summaryrefslogtreecommitdiff
path: root/src/openvpn/ssl_verify_mbedtls.c
blob: 42608235359157c4594e563a0b54c5693bf4afbf (plain)
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
/*
 *  OpenVPN -- An application to securely tunnel IP networks
 *             over a single TCP/UDP port, with support for SSL/TLS-based
 *             session authentication and key exchange,
 *             packet encryption, packet authentication, and
 *             packet compression.
 *
 *  Copyright (C) 2002-2010 OpenVPN Technologies, Inc. <sales@openvpn.net>
 *  Copyright (C) 2010 Fox Crypto B.V. <openvpn@fox-it.com>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2
 *  as published by the Free Software Foundation.
 *
 *  This program 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program (see the file COPYING included with this
 *  distribution); if not, write to the Free Software Foundation, Inc.,
 *  59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

/**
 * @file Control Channel Verification Module mbed TLS backend
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#elif defined(_MSC_VER)
#include "config-msvc.h"
#endif

#include "syshead.h"

#if defined(ENABLE_CRYPTO) && defined(ENABLE_CRYPTO_MBEDTLS)

#include "crypto_mbedtls.h"
#include "ssl_verify.h"
#include <mbedtls/asn1.h>
#include <mbedtls/error.h>
#include <mbedtls/bignum.h>
#include <mbedtls/oid.h>
#include <mbedtls/sha1.h>

#define MAX_SUBJECT_LENGTH 256

int
verify_callback (void *session_obj, mbedtls_x509_crt *cert, int cert_depth,
    uint32_t *flags)
{
  struct tls_session *session = (struct tls_session *) session_obj;
  struct gc_arena gc = gc_new();

  ASSERT (cert);
  ASSERT (session);

  session->verified = false;

  /* Remember certificate hash */
  struct buffer cert_fingerprint = x509_get_sha256_fingerprint (cert, &gc);
  cert_hash_remember (session, cert_depth, &cert_fingerprint);

  /* did peer present cert which was signed by our root cert? */
  if (*flags != 0)
    {
      int ret = 0;
      char errstr[512] = { 0 };
      char *subject = x509_get_subject(cert, &gc);

      ret = mbedtls_x509_crt_verify_info (errstr, sizeof(errstr)-1, "", *flags);
      if (ret <= 0 && !openvpn_snprintf(errstr, sizeof(errstr),
	    "Could not retrieve error string, flags=%"PRIx32, *flags))
	{
	  errstr[0] = '\0';
	}
      else
	{
	  chomp(errstr);
	}

      if (subject)
	{
	  msg (D_TLS_ERRORS, "VERIFY ERROR: depth=%d, subject=%s: %s",
	      cert_depth, subject, errstr);
	}
      else
	{
	  msg (D_TLS_ERRORS, "VERIFY ERROR: depth=%d, (could not extract X509 "
	      "subject string from certificate): %s", cert_depth, errstr);
	}

      /* Leave flags set to non-zero to indicate that the cert is not ok */
    }
  else if (SUCCESS != verify_cert(session, cert, cert_depth))
    {
      *flags |= MBEDTLS_X509_BADCERT_OTHER;
    }

  gc_free(&gc);

  /*
   * PolarSSL/mbed TLS-1.2.0+ expects 0 on anything except fatal errors.
   */
  return 0;
}

#ifdef ENABLE_X509ALTUSERNAME
# warning "X509 alt user name not yet supported for mbed TLS"
#endif

result_t
backend_x509_get_username (char *cn, int cn_len,
    char *x509_username_field, mbedtls_x509_crt *cert)
{
  mbedtls_x509_name *name;

  ASSERT( cn != NULL );

  name = &cert->subject;

  /* Find common name */
  while( name != NULL )
  {
      if (0 == memcmp (name->oid.p, MBEDTLS_OID_AT_CN,
	  MBEDTLS_OID_SIZE (MBEDTLS_OID_AT_CN)))
	break;

      name = name->next;
  }

  /* Not found, return an error if this is the peer's certificate */
  if( name == NULL )
      return FAILURE;

