File: kex.c

package info (click to toggle)
libssh 0.6.3-4
  • links: PTS, VCS
  • area: main
  • in suites: jessie-kfreebsd
  • size: 2,824 kB
  • sloc: ansic: 38,301; cpp: 372; makefile: 40; sh: 22; python: 9
file content (560 lines) | stat: -rw-r--r-- 15,971 bytes parent folder | download | duplicates (2)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
/*
 * kex.c - key exchange
 *
 * This file is part of the SSH Library
 *
 * Copyright (c) 2003-2008 by Aris Adamantiadis
 *
 * The SSH Library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or (at your
 * option) any later version.
 *
 * The SSH Library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with the SSH Library; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

#include "config.h"

#include <string.h>
#include <stdlib.h>
#include <stdio.h>

#include "libssh/priv.h"
#include "libssh/buffer.h"
#include "libssh/dh.h"
#include "libssh/kex.h"
#include "libssh/session.h"
#include "libssh/ssh2.h"
#include "libssh/string.h"
#include "libssh/curve25519.h"
#include "libssh/knownhosts.h"

#ifdef HAVE_LIBGCRYPT
# define BLOWFISH "blowfish-cbc,"
# define AES "aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,"
# define DES "3des-cbc,des-cbc-ssh1"
#elif defined(HAVE_LIBCRYPTO)
# ifdef HAVE_OPENSSL_BLOWFISH_H
#  define BLOWFISH "blowfish-cbc,"
# else
#  define BLOWFISH ""
# endif
# ifdef HAVE_OPENSSL_AES_H
#  ifdef BROKEN_AES_CTR
#   define AES "aes256-cbc,aes192-cbc,aes128-cbc,"
#  else
#   define AES "aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,"
#  endif /* BROKEN_AES_CTR */
# else
#  define AES ""
#  endif
# define DES "3des-cbc,des-cbc-ssh1"
#endif

#ifdef WITH_ZLIB
#define ZLIB "none,zlib,zlib@openssh.com"
#else
#define ZLIB "none"
#endif

#ifdef HAVE_CURVE25519
#define CURVE25519 "curve25519-sha256@libssh.org,"
#else
#define CURVE25519 ""
#endif

#ifdef HAVE_ECDH
#define ECDH "ecdh-sha2-nistp256,"
#define HOSTKEYS "ecdsa-sha2-nistp256,ssh-rsa,ssh-dss"
#else
#define HOSTKEYS "ssh-rsa,ssh-dss"
#define ECDH ""
#endif

#define KEY_EXCHANGE CURVE25519 ECDH "diffie-hellman-group14-sha1,diffie-hellman-group1-sha1"
#define KEX_METHODS_SIZE 10

/* NOTE: This is a fixed API and the index is defined by ssh_kex_types_e */
static const char *default_methods[] = {
  KEY_EXCHANGE,
  HOSTKEYS,
  AES BLOWFISH DES,
  AES BLOWFISH DES,
  "hmac-sha1",
  "hmac-sha1",
  "none",
  "none",
  "",
  "",
  NULL
};

/* NOTE: This is a fixed API and the index is defined by ssh_kex_types_e */
static const char *supported_methods[] = {
  KEY_EXCHANGE,
  HOSTKEYS,
  AES BLOWFISH DES,
  AES BLOWFISH DES,
  "hmac-sha1",
  "hmac-sha1",
  ZLIB,
  ZLIB,
  "",
  "",
  NULL
};

/* descriptions of the key exchange packet */
static const char *ssh_kex_descriptions[] = {
  "kex algos",
  "server host key algo",
  "encryption client->server",
  "encryption server->client",
  "mac algo client->server",
  "mac algo server->client",
  "compression algo client->server",
  "compression algo server->client",
  "languages client->server",
  "languages server->client",
  NULL
};

/* tokenize will return a token of strings delimited by ",". the first element has to be freed */
static char **tokenize(const char *chain){
    char **tokens;
    int n=1;
    int i=0;
    char *tmp;
    char *ptr;

    tmp = strdup(chain);
    if (tmp == NULL) {
      return NULL;
    }
    ptr = tmp;
    while(*ptr){
        if(*ptr==','){
            n++;
            *ptr=0;
        }
        ptr++;
    }
    /* now n contains the number of tokens, the first possibly empty if the list was empty too e.g. "" */
    tokens=malloc(sizeof(char *) * (n+1) ); /* +1 for the null */
    if (tokens == NULL) {
      SAFE_FREE(tmp);
      return NULL;
    }
    ptr=tmp;
    for(i=0;i<n;i++){
        tokens[i]=ptr;
        while(*ptr)
            ptr++; // find a zero
        ptr++; // then go one step further
    }
    tokens[i]=NULL;
    return tokens;
}

