2 * Verify established TLS connections.
4 * Copyright (C) 2011 Simon Ruderich
6 * This program is free software: you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation, either version 3 of the License, or
9 * (at your option) any later version.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program. If not, see <http://www.gnu.org/licenses/>.
26 #include <gnutls/x509.h>
29 int verify_tls_connection(gnutls_session_t session, const char *hostname) {
35 gnutls_x509_crt_t cert;
36 const gnutls_datum_t *cert_list;
37 unsigned int cert_list_size;
39 char buffer[66]; /* one line in a PEM file is 64 bytes + '\n' + '\0' */
40 char server_cert[8192];
41 char stored_cert[8192];
43 result = gnutls_certificate_verify_peers2(session, &status);
44 /* Verification failed (!= invalid certificate but worse), no need for any
48 "verify_tls_connection(): gnutls_certificate_verify_peers2() failed: %s",
49 gnutls_strerror(result));
52 /* Definitely an invalid certificate, abort. */
53 if (status & GNUTLS_CERT_EXPIRED
54 || status & GNUTLS_CERT_REVOKED
55 || status & GNUTLS_CERT_NOT_ACTIVATED
56 || status & GNUTLS_CERT_INSECURE_ALGORITHM) {
58 "verify_tls_connection(): invalid server certificate");
62 /* We only handle X509 certificates for now. Let validation fail to
63 * prevent an attacker from changing the certificate type to prevent
65 if (GNUTLS_CRT_X509 != gnutls_certificate_type_get(session)) {
67 "verify_tls_connection(): no X509 server certificate");
71 /* Get server certificate. */
73 if (0 > (result = gnutls_x509_crt_init(&cert))) {
75 "verify_tls_connection(): gnutls_x509_crt_init() failed: %s",
76 gnutls_strerror(result));
80 cert_list = gnutls_certificate_get_peers(session, &cert_list_size);
81 if (NULL == cert_list) {
83 "verify_tls_connection(): gnutls_certificate_get_peers() failed");
84 gnutls_x509_crt_deinit(cert);
88 if (0 > (result = gnutls_x509_crt_import(cert, &cert_list[0],
89 GNUTLS_X509_FMT_DER))) {
91 "verify_tls_connection(): gnutls_x509_crt_import() failed: %s",
92 gnutls_strerror(result));
93 gnutls_x509_crt_deinit(cert);
97 /* Export the certificate as PEM to compare it with the known certificate
99 size = sizeof(server_cert);
100 result = gnutls_x509_crt_export(cert, GNUTLS_X509_FMT_PEM,
102 if (GNUTLS_E_SUCCESS != result) {
104 "verify_tls_connection(): gnutls_x509_crt_export() failed: %s",
105 gnutls_strerror(result));
106 gnutls_x509_crt_deinit(cert);
109 /* We got the certificate as PEM, free the crt struct. */
110 gnutls_x509_crt_deinit(cert);
112 /* Open stored server certificate file. */
113 if (0 != server_certificate_path(&file, hostname, path, sizeof(path))) {
118 stored_cert[0] = '\0'; /* for strcat() */
120 while (NULL != fgets(buffer, sizeof(buffer), file)) {
121 size += strlen(buffer);
122 /* Make sure the buffer is big enough. */
123 if (sizeof(stored_cert) <= size) {
124 LOG(LOG_WARNING, "verify_tls_connection(): '%s' too big",
130 strcat(stored_cert, buffer);
135 "verify_tls_connection(): failed to read from '%s': %s",
136 path, strerror(errno));
141 /* Check if the server certificate matches our stored certificate. */
142 if (0 != strcmp(stored_cert, server_cert)) {
144 "verify_tls_connection(): server certificate changed!",
145 path, strerror(errno));
152 int server_certificate_path(FILE **file, const char *hostname, char *path, size_t size) {
153 /* Hostname too long. */
154 if (size - strlen(STORED_SERVER_CERT_FORMAT) <= strlen(hostname)) {
156 "server_certificate_path(): hostname too long: '%s'",
160 /* Try to prevent path traversals in hostnames. */
161 if (NULL != strstr(hostname, "..")) {
163 "server_certificate_path(): possible path traversal: '%s'",
167 snprintf(path, size, STORED_SERVER_CERT_FORMAT, hostname);
169 /* Open the stored certificate file. */
170 *file = fopen(path, "rb");
172 LOG(global_passthrough_unknown ? LOG_DEBUG : LOG_WARNING,
173 "server_certificate_path(): failed to open '%s': %s",
174 path, strerror(errno));
175 /* Couldn't open the file, special case. */