  /* Found, extract CN */
  if (cn_len > name->val.len)
    {
      memcpy( cn, name->val.p, name->val.len );
      cn[name->val.len] = '\0';
    }
  else
    {
      memcpy( cn, name->val.p, cn_len);
      cn[cn_len-1] = '\0';
    }

  return SUCCESS;
}

char *
backend_x509_get_serial (mbedtls_x509_crt *cert, struct gc_arena *gc)
{
  char *buf = NULL;
  size_t buflen = 0;
  mbedtls_mpi serial_mpi = { 0 };

  /* Transform asn1 integer serial into mbed TLS MPI */
  mbedtls_mpi_init(&serial_mpi);
  if (!mbed_ok(mbedtls_mpi_read_binary(&serial_mpi, cert->serial.p,
      cert->serial.len)))
    {
      msg(M_WARN, "Failed to retrieve serial from certificate.");
      goto end;
    }

  /* Determine decimal representation length, allocate buffer */
  mbedtls_mpi_write_string(&serial_mpi, 10, NULL, 0, &buflen);
  buf = gc_malloc(buflen, true, gc);

  /* Write MPI serial as decimal string into buffer */
  if (!mbed_ok(mbedtls_mpi_write_string(&serial_mpi, 10, buf, buflen, &buflen)))
    {
      msg(M_WARN, "Failed to write serial to string.");
      buf = NULL;
      goto end;
    }

end:
  mbedtls_mpi_free(&serial_mpi);
  return buf;
}

char *
backend_x509_get_serial_hex (mbedtls_x509_crt *cert, struct gc_arena *gc)
{
  char *buf = NULL;
  size_t len = cert->serial.len * 3 + 1;

  buf = gc_malloc(len, true, gc);

  if(mbedtls_x509_serial_gets(buf, len-1, &cert->serial) < 0)
    buf = NULL;

  return buf;
}

static struct buffer
x509_get_fingerprint (const mbedtls_md_info_t *md_info, mbedtls_x509_crt *cert,
    struct gc_arena *gc)
{
  const size_t md_size = mbedtls_md_get_size (md_info);
  struct buffer fingerprint = alloc_buf_gc (md_size, gc);
  mbedtls_md(md_info, cert->raw.p, cert->tbs.len, BPTR (&fingerprint));
  ASSERT (buf_inc_len(&fingerprint, md_size));
  return fingerprint;
}

struct buffer
x509_get_sha1_fingerprint (mbedtls_x509_crt *cert, struct gc_arena *gc)
{
  return x509_get_fingerprint(mbedtls_md_info_from_type(MBEDTLS_MD_SHA1),
      cert, gc);
}

struct buffer
x509_get_sha256_fingerprint (mbedtls_x509_crt *cert, struct gc_arena *gc)
{
  return x509_get_fingerprint(mbedtls_md_info_from_type(MBEDTLS_MD_SHA256),
      cert, gc);
}

char *
x509_get_subject(mbedtls_x509_crt *cert, struct gc_arena *gc)
{
  char tmp_subject[MAX_SUBJECT_LENGTH] = {0};
  char *subject = NULL;

  int ret = 0;

  ret = mbedtls_x509_dn_gets( tmp_subject, MAX_SUBJECT_LENGTH-1, &cert->subject );
  if (ret > 0)
    {
      /* Allocate the required space for the subject */
      subject = string_alloc(tmp_subject, gc);
    }

  return subject;
}

static void
do_setenv_x509 (struct env_set *es, const char *name, char *value, int depth)
{
  char *name_expand;
  size_t name_expand_size;

  string_mod (value, CC_ANY, CC_CRLF, '?');
  msg (D_X509_ATTR, "X509 ATTRIBUTE name='%s' value='%s' depth=%d", name, value, depth);
  name_expand_size = 64 + strlen (name);
  name_expand = (char *) malloc (name_expand_size);
  check_malloc_return (name_expand);
  openvpn_snprintf (name_expand, name_expand_size, "X509_%d_%s", depth, name);
  setenv_str (es, name_expand, value);
  free (name_expand);
}

