summaryrefslogtreecommitdiffstats
path: root/src/tls/tls_verify.c
blob: 85d5f649d4d2fb5f7cccbd6c1b97788327f2a388 (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
/*++
/* NAME
/*	tls_verify 3
/* SUMMARY
/*	peer name and peer certificate verification
/* SYNOPSIS
/*	#define TLS_INTERNAL
/*	#include <tls.h>
/*
/*	int	tls_verify_certificate_callback(ok, ctx)
/*	int	ok;
/*	X509_STORE_CTX *ctx;
/*
/*	int     tls_log_verify_error(TLScontext)
/*	TLS_SESS_STATE *TLScontext;
/*
/*	char *tls_peer_CN(peercert, TLScontext)
/*	X509   *peercert;
/*	TLS_SESS_STATE *TLScontext;
/*
/*	char *tls_issuer_CN(peercert, TLScontext)
/*	X509   *peercert;
/*	TLS_SESS_STATE *TLScontext;
/*
/*	const char *tls_dns_name(gn, TLScontext)
/*	const GENERAL_NAME *gn;
/*	TLS_SESS_STATE *TLScontext;
/* DESCRIPTION
/*	tls_verify_certificate_callback() is called several times (directly
/*	or indirectly) from crypto/x509/x509_vfy.c. It collects errors
/*	and trust information at each element of the trust chain.
/*	The last call at depth 0 sets the verification status based
/*	on the cumulative winner (lowest depth) of errors vs. trust.
/*	We always return 1 (continue the handshake) and handle trust
/*	and peer-name verification problems at the application level.
/*
/*	tls_log_verify_error() (called only when we care about the
/*	peer certificate, that is not when opportunistic) logs the
/*	reason why the certificate failed to be verified.
/*
/*	tls_peer_CN() returns the text CommonName for the peer
/*	certificate subject, or an empty string if no CommonName was
/*	found. The result is allocated with mymalloc() and must be
/*	freed by the caller; it contains UTF-8 without non-printable
/*	ASCII characters.
/*
/*	tls_issuer_CN() returns the text CommonName for the peer
/*	certificate issuer, or an empty string if no CommonName was
/*	found. The result is allocated with mymalloc() and must be
/*	freed by the caller; it contains UTF-8 without non-printable
/*	ASCII characters.
/*
/*	tls_dns_name() returns the string value of a GENERAL_NAME
/*	from a DNS subjectAltName extension. If non-printable characters
/*	are found, a null string is returned instead. Further sanity
/*	checks may be added if the need arises.
/*
/*	Arguments:
/* .IP ok
/*	Result of prior verification: non-zero means success.  In
/*	order to reduce the noise level, some tests or error reports
/*	are disabled when verification failed because of some
/*	earlier problem.
/* .IP ctx
/*	SSL application context. This links to the Postfix TLScontext
/*	with enforcement and logging options.
/* .IP gn
/*	An OpenSSL GENERAL_NAME structure holding a DNS subjectAltName
/*	to be decoded and checked for validity.
/* .IP peercert
/*	Server or client X.509 certificate.
/* .IP TLScontext
/*	Server or client context for warning messages.
/* DIAGNOSTICS
/*	tls_peer_CN(), tls_issuer_CN() and tls_dns_name() log a warning
/*	when 1) the requested information is not available in the specified
/*	certificate, 2) the result exceeds a fixed limit, 3) the result
/*	contains NUL characters or the result contains non-printable or
/*	non-ASCII characters.
/* LICENSE
/* .ad
/* .fi
/*	This software is free. You can do with it whatever you want.
/*	The original author kindly requests that you acknowledge
/*	the use of his software.
/* AUTHOR(S)
/*	Originally written by:
/*	Lutz Jaenicke
/*	BTU Cottbus
/*	Allgemeine Elektrotechnik
/*	Universitaetsplatz 3-4
/*	D-03044 Cottbus, Germany
/*
/*	Updated by:
/*	Wietse Venema
/*	IBM T.J. Watson Research
/*	P.O. Box 704
/*	Yorktown Heights, NY 10598, USA
/*
/*	Victor Duchovni
/*	Morgan Stanley
/*--*/

/* System library. */

#include <sys_defs.h>
#include <ctype.h>

#ifdef USE_TLS
#include <string.h>

/* Utility library. */

#include <msg.h>
#include <mymalloc.h>
#include <stringops.h>

/* TLS library. */

#define TLS_INTERNAL
#include <tls.h>

/* update_error_state - safely stash away error state */

static void update_error_state(TLS_SESS_STATE *TLScontext, int depth,
			               X509 *errorcert, int errorcode)
{
    /* No news is good news */
    if (TLScontext->errordepth >= 0 && TLScontext->errordepth <= depth)
	return;