/* same as tokenize(), but with spaces instead of ',' */
/* TODO FIXME rewrite me! */
char **space_tokenize(const char *chain){
    char **tokens;
    int n=1;
    int i=0;
    char *tmp;
    char *ptr;

    tmp = strdup(chain);
    if (tmp == NULL) {
      return NULL;
    }
    ptr = tmp;

    while(*ptr==' ')
        ++ptr; /* skip initial spaces */
    while(*ptr){
        if(*ptr==' '){
            n++; /* count one token per word */
            *ptr=0;
            while(*(ptr+1)==' '){ /* don't count if the tokens have more than 2 spaces */
                *(ptr++)=0;
            }
        }
        ptr++;
    }
    /* now n contains the number of tokens, the first possibly empty if the list was empty too e.g. "" */
    tokens = malloc(sizeof(char *) * (n + 1)); /* +1 for the null */
    if (tokens == NULL) {
      SAFE_FREE(tmp);
      return NULL;
    }
    ptr=tmp; /* we don't pass the initial spaces because the "tmp" pointer is needed by the caller */
                    /* function to free the tokens. */
    for(i=0;i<n;i++){
        tokens[i]=ptr;
        if(i!=n-1){
            while(*ptr)
                ptr++; // find a zero
            while(!*(ptr+1))
                ++ptr; /* if the zero is followed by other zeros, go through them */
            ptr++; // then go one step further
        }
    }
    tokens[i]=NULL;
    return tokens;
}

const char *ssh_kex_get_supported_method(uint32_t algo) {
  if (algo >= KEX_METHODS_SIZE) {
    return NULL;
  }

  return supported_methods[algo];
}

const char *ssh_kex_get_description(uint32_t algo) {
  if (algo >= KEX_METHODS_SIZE) {
    return NULL;
  }

  return ssh_kex_descriptions[algo];
}

/* find_matching gets 2 parameters : a list of available objects (available_d), separated by colons,*/
/* and a list of preferred objects (preferred_d) */
/* it will return a strduped pointer on the first preferred object found in the available objects list */

char *ssh_find_matching(const char *available_d, const char *preferred_d){
    char ** tok_available, **tok_preferred;
    int i_avail, i_pref;
    char *ret;

    if ((available_d == NULL) || (preferred_d == NULL)) {
      return NULL; /* don't deal with null args */
    }

    tok_available = tokenize(available_d);
    if (tok_available == NULL) {
      return NULL;
    }

    tok_preferred = tokenize(preferred_d);
    if (tok_preferred == NULL) {
      SAFE_FREE(tok_available[0]);
      SAFE_FREE(tok_available);
      return NULL;
    }

    for(i_pref=0; tok_preferred[i_pref] ; ++i_pref){
      for(i_avail=0; tok_available[i_avail]; ++i_avail){
        if(strcmp(tok_available[i_avail],tok_preferred[i_pref]) == 0){
          /* match */
          ret=strdup(tok_available[i_avail]);
          /* free the tokens */
          SAFE_FREE(tok_available[0]);
          SAFE_FREE(tok_preferred[0]);
          SAFE_FREE(tok_available);
          SAFE_FREE(tok_preferred);
          return ret;
        }
      }
    }
    SAFE_FREE(tok_available[0]);
    SAFE_FREE(tok_preferred[0]);
    SAFE_FREE(tok_available);
    SAFE_FREE(tok_preferred);
    return NULL;
}

SSH_PACKET_CALLBACK(ssh_packet_kexinit){
	int server_kex=session->server;
  ssh_string str = NULL;
  char *strings[KEX_METHODS_SIZE];
  int i;

  (void)type;
  (void)user;
  memset(strings, 0, sizeof(strings));
  if (session->session_state == SSH_SESSION_STATE_AUTHENTICATED){
      SSH_LOG(SSH_LOG_WARNING, "Other side initiating key re-exchange");
  } else if(session->session_state != SSH_SESSION_STATE_INITIAL_KEX){
  	ssh_set_error(session,SSH_FATAL,"SSH_KEXINIT received in wrong state");
  	goto error;
  }
  if (server_kex) {
      if (buffer_get_data(packet,session->next_crypto->client_kex.cookie,16) != 16) {
        ssh_set_error(session, SSH_FATAL, "ssh_packet_kexinit: no cookie in packet");
        goto error;
      }

      if (hashbufin_add_cookie(session, session->next_crypto->client_kex.cookie) < 0) {
        ssh_set_error(session, SSH_FATAL, "ssh_packet_kexinit: adding cookie failed");
        goto error;
      }
  } else {
      if (buffer_get_data(packet,session->next_crypto->server_kex.cookie,16) != 16) {
        ssh_set_error(session, SSH_FATAL, "ssh_packet_kexinit: no cookie in packet");
        goto error;
      }

