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Tree: 63a83cf0416ab89720b15a4a649786812b630b79

Files: 63a83cf0416ab89720b15a4a649786812b630b79 / tls.c

10330 bytesRaw
1/*
2 * Copyright (c) 2011 and 2012, Dustin Lundquist <dustin@null-ptr.net>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are met:
7 *
8 * 1. Redistributions of source code must retain the above copyright notice,
9 *    this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
15 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
18 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
19 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
20 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
21 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
22 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
23 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
24 * POSSIBILITY OF SUCH DAMAGE.
25 */
26/*
27 * This is a minimal TLS implementation intended only to parse the server name
28 * extension.  This was created based primarily on Wireshark dissection of a
29 * TLS handshake and RFC4366.
30 */
31#include <stdio.h>
32#include <stdlib.h> /* malloc() */
33#include "tls.h"
34
35#define TLS_HEADER_LEN 5
36#define TLS_HANDSHAKE_CONTENT_TYPE 0x16
37#define TLS_HANDSHAKE_TYPE_CLIENT_HELLO 0x01
38
39#ifndef MIN
40#define MIN(X, Y) ((X) < (Y) ? (X) : (Y))
41#endif
42
43
44struct TLSProtocol {
45    int use_alpn;
46    char** sni_hostname_list;
47    char** alpn_protocol_list;
48};
49
50static int parse_extensions(const struct TLSProtocol *, const char *, size_t);
51static int parse_server_name_extension(const struct TLSProtocol *, const char *, size_t);
52static int parse_alpn_extension(const struct TLSProtocol *, const char *, size_t);
53static int has_match(char**, const char*, size_t);
54
55/* Parse a TLS packet for the Server Name Indication and ALPN extension in the client
56 * hello handshake, returning a status code
57 *
58 * Returns:
59 *  >=0  - length of the hostname and updates *hostname
60 *         caller is responsible for freeing *hostname
61 *  -1   - Incomplete request
62 *  -2   - No Host header included in this request
63 *  -3   - Invalid hostname pointer
64 *  < -4 - Invalid TLS client hello
65 */
66int
67parse_tls_header(const struct TLSProtocol *tls_data, const char *data, size_t data_len) {
68    char tls_content_type;
69    char tls_version_major;
70    char tls_version_minor;
71    size_t pos = TLS_HEADER_LEN;
72    size_t len;
73
74    /* Check that our TCP payload is at least large enough for a TLS header */
75    if (data_len < TLS_HEADER_LEN)
76        return -1;
77
78    tls_content_type = data[0];
79    if (tls_content_type != TLS_HANDSHAKE_CONTENT_TYPE) {
80        if (verbose) fprintf(stderr, "Request did not begin with TLS handshake.\n");
81        return -5;
82    }
83
84    tls_version_major = data[1];
85    tls_version_minor = data[2];
86    if (tls_version_major < 3) {
87        if (verbose) fprintf(stderr, "Received SSL %d.%d handshake which cannot be parsed.\n",
88              tls_version_major, tls_version_minor);
89
90        return -2;
91    }
92
93    /* TLS record length */
94    len = ((unsigned char)data[3] << 8) +
95          (unsigned char)data[4] + TLS_HEADER_LEN;
96    data_len = MIN(data_len, len);
97
98    /* Check we received entire TLS record length */
99    if (data_len < len)
100        return -1;
101
102    /*
103     * Handshake
104     */
105    if (pos + 1 > data_len) {
106        return -5;
107    }
108    if (data[pos] != TLS_HANDSHAKE_TYPE_CLIENT_HELLO) {
109        if (verbose) fprintf(stderr, "Not a client hello\n");
110
111        return -5;
112    }
113
114    /* Skip past fixed length records:
115       1	Handshake Type
116       3	Length
117       2	Version (again)
118       32	Random
119       to	Session ID Length
120     */
121    pos += 38;
122
123    /* Session ID */
124    if (pos + 1 > data_len)
125        return -5;
126    len = (unsigned char)data[pos];
127    pos += 1 + len;
128
129    /* Cipher Suites */
130    if (pos + 2 > data_len)
131        return -5;
132    len = ((unsigned char)data[pos] << 8) + (unsigned char)data[pos + 1];
133    pos += 2 + len;
134
135    /* Compression Methods */
136    if (pos + 1 > data_len)
137        return -5;
138    len = (unsigned char)data[pos];
139    pos += 1 + len;
140
141    if (pos == data_len && tls_version_major == 3 && tls_version_minor == 0) {
142        if (verbose) fprintf(stderr, "Received SSL 3.0 handshake without extensions\n");
143        return -2;
144    }
145
146    /* Extensions */
147    if (pos + 2 > data_len)
148        return -5;
149    len = ((unsigned char)data[pos] << 8) + (unsigned char)data[pos + 1];
150    pos += 2;
151
152    if (pos + len > data_len)
153        return -5;
154    return parse_extensions(tls_data, data + pos, len);
155}
156
157static int
158parse_extensions(const struct TLSProtocol *tls_data, const char *data, size_t data_len) {
159    size_t pos = 0;
160    size_t len;
161    int last_matched = 0;
162
163    if (tls_data == NULL)
164        return -3;
165
166    /* Parse each 4 bytes for the extension header */
167    while (pos + 4 <= data_len) {
168        /* Extension Length */
169        len = ((unsigned char) data[pos + 2] << 8) +
170              (unsigned char) data[pos + 3];
171
172        if (pos + 4 + len > data_len)