    /*
     * The certificate pointer is stable during the verification callback,
     * but may be freed after the callback returns.  Since we delay error
     * reporting till later, we bump the refcount so we can rely on it still
     * being there until later.
     */
    if (TLScontext->errorcert != 0)
	X509_free(TLScontext->errorcert);
    if (errorcert != 0)
	X509_up_ref(errorcert);
    TLScontext->errorcert = errorcert;
    TLScontext->errorcode = errorcode;
    TLScontext->errordepth = depth;
}

/* tls_verify_certificate_callback - verify peer certificate info */

int     tls_verify_certificate_callback(int ok, X509_STORE_CTX *ctx)
{
    char    buf[CCERT_BUFSIZ];
    X509   *cert;
    int     err;
    int     depth;
    int     max_depth;
    SSL    *con;
    TLS_SESS_STATE *TLScontext;

    /* May be NULL as of OpenSSL 1.0, thanks for the API change! */
    cert = X509_STORE_CTX_get_current_cert(ctx);
    err = X509_STORE_CTX_get_error(ctx);
    con = X509_STORE_CTX_get_ex_data(ctx, SSL_get_ex_data_X509_STORE_CTX_idx());
    TLScontext = SSL_get_ex_data(con, TLScontext_index);
    depth = X509_STORE_CTX_get_error_depth(ctx);

    /* Don't log the internal root CA unless there's an unexpected error. */
    if (ok && TLScontext->tadepth > 0 && depth > TLScontext->tadepth)
	return (1);

    /*
     * Certificate chain depth limit violations are mis-reported by the
     * OpenSSL library, from SSL_CTX_set_verify(3):
     * 
     * The certificate verification depth set with SSL[_CTX]_verify_depth()
     * stops the verification at a certain depth. The error message produced
     * will be that of an incomplete certificate chain and not
     * X509_V_ERR_CERT_CHAIN_TOO_LONG as may be expected.
     * 
     * We set a limit that is one higher than the user requested limit. If this
     * higher limit is reached, we raise an error even a trusted root CA is
     * present at this depth. This disambiguates trust chain truncation from
     * an incomplete trust chain.
     */
    max_depth = SSL_get_verify_depth(con) - 1;

    /*
     * We never terminate the SSL handshake in the verification callback,
     * rather we allow the TLS handshake to continue, but mark the session as
     * unverified. The application is responsible for closing any sessions
     * with unverified credentials.
     */
    if (max_depth >= 0 && depth > max_depth) {
	X509_STORE_CTX_set_error(ctx, err = X509_V_ERR_CERT_CHAIN_TOO_LONG);
	ok = 0;
    }
    if (ok == 0)
	update_error_state(TLScontext, depth, cert, err);

    if (TLScontext->log_mask & TLS_LOG_VERBOSE) {
	if (cert)
	    X509_NAME_oneline(X509_get_subject_name(cert), buf, sizeof(buf));
	else
	    strcpy(buf, "<unknown>");
	msg_info("%s: depth=%d verify=%d subject=%s",
		 TLScontext->namaddr, depth, ok, printable(buf, '?'));
    }
    return (1);
}

/* tls_log_verify_error - Report final verification error status */

void    tls_log_verify_error(TLS_SESS_STATE *TLScontext)
{
    char    buf[CCERT_BUFSIZ];
    int     err = TLScontext->errorcode;
    X509   *cert = TLScontext->errorcert;
    int     depth = TLScontext->errordepth;

#define PURPOSE ((depth>0) ? "CA": TLScontext->am_server ? "client": "server")

    if (err == X509_V_OK)
	return;

    /*
     * Specific causes for verification failure.
     */
    switch (err) {
    case X509_V_ERR_CERT_UNTRUSTED:

	/*
	 * We expect the error cert to be the leaf, but it is likely
	 * sufficient to omit it from the log, even less user confusion.
	 */
	msg_info("certificate verification failed for %s: "
		 "not trusted by local or TLSA policy", TLScontext->namaddr);
	break;
    case X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT:
	msg_info("certificate verification failed for %s: "
		 "self-signed certificate", TLScontext->namaddr);
	break;
    case X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY:
    case X509_V_ERR_SELF_SIGNED_CERT_IN_CHAIN:

	/*
	 * There is no difference between issuing cert not provided and
	 * provided, but not found in CAfile/CApath. Either way, we don't
	 * trust it.
	 */
	if (cert)
	    X509_NAME_oneline(X509_get_issuer_name(cert), buf, sizeof(buf));
	else
	    strcpy(buf, "<unknown>");
	msg_info("certificate verification failed for %s: untrusted issuer %s",
		 TLScontext->namaddr, printable(buf, '?'));
	break;
    case X509_V_ERR_CERT_NOT_YET_VALID:
    case X509_V_ERR_ERROR_IN_CERT_NOT_BEFORE_FIELD:
	msg_info("%s certificate verification failed for %s: certificate not"
		 " yet valid", PURPOSE, TLScontext->namaddr);
	break;
    case X509_V_ERR_CERT_HAS_EXPIRED:
    case X509_V_ERR_ERROR_IN_CERT_NOT_AFTER_FIELD:
	msg_info("%s certificate verification failed for %s: certificate has"
		 " expired", PURPOSE, TLScontext->namaddr);
	break;
    case X509_V_ERR_INVALID_PURPOSE:
	msg_info("certificate verification failed for %s: not designated for "
		 "use as a %s certificate", TLScontext->namaddr, PURPOSE);
	break;
    case X509_V_ERR_CERT_CHAIN_TOO_LONG:
	msg_info("certificate verification failed for %s: "
		 "certificate chain longer than limit(%d)",
		 TLScontext->namaddr, depth - 1);
	break;
    default:
	msg_info("%s certificate verification failed for %s: num=%d:%s",
		 PURPOSE, TLScontext->namaddr, err,
		 X509_verify_cert_error_string(err));
	break;
    }
}

#ifndef DONT_GRIPE
#define DONT_GRIPE 0
#define DO_GRIPE 1
#endif

/* tls_text_name - extract certificate property value by name */

static char *tls_text_name(X509_NAME *name, int nid, const char *label,
			        const TLS_SESS_STATE *TLScontext, int gripe)
{
    const char *myname = "tls_text_name";
    int     pos;
    X509_NAME_ENTRY *entry;
    ASN1_STRING *entry_str;
    int     asn1_type;
    int     utf8_length;
    unsigned char *utf8_value;
    int     ch;
    unsigned char *cp;

    if (name == 0 || (pos = X509_NAME_get_index_by_NID(name, nid, -1)) < 0) {
	if (gripe != DONT_GRIPE) {
	    msg_warn("%s: %s: peer certificate has no %s",
		     myname, TLScontext->namaddr, label);
	    tls_print_errors();
	}
	return (0);
    }
#if 0

    /*
     * If the match is required unambiguous, insist that that no other values
     * be present.
     */
    if (X509_NAME_get_index_by_NID(name, nid, pos) >= 0) {
	msg_warn("%s: %s: multiple %ss in peer certificate",
		 myname, TLScontext->namaddr, label);
	return (0);
    }
#endif

    if ((entry = X509_NAME_get_entry(name, pos)) == 0) {
	/* This should not happen */
	msg_warn("%s: %s: error reading peer certificate %s entry",
		 myname, TLScontext->namaddr, label);
	tls_print_errors();
	return (0);
    }
    if ((entry_str = X509_NAME_ENTRY_get_data(entry)) == 0) {
	/* This should not happen */
	msg_warn("%s: %s: error reading peer certificate %s data",
		 myname, TLScontext->namaddr, label);
	tls_print_errors();
	return (0);
    }

    /*
     * XXX Convert everything into UTF-8. This is a super-set of ASCII, so we
     * don't have to bother with separate code paths for ASCII-like content.
     * If the payload is ASCII then we won't waste lots of CPU cycles
     * converting it into UTF-8. It's up to OpenSSL to do something
     * reasonable when converting ASCII formats that contain non-ASCII
     * content.
     * 
     * XXX Don't bother optimizing the string length error check. It is not
     * worth the complexity.
     */
    asn1_type = ASN1_STRING_type(entry_str);
    if ((utf8_length = ASN1_STRING_to_UTF8(&utf8_value, entry_str)) < 0) {
	msg_warn("%s: %s: error decoding peer %s of ASN.1 type=%d",
		 myname, TLScontext->namaddr, label, asn1_type);
	tls_print_errors();
	return (0);
    }

    /*
     * No returns without cleaning up. A good optimizer will replace multiple
     * blocks of identical code by jumps to just one such block.
     */
#define TLS_TEXT_NAME_RETURN(x) do { \
	char *__tls_text_name_temp = (x); \
	OPENSSL_free(utf8_value); \
	return (__tls_text_name_temp); \
    } while (0)

    /*
     * Remove trailing null characters. They would give false alarms with the
     * length check and with the embedded null check.
     */
#define TRIM0(s, l) do { while ((l) > 0 && (s)[(l)-1] == 0) --(l); } while (0)

    TRIM0(utf8_value, utf8_length);