      if (hashbufin_add_cookie(session, session->next_crypto->server_kex.cookie) < 0) {
        ssh_set_error(session, SSH_FATAL, "ssh_packet_kexinit: adding cookie failed");
        goto error;
      }
  }

  for (i = 0; i < KEX_METHODS_SIZE; i++) {
    str = buffer_get_ssh_string(packet);
    if (str == NULL) {
      goto error;
    }

    if (buffer_add_ssh_string(session->in_hashbuf, str) < 0) {
    	ssh_set_error(session, SSH_FATAL, "Error adding string in hash buffer");
      goto error;
    }

    strings[i] = ssh_string_to_char(str);
    if (strings[i] == NULL) {
    	ssh_set_error_oom(session);
      goto error;
    }
    ssh_string_free(str);
    str = NULL;
  }

  /* copy the server kex info into an array of strings */
  if (server_kex) {
    for (i = 0; i < SSH_KEX_METHODS; i++) {
      session->next_crypto->client_kex.methods[i] = strings[i];
    }
  } else { /* client */
    for (i = 0; i < SSH_KEX_METHODS; i++) {
      session->next_crypto->server_kex.methods[i] = strings[i];
    }
  }

  session->session_state=SSH_SESSION_STATE_KEXINIT_RECEIVED;
  session->dh_handshake_state=DH_STATE_INIT;
  session->ssh_connection_callback(session);
  return SSH_PACKET_USED;
error:
  ssh_string_free(str);
  for (i = 0; i < SSH_KEX_METHODS; i++) {
    if (server_kex) {
        session->next_crypto->client_kex.methods[i] = NULL;
    } else { /* client */
        session->next_crypto->server_kex.methods[i] = NULL;
    }
    SAFE_FREE(strings[i]);
  }

  session->session_state = SSH_SESSION_STATE_ERROR;

  return SSH_PACKET_USED;
}

void ssh_list_kex(struct ssh_kex_struct *kex) {
  int i = 0;

#ifdef DEBUG_CRYPTO
  ssh_print_hexa("session cookie", kex->cookie, 16);
#endif

  for(i = 0; i < SSH_KEX_METHODS; i++) {
    if (kex->methods[i] == NULL) {
      continue;
    }
    SSH_LOG(SSH_LOG_FUNCTIONS, "%s: %s",
        ssh_kex_descriptions[i], kex->methods[i]);
  }
}

/**
 * @internal
 * @brief selects the hostkey mechanisms to be chosen for the key exchange,
 * as some hostkey mechanisms may be present in known_hosts file and preferred
 * @returns a cstring containing a comma-separated list of hostkey methods.
 *          NULL if no method matches
 */
static char *ssh_client_select_hostkeys(ssh_session session){
    char methods_buffer[128]={0};
    static const char *preferred_hostkeys[]={"ecdsa-sha2-nistp521","ecdsa-sha2-nistp384",
    		"ecdsa-sha2-nistp256", "ssh-rsa", "ssh-dss", "ssh-rsa1", NULL};
    char **methods;
    int i,j;
    int needcoma=0;

    methods = ssh_knownhosts_algorithms(session);
	if (methods == NULL || methods[0] == NULL){
		SAFE_FREE(methods);
		return NULL;
	}

	for (i=0;preferred_hostkeys[i] != NULL; ++i){
		for (j=0; methods[j] != NULL; ++j){
			if(strcmp(preferred_hostkeys[i], methods[j]) == 0){
				if (verify_existing_algo(SSH_HOSTKEYS, methods[j])){
					if(needcoma)
						strncat(methods_buffer,",",sizeof(methods_buffer)-strlen(methods_buffer)-1);
					strncat(methods_buffer, methods[j], sizeof(methods_buffer)-strlen(methods_buffer)-1);
					needcoma = 1;
				}
			}
		}
	}
	for(i=0;methods[i]!= NULL; ++i){
		SAFE_FREE(methods[i]);
	}
	SAFE_FREE(methods);

	if(strlen(methods_buffer) > 0){
		SSH_LOG(SSH_LOG_DEBUG, "Changing host key method to \"%s\"", methods_buffer);
		return strdup(methods_buffer);
	} else {
		SSH_LOG(SSH_LOG_DEBUG, "No supported kex method for existing key in known_hosts file");
		return NULL;
	}