173            return -5;
174
175        size_t extension_type = ((unsigned char) data[pos] << 8) +
176                                (unsigned char) data[pos + 1];
177
178
179        /* Check if it's a server name extension */
180        /* There can be only one extension of each type, so we break
181           our state and move pos to beginning of the extension here */
182        if (tls_data->use_alpn == 2) {
183            /* we want BOTH alpn and sni to match */
184            if (extension_type == 0x00) { /* Server Name */
185                if (parse_server_name_extension(tls_data, data + pos + 4, len)) {
186                    /* SNI matched */
187                    if(last_matched) {
188                        /* this is only true if ALPN matched, so return true */
189                        return last_matched;
190                    } else {
191                        /* otherwise store that SNI matched */
192                        last_matched = 1;
193                    }
194                } else {
195                    // both can't match
196                    return -2;
197                }
198            } else if (extension_type == 0x10) { /* ALPN */
199                if (parse_alpn_extension(tls_data, data + pos + 4, len)) {
200                    /* ALPN matched */
201                    if(last_matched) {
202                        /* this is only true if SNI matched, so return true */
203                        return last_matched;
204                    } else {
205                        /* otherwise store that ALPN matched */
206                        last_matched = 1;
207                    }
208                } else {
209                    // both can't match
210                    return -2;
211                }
212            }
213
214        } else if (extension_type == 0x00 && tls_data->use_alpn == 0) { /* Server Name */
215            return parse_server_name_extension(tls_data, data + pos + 4, len);
216        } else if (extension_type == 0x10 && tls_data->use_alpn == 1) { /* ALPN */
217            return parse_alpn_extension(tls_data, data + pos + 4, len);
218        }
219
220        pos += 4 + len; /* Advance to the next extension header */
221    }
222
223    /* Check we ended where we expected to */
224    if (pos != data_len)
225        return -5;
226
227    return -2;
228}
229
230static int
231parse_server_name_extension(const struct TLSProtocol *tls_data, const char *data, size_t data_len) {
232    size_t pos = 2; /* skip server name list length */
233    size_t len;
234
235    while (pos + 3 < data_len) {
236        len = ((unsigned char)data[pos + 1] << 8) +
237              (unsigned char)data[pos + 2];
238
239        if (pos + 3 + len > data_len)
240            return -5;
241
242        switch (data[pos]) { /* name type */
243            case 0x00: /* host_name */
244                if(has_match(tls_data->sni_hostname_list, data + pos + 3, len)) {
245                    return len;
246                } else {
247                    return -2;
248                }
249            default:
250                if (verbose) fprintf(stderr, "Unknown server name extension name type: %d\n",
251                      data[pos]);
252        }
253        pos += 3 + len;
254    }
255    /* Check we ended where we expected to */
256    if (pos != data_len)
257        return -5;
258
259    return -2;
260}
261
262static int
263parse_alpn_extension(const struct TLSProtocol *tls_data, const char *data, size_t data_len) {
264    size_t pos = 2;
265    size_t len;
266
267    while (pos + 1 < data_len) {
268        len = (unsigned char)data[pos];
269
270        if (pos + 1 + len > data_len)
271            return -5;
272
273        if (len > 0 && has_match(tls_data->alpn_protocol_list, data + pos + 1, len)) {
274            return len;
275        } else if (len > 0) {
276            if (verbose) fprintf(stderr, "Unknown ALPN name: %.*s\n", (int)len, data + pos + 1);
277        }
278        pos += 1 + len;
279    }
280    /* Check we ended where we expected to */
281    if (pos != data_len)
282        return -5;
283
284    return -2;
285}
286
287static int
288has_match(char** list, const char* name, size_t name_len) {
289    char **item;
290
291    for (item = list; *item; item++) {
292        if (verbose) fprintf(stderr, "matching [%.*s] with [%s]\n", (int)name_len, name, *item);
293        if(!strncmp(*item, name, name_len)) {
294            return 1;
295        }
296    }
297    return 0;
298}
299
300struct TLSProtocol *
301new_tls_data() {
302    struct TLSProtocol *tls_data = malloc(sizeof(struct TLSProtocol));
303    if (tls_data != NULL) {
304        tls_data->use_alpn = -1;
305    }
306
307    return tls_data;
308}
309
310struct TLSProtocol *
311tls_data_set_list(struct TLSProtocol *tls_data, int alpn, char** list) {
312    if (alpn) {
313        tls_data->alpn_protocol_list = list;
314        if(tls_data->use_alpn == 0)
315            tls_data->use_alpn = 2;
316        else
317            tls_data->use_alpn = 1;
318    } else {
319        tls_data->sni_hostname_list = list;
320        if(tls_data->use_alpn == 1)
321            tls_data->use_alpn = 2;
322        else
323            tls_data->use_alpn = 0;
324    }
325
326    return tls_data;
327}
328

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