static char *
asn1_buf_to_c_string(const mbedtls_asn1_buf *orig, struct gc_arena *gc)
{
  size_t i;
  char *val;

  for (i = 0; i < orig->len; ++i)
    if (orig->p[i] == '\0')
      return "ERROR: embedded null value";
  val = gc_malloc(orig->len+1, false, gc);
  memcpy(val, orig->p, orig->len);
  val[orig->len] = '\0';
  return val;
}

static void
do_setenv_name(struct env_set *es, const struct x509_track *xt,
	       const mbedtls_x509_crt *cert, int depth, struct gc_arena *gc)
{
  const mbedtls_x509_name *xn;
  for (xn = &cert->subject; xn != NULL; xn = xn->next)
    {
      const char *xn_short_name = NULL;
      if (0 == mbedtls_oid_get_attr_short_name (&xn->oid, &xn_short_name) &&
	  0 == strcmp (xt->name, xn_short_name))
	{
	  char *val_str = asn1_buf_to_c_string (&xn->val, gc);
	  do_setenv_x509 (es, xt->name, val_str, depth);
	}
    }
}

void
x509_track_add (const struct x509_track **ll_head, const char *name, int msglevel, struct gc_arena *gc)
{
  struct x509_track *xt;
  ALLOC_OBJ_CLEAR_GC (xt, struct x509_track, gc);
  if (*name == '+')
    {
      xt->flags |= XT_FULL_CHAIN;
      ++name;
    }
  xt->name = name;
  xt->next = *ll_head;
  *ll_head = xt;
}

void
x509_setenv_track (const struct x509_track *xt, struct env_set *es,
    const int depth, mbedtls_x509_crt *cert)
{
  struct gc_arena gc = gc_new();
  while (xt)
    {
      if (depth == 0 || (xt->flags & XT_FULL_CHAIN))
	{
	  if (0 == strcmp(xt->name, "SHA1") || 0 == strcmp(xt->name, "SHA256"))
	    {
	      /* Fingerprint is not part of X509 structure */
	      struct buffer cert_hash;
	      char *fingerprint;

	      if (0 == strcmp(xt->name, "SHA1"))
		cert_hash = x509_get_sha1_fingerprint(cert, &gc);
	      else
		cert_hash = x509_get_sha256_fingerprint(cert, &gc);

	      fingerprint = format_hex_ex(BPTR(&cert_hash),
		  BLEN(&cert_hash), 0, 1 | FHE_CAPS, ":", &gc);
	      do_setenv_x509(es, xt->name, fingerprint, depth);
	    }
	  else
	    {
	      do_setenv_name(es, xt, cert, depth, &gc);
	    }
	}
      xt = xt->next;
    }
  gc_free(&gc);
}

/*
 * Save X509 fields to environment, using the naming convention:
 *
 * X509_{cert_depth}_{name}={value}
 */
void
x509_setenv (struct env_set *es, int cert_depth, mbedtls_x509_crt *cert)
{
  int i;
  unsigned char c;
  const mbedtls_x509_name *name;
  char s[128] = { 0 };

  name = &cert->subject;

  while( name != NULL )
    {
      char name_expand[64+8];
      const char *shortname;

      if( 0 == mbedtls_oid_get_attr_short_name(&name->oid, &shortname) )
	{
	  openvpn_snprintf (name_expand, sizeof(name_expand), "X509_%d_%s",
	      cert_depth, shortname);
	}
      else
	{
	  openvpn_snprintf (name_expand, sizeof(name_expand), "X509_%d_\?\?",
	      cert_depth);
	}

      for( i = 0; i < name->val.len; i++ )
	{
	  if( i >= (int) sizeof( s ) - 1 )
	      break;

	  c = name->val.p[i];
	  if( c < 32 || c == 127 || ( c > 128 && c < 160 ) )
	       s[i] = '?';
	  else s[i] = c;
	}
	s[i] = '\0';