}
/**
 * @brief sets the key exchange parameters to be sent to the server,
 *        in function of the options and available methods.
 */
int set_client_kex(ssh_session session){
    struct ssh_kex_struct *client= &session->next_crypto->client_kex;
    const char *wanted;
    int i;

    ssh_get_random(client->cookie, 16, 0);

    memset(client->methods, 0, KEX_METHODS_SIZE * sizeof(char **));
    /* first check if we have specific host key methods */
    if(session->opts.wanted_methods[SSH_HOSTKEYS] == NULL){
    	/* Only if no override */
    	session->opts.wanted_methods[SSH_HOSTKEYS] =
    			ssh_client_select_hostkeys(session);
    }

    for (i = 0; i < KEX_METHODS_SIZE; i++) {
        wanted = session->opts.wanted_methods[i];
        if (wanted == NULL)
            wanted = default_methods[i];
        client->methods[i] = strdup(wanted);
    }

    return SSH_OK;
}

/** @brief Select the different methods on basis of client's and
 * server's kex messages, and watches out if a match is possible.
 */
int ssh_kex_select_methods (ssh_session session){
    struct ssh_kex_struct *server = &session->next_crypto->server_kex;
    struct ssh_kex_struct *client = &session->next_crypto->client_kex;
    int i;

    for (i = 0; i < KEX_METHODS_SIZE; i++) {
        session->next_crypto->kex_methods[i]=ssh_find_matching(server->methods[i],client->methods[i]);
        if(session->next_crypto->kex_methods[i] == NULL && i < SSH_LANG_C_S){
            ssh_set_error(session,SSH_FATAL,"kex error : no match for method %s: server [%s], client [%s]",
                    ssh_kex_descriptions[i],server->methods[i],client->methods[i]);
            return SSH_ERROR;
        } else if ((i >= SSH_LANG_C_S) && (session->next_crypto->kex_methods[i] == NULL)) {
            /* we can safely do that for languages */
            session->next_crypto->kex_methods[i] = strdup("");
        }
    }
    if(strcmp(session->next_crypto->kex_methods[SSH_KEX], "diffie-hellman-group1-sha1") == 0){
      session->next_crypto->kex_type=SSH_KEX_DH_GROUP1_SHA1;
    } else if(strcmp(session->next_crypto->kex_methods[SSH_KEX], "diffie-hellman-group14-sha1") == 0){
      session->next_crypto->kex_type=SSH_KEX_DH_GROUP14_SHA1;
    } else if(strcmp(session->next_crypto->kex_methods[SSH_KEX], "ecdh-sha2-nistp256") == 0){
      session->next_crypto->kex_type=SSH_KEX_ECDH_SHA2_NISTP256;
    } else if(strcmp(session->next_crypto->kex_methods[SSH_KEX], "curve25519-sha256@libssh.org") == 0){
      session->next_crypto->kex_type=SSH_KEX_CURVE25519_SHA256_LIBSSH_ORG;
    }

    return SSH_OK;
}


/* this function only sends the predefined set of kex methods */
int ssh_send_kex(ssh_session session, int server_kex) {
  struct ssh_kex_struct *kex = (server_kex ? &session->next_crypto->server_kex :
      &session->next_crypto->client_kex);
  ssh_string str = NULL;
  int i;

  if (buffer_add_u8(session->out_buffer, SSH2_MSG_KEXINIT) < 0) {
    goto error;
  }
  if (buffer_add_data(session->out_buffer, kex->cookie, 16) < 0) {
    goto error;
  }

  if (hashbufout_add_cookie(session) < 0) {
    goto error;
  }

  ssh_list_kex(kex);

  for (i = 0; i < KEX_METHODS_SIZE; i++) {
    str = ssh_string_from_char(kex->methods[i]);
    if (str == NULL) {
      goto error;
    }

    if (buffer_add_ssh_string(session->out_hashbuf, str) < 0) {
      goto error;
    }
    if (buffer_add_ssh_string(session->out_buffer, str) < 0) {
      goto error;
    }
    ssh_string_free(str);
    str = NULL;
  }

  if (buffer_add_u8(session->out_buffer, 0) < 0) {
    goto error;
  }
  if (buffer_add_u32(session->out_buffer, 0) < 0) {
    goto error;
  }

  if (packet_send(session) == SSH_ERROR) {
    return -1;
  }

  return 0;
error:
  buffer_reinit(session->out_buffer);
  buffer_reinit(session->out_hashbuf);
  ssh_string_free(str);

  return -1;
}

/* returns 1 if at least one of the name algos is in the default algorithms table */
int verify_existing_algo(int algo, const char *name){
    char *ptr;
    if(algo>9 || algo <0)
        return -1;
    ptr=ssh_find_matching(supported_methods[algo],name);
    if(ptr){
        free(ptr);
        return 1;
    }
    return 0;
}

/* vim: set ts=2 sw=2 et cindent: */