summary refs log tree commit diff
path: root/tls_verify.c
blob: acbe163ffdf8ce77626ba8f3e9e1b876ebe9875f (plain) (blame)
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
/* $OpenBSD: tls_verify.c,v 1.20 2018/02/05 00:52:24 jsing Exp $ */
/*
 * Copyright (c) 2014 Jeremie Courreges-Anglas <jca@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/socket.h>

#include <arpa/inet.h>
#include <netinet/in.h>

#include <string.h>

#include <openssl/x509v3.h>

#include <tls.h>
#include "tls_internal.h"

static int
tls_match_name(const char *cert_name, const char *name)
{
	const char *cert_domain, *domain, *next_dot;

	if (strcasecmp(cert_name, name) == 0)
		return 0;

	/* Wildcard match? */
	if (cert_name[0] == '*') {
		/*
		 * Valid wildcards:
		 * - "*.domain.tld"
		 * - "*.sub.domain.tld"
		 * - etc.
		 * Reject "*.tld".
		 * No attempt to prevent the use of eg. "*.co.uk".
		 */
		cert_domain = &cert_name[1];
		/* Disallow "*"  */
		if (cert_domain[0] == '\0')
			return -1;
		/* Disallow "*foo" */
		if (cert_domain[0] != '.')
			return -1;
		/* Disallow "*.." */
		if (cert_domain[1] == '.')
			return -1;
		next_dot = strchr(&cert_domain[1], '.');
		/* Disallow "*.bar" */
		if (next_dot == NULL)
			return -1;
		/* Disallow "*.bar.." */
		if (next_dot[1] == '.')
			return -1;

		domain = strchr(name, '.');

		/* No wildcard match against a name with no host part. */
		if (name[0] == '.')
			return -1;
		/* No wildcard match against a name with no domain part. */
		if (domain == NULL || strlen(domain) == 1)
			return -1;

		if (strcasecmp(cert_domain, domain) == 0)
			return 0;
	}

	return -1;
}

/*
 * See RFC 5280 section 4.2.1.6 for SubjectAltName details.
 * alt_match is set to 1 if a matching alternate name is found.
 * alt_exists is set to 1 if any known alternate name exists in the certificate.
 */
static int
tls_check_subject_altname(struct tls *ctx, X509 *cert, const char *name,
    int *alt_match, int *alt_exists)
{
	STACK_OF(GENERAL_NAME) *altname_stack = NULL;
	union tls_addr addrbuf;
	int addrlen, type;
	int count, i;
	int rv = 0;

	*alt_match = 0;
	*alt_exists = 0;

	altname_stack = X509_get_ext_d2i(cert, NID_subject_alt_name,
	    NULL, NULL);
	if (altname_stack == NULL)
		return 0;

	if (inet_pton(AF_INET, name, &addrbuf) == 1) {
		type = GEN_IPADD;
		addrlen = 4;
	} else if (inet_pton(AF_INET6, name, &addrbuf) == 1) {
		type = GEN_IPADD;
		addrlen = 16;
	} else {
		type = GEN_DNS;
		addrlen = 0;
	}

	count = sk_GENERAL_NAME_num(altname_stack);
	for (i = 0; i < count; i++) {
		GENERAL_NAME	*altname;

		altname = sk_GENERAL_NAME_value(altname_stack, i);

		if (altname->type == GEN_DNS || altname->type == GEN_IPADD)
			*alt_exists = 1;

		if (altname->type != type)
			continue;

		if (type == GEN_DNS) {
			unsigned char	*data;
			int		 format, len;

			format = ASN1_STRING_type(altname->d.dNSName);
			if (format == V_ASN1_IA5STRING) {
				data = ASN1_STRING_data(altname->d.dNSName);
				len = ASN1_STRING_length(altname->d.dNSName);

				if (len < 0 || (size_t)len != strlen(data)) {
					tls_set_errorx(ctx,
					    "error verifying name '%s': "
					    "NUL byte in subjectAltName, "
					    "probably a malicious certificate",
					    name);
					rv = -1;
					break;
				}

				/*
				 * Per RFC 5280 section 4.2.1.6:
				 * " " is a legal domain name, but that
				 * dNSName must be rejected.
				 */
				if (strcmp(data, " ") == 0) {
					tls_set_errorx(ctx,
					    "error verifying name '%s': "
					    "a dNSName of \" \" must not be "
					    "used", name);
					rv = -1;
					break;
				}

				if (tls_match_name(data, name) == 0) {
					*alt_match = 1;
					break;
				}
			} else {
#ifdef DEBUG
				fprintf(stdout, "%s: unhandled subjectAltName "
				    "dNSName encoding (%d)\n", getprogname(),
				    format);
#endif
			}

		} else if (type == GEN_IPADD) {
			unsigned char	*data;
			int		 datalen;

			datalen = ASN1_STRING_length(altname->d.iPAddress);
			data = ASN1_STRING_data(altname->d.iPAddress);

			if (datalen < 0) {
				tls_set_errorx(ctx,
				    "Unexpected negative length for an "
				    "IP address: %d", datalen);
				rv = -1;
				break;
			}

			/*
			 * Per RFC 5280 section 4.2.1.6:
			 * IPv4 must use 4 octets and IPv6 must use 16 octets.
			 */
			if (datalen == addrlen &&
			    memcmp(data, &addrbuf, addrlen) == 0) {
				*alt_match = 1;
				break;
			}
		}
	}

	sk_GENERAL_NAME_pop_free(altname_stack, GENERAL_NAME_free);
	return rv;
}

static int
tls_check_common_name(struct tls *ctx, X509 *cert, const char *name,
    int *cn_match)
{
	X509_NAME *subject_name;
	char *common_name = NULL;
	union tls_addr addrbuf;
	int common_name_len;
	int rv = 0;

	*cn_match = 0;

	subject_name = X509_get_subject_name(cert);
	if (subject_name == NULL)
		goto done;

	common_name_len = X509_NAME_get_text_by_NID(subject_name,
	    NID_commonName, NULL, 0);
	if (common_name_len < 0)
		goto done;

	common_name = calloc(common_name_len + 1, 1);
	if (common_name == NULL)
		goto done;

	X509_NAME_get_text_by_NID(subject_name, NID_commonName, common_name,
	    common_name_len + 1);

	/* NUL bytes in CN? */
	if (common_name_len < 0 ||
	    (size_t)common_name_len != strlen(common_name)) {
		tls_set_errorx(ctx, "error verifying name '%s': "
		    "NUL byte in Common Name field, "
		    "probably a malicious certificate", name);
		rv = -1;
		goto done;
	}

	/*
	 * We don't want to attempt wildcard matching against IP addresses,
	 * so perform a simple comparison here.
	 */
	if (inet_pton(AF_INET,  name, &addrbuf) == 1 ||
	    inet_pton(AF_INET6, name, &addrbuf) == 1) {
		if (strcmp(common_name, name) == 0)
			*cn_match = 1;
		goto done;
	}

	if (tls_match_name(common_name, name) == 0)
		*cn_match = 1;

 done:
	free(common_name);
	return rv;
}

int
tls_check_name(struct tls *ctx, X509 *cert, const char *name, int *match)
{
	int alt_exists;

	*match = 0;

	if (tls_check_subject_altname(ctx, cert, name, match,
	    &alt_exists) == -1)
		return -1;

	/*
	 * As per RFC 6125 section 6.4.4, if any known alternate name existed
	 * in the certificate, we do not attempt to match on the CN.
	 */
	if (*match || alt_exists)
		return 0;

	return tls_check_common_name(ctx, cert, name, match);
}