 * the License, or (at your option) any later version.
12 *
13 * This library is distributed in the hope that it will be useful, but
14 * WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * Lesser General Public License for more details.
17 *
18 * You should have received a copy of the GNU Lesser General Public License
19 * along with this program. If not, see <https://www.gnu.org/licenses/>
20 *
21 */
22
23 /* This file contains the code for the Record Size Limit TLS extension.
24 */
25
26 #include "gnutls_int.h"
27 #include "errors.h"
28 #include "num.h"
29 #include <hello_ext.h>
30 #include <ext/record_size_limit.h>
31
32 static int _gnutls_record_size_limit_recv_params(gnutls_session_t session,
33 const uint8_t * data,
34 size_t data_size);
35 static int _gnutls_record_size_limit_send_params(gnutls_session_t session,
36 gnutls_buffer_st * extdata);
37
38 const hello_ext_entry_st ext_mod_record_size_limit = {
39 .name = "Record Size Limit",
40 .tls_id = 28,
41 .gid = GNUTLS_EXTENSION_RECORD_SIZE_LIMIT,
42 .client_parse_point = GNUTLS_EXT_MANDATORY,
43 .server_parse_point = GNUTLS_EXT_MANDATORY,
44 .validity = GNUTLS_EXT_FLAG_TLS | GNUTLS_EXT_FLAG_DTLS | GNUTLS_EXT_FLAG_CLIENT_HELLO |
45 GNUTLS_EXT_FLAG_EE | GNUTLS_EXT_FLAG_TLS12_SERVER_HELLO,
46 .recv_func = _gnutls_record_size_limit_recv_params,
47 .send_func = _gnutls_record_size_limit_send_params
48 };
49
50 static int
_gnutls_record_size_limit_recv_params(gnutls_session_t session,const uint8_t * data,size_t data_size)51 _gnutls_record_size_limit_recv_params(gnutls_session_t session,
52 const uint8_t * data, size_t data_size)
53 {
54 ssize_t new_size;
55 const version_entry_st *vers;
56
57 DECR_LEN(data_size, 2);
58 if (data_size != 0)
59 return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);
60 new_size = _gnutls_read_uint16(data);
61
62 /* protocol error */
63 if (new_size < 64)
64 return gnutls_assert_val(GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER);
65
66 session->internals.hsk_flags |= HSK_RECORD_SIZE_LIMIT_RECEIVED;
67
68 /* we do not want to accept sizes outside of our supported range */
69 if (new_size <
70 (session->internals.allow_small_records ?
71 MIN_RECORD_SIZE_SMALL : MIN_RECORD_SIZE)) {
72 /* for server, reject it by omitting the extension in the reply */
73 if (session->security_parameters.entity == GNUTLS_SERVER) {
74 _gnutls_handshake_log("EXT[%p]: client requested too small record_size_limit %u; ignoring\n",
75 session, (unsigned)new_size);
76 return gnutls_assert_val(0);
77 } else {
78 _gnutls_handshake_log("EXT[%p]: server requested too small record_size_limit %u; closing the connection\n",
79 session, (unsigned)new_size);
80 return gnutls_assert_val(GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER);
81 }
82 }
83
84 session->internals.hsk_flags |= HSK_RECORD_SIZE_LIMIT_NEGOTIATED;
85
86 /* client uses the reception of this extension as an
87 * indication of the request was accepted by the server */
88 if (session->security_parameters.entity == GNUTLS_CLIENT)
89 session->security_parameters.max_record_recv_size =
90 session->security_parameters.max_user_record_recv_size;
91
92 _gnutls_handshake_log("EXT[%p]: record_size_limit %u negotiated\n",
93 session, (unsigned)new_size);
94
95 /* subtract 1 octet for content type */
96 vers = get_version(session);
97 if (unlikely(vers == NULL))
98 return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
99
100 session->security_parameters.max_record_send_size =
101 MIN(new_size - vers->tls13_sem,
102 session->security_parameters.max_user_record_send_size);
103
104 return 0;
105 }
106
107 /* returns data_size or a negative number on failure
108 */
109 static int
_gnutls_record_size_limit_send_params(gnutls_session_t session,gnutls_buffer_st * extdata)110 _gnutls_record_size_limit_send_params(gnutls_session_t session,
111 gnutls_buffer_st * extdata)
112 {
113 int ret;
114 uint16_t send_size;
115
116 assert(session->security_parameters.max_user_record_recv_size >= 64 &&
117 session->security_parameters.max_user_record_recv_size <=
118 DEFAULT_MAX_RECORD_SIZE);
119
120 send_size = session->security_parameters.max_user_record_recv_size;
121
122 if (session->security_parameters.entity == GNUTLS_SERVER) {
123 const version_entry_st *vers;
124
125 /* if we had received the extension and rejected, don't send it */
126 if (session->internals.hsk_flags & HSK_RECORD_SIZE_LIMIT_RECEIVED &&
127 !(session->internals.hsk_flags & HSK_RECORD_SIZE_LIMIT_NEGOTIATED))
128 return gnutls_assert_val(0);
129
130 /* add 1 octet for content type */
131 vers = get_version(session);
132 if (unlikely(vers == NULL))
133 return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
134
135 session->security_parameters.max_record_recv_size =
136 send_size;
137
138 send_size += vers->tls13_sem;
139 } else {
140 const version_entry_st *vers;
141
142 /* add 1 octet for content type */
143 vers = _gnutls_version_max(session);
144 if (unlikely(vers == NULL))
145 return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
146
147 send_size += vers->tls13_sem;
148 }
149
150 ret = _gnutls_buffer_append_prefix(extdata, 16, send_size);
151 if (ret < 0)
152 return gnutls_assert_val(ret);
153
154 session->internals.hsk_flags |= HSK_RECORD_SIZE_LIMIT_SENT;
155
156 return 2;
157 }
158