	/* Check both strings, set environment variable */
	string_mod (name_expand, CC_PRINT, CC_CRLF, '_');
	string_mod ((char*)s, CC_PRINT, CC_CRLF, '_');
	setenv_str_incr (es, name_expand, (char*)s);

	name = name->next;
    }
}

result_t
x509_verify_ns_cert_type(const mbedtls_x509_crt *cert, const int usage)
{
  if (usage == NS_CERT_CHECK_NONE)
    return SUCCESS;
  if (usage == NS_CERT_CHECK_CLIENT)
    return ((cert->ext_types & MBEDTLS_X509_EXT_NS_CERT_TYPE)
	&& (cert->ns_cert_type & MBEDTLS_X509_NS_CERT_TYPE_SSL_CLIENT)) ?
	    SUCCESS : FAILURE;
  if (usage == NS_CERT_CHECK_SERVER)
    return ((cert->ext_types & MBEDTLS_X509_EXT_NS_CERT_TYPE)
	&& (cert->ns_cert_type & MBEDTLS_X509_NS_CERT_TYPE_SSL_SERVER)) ?
	    SUCCESS : FAILURE;

  return FAILURE;
}

result_t
x509_verify_cert_ku (mbedtls_x509_crt *cert, const unsigned * const expected_ku,
    int expected_len)
{
  result_t fFound = FAILURE;

  if(!(cert->ext_types & MBEDTLS_X509_EXT_KEY_USAGE))
    {
      msg (D_HANDSHAKE, "Certificate does not have key usage extension");
    }
  else
    {
      int i;
      unsigned nku = cert->key_usage;

      msg (D_HANDSHAKE, "Validating certificate key usage");
      for (i=0; SUCCESS != fFound && i<expected_len; i++)
	{
	  if (expected_ku[i] != 0)
	    {
	      msg (D_HANDSHAKE, "++ Certificate has key usage  %04x, expects "
		  "%04x", nku, expected_ku[i]);

	      if (nku == expected_ku[i])
		{
		  fFound = SUCCESS;
		}
	    }
	}
    }
  return fFound;
}

result_t
x509_verify_cert_eku (mbedtls_x509_crt *cert, const char * const expected_oid)
{
  result_t fFound = FAILURE;

  if (!(cert->ext_types & MBEDTLS_X509_EXT_EXTENDED_KEY_USAGE))
    {
      msg (D_HANDSHAKE, "Certificate does not have extended key usage extension");
    }
  else
    {
      mbedtls_x509_sequence *oid_seq = &(cert->ext_key_usage);

      msg (D_HANDSHAKE, "Validating certificate extended key usage");
      while (oid_seq != NULL)
	{
	  mbedtls_x509_buf *oid = &oid_seq->buf;
	  char oid_num_str[1024];
	  const char *oid_str;

	  if (0 == mbedtls_oid_get_extended_key_usage( oid, &oid_str ))
	    {
	      msg (D_HANDSHAKE, "++ Certificate has EKU (str) %s, expects %s",
		  oid_str, expected_oid);
	      if (!strcmp (expected_oid, oid_str))
		{
		  fFound = SUCCESS;
		  break;
		}
	    }

	  if (0 < mbedtls_oid_get_numeric_string( oid_num_str,
	      sizeof (oid_num_str), oid))
	    {
	      msg (D_HANDSHAKE, "++ Certificate has EKU (oid) %s, expects %s",
		  oid_num_str, expected_oid);
	      if (!strcmp (expected_oid, oid_num_str))
		{
		  fFound = SUCCESS;
		  break;
		}
	    }
	  oid_seq = oid_seq->next;
	}
    }

    return fFound;
}

result_t
x509_write_pem(FILE *peercert_file, mbedtls_x509_crt *peercert)
{
    msg (M_WARN, "mbed TLS does not support writing peer certificate in PEM format");
    return FAILURE;
}

bool
tls_verify_crl_missing(const struct tls_options *opt)
{
  if (opt->crl_file && !(opt->ssl_flags & SSLF_CRL_VERIFY_DIR)
      && (opt->ssl_ctx.crl == NULL || opt->ssl_ctx.crl->version == 0))
    {
      return true;
    }
  return false;
}

#endif /* #if defined(ENABLE_CRYPTO) && defined(ENABLE_CRYPTO_MBEDTLS) */