    /*
     * Enforce the length limit, because the caller will copy the result into
     * a fixed-length buffer.
     */
    if (utf8_length >= CCERT_BUFSIZ) {
	msg_warn("%s: %s: peer %s too long: %d",
		 myname, TLScontext->namaddr, label, utf8_length);
	TLS_TEXT_NAME_RETURN(0);
    }

    /*
     * Reject embedded nulls in ASCII or UTF-8 names. OpenSSL is responsible
     * for producing properly-formatted UTF-8.
     */
    if (utf8_length != strlen((char *) utf8_value)) {
	msg_warn("%s: %s: NULL character in peer %s",
		 myname, TLScontext->namaddr, label);
	TLS_TEXT_NAME_RETURN(0);
    }

    /*
     * Reject non-printable ASCII characters in UTF-8 content.
     * 
     * Note: the code below does not find control characters in illegal UTF-8
     * sequences. It's OpenSSL's job to produce valid UTF-8, and reportedly,
     * it does validation.
     */
    for (cp = utf8_value; (ch = *cp) != 0; cp++) {
	if (ISASCII(ch) && !ISPRINT(ch)) {
	    msg_warn("%s: %s: non-printable content in peer %s",
		     myname, TLScontext->namaddr, label);
	    TLS_TEXT_NAME_RETURN(0);
	}
    }
    TLS_TEXT_NAME_RETURN(mystrdup((char *) utf8_value));
}

/* tls_dns_name - Extract valid DNS name from subjectAltName value */

const char *tls_dns_name(const GENERAL_NAME * gn,
			         const TLS_SESS_STATE *TLScontext)
{
    const char *myname = "tls_dns_name";
    char   *cp;
    const char *dnsname;
    int     len;

    /*
     * Peername checks are security sensitive, carefully scrutinize the
     * input!
     */
    if (gn->type != GEN_DNS)
	msg_panic("%s: Non DNS input argument", myname);

    /*
     * We expect the OpenSSL library to construct GEN_DNS extension objects as
     * ASN1_IA5STRING values. Check we got the right union member.
     */
    if (ASN1_STRING_type(gn->d.ia5) != V_ASN1_IA5STRING) {
	msg_warn("%s: %s: invalid ASN1 value type in subjectAltName",
		 myname, TLScontext->namaddr);
	return (0);
    }

    /*
     * Safe to treat as an ASCII string possibly holding a DNS name
     */
    dnsname = (const char *) ASN1_STRING_get0_data(gn->d.ia5);
    len = ASN1_STRING_length(gn->d.ia5);
    TRIM0(dnsname, len);

    /*
     * Per Dr. Steven Henson of the OpenSSL development team, ASN1_IA5STRING
     * values can have internal ASCII NUL values in this context because
     * their length is taken from the decoded ASN1 buffer, a trailing NUL is
     * always appended to make sure that the string is terminated, but the
     * ASN.1 length may differ from strlen().
     */
    if (len != strlen(dnsname)) {
	msg_warn("%s: %s: internal NUL in subjectAltName",
		 myname, TLScontext->namaddr);
	return 0;
    }

    /*
     * XXX: Should we be more strict and call valid_hostname()? So long as
     * the name is safe to handle, if it is not a valid hostname, it will not
     * compare equal to the expected peername, so being more strict than
     * "printable" is likely excessive...
     */
    if (*dnsname && !allprint(dnsname)) {
	cp = mystrdup(dnsname);
	msg_warn("%s: %s: non-printable characters in subjectAltName: %.100s",
		 myname, TLScontext->namaddr, printable(cp, '?'));
	myfree(cp);
	return 0;
    }
    return (dnsname);
}

/* tls_peer_CN - extract peer common name from certificate */

char   *tls_peer_CN(X509 *peercert, const TLS_SESS_STATE *TLScontext)
{
    char   *cn;

    cn = tls_text_name(X509_get_subject_name(peercert), NID_commonName,
		       "subject CN", TLScontext, DONT_GRIPE);
    return (cn ? cn : mystrdup(""));
}

/* tls_issuer_CN - extract issuer common name from certificate */

char   *tls_issuer_CN(X509 *peer, const TLS_SESS_STATE *TLScontext)
{
    X509_NAME *name;
    char   *cn;

    name = X509_get_issuer_name(peer);

    /*
     * If no issuer CN field, use Organization instead. CA certs without a CN
     * are common, so we only complain if the organization is also missing.
     */
    if ((cn = tls_text_name(name, NID_commonName,
			    "issuer CN", TLScontext, DONT_GRIPE)) == 0)
	cn = tls_text_name(name, NID_organizationName,
			   "issuer Organization", TLScontext, DONT_GRIPE);
    return (cn ? cn : mystrdup(""));
}

#endif