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diff --git a/src/Makefile.am b/src/Makefile.am
index 728b4f8..4f92b03 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -14,6 +14,7 @@ axel_SOURCES = \
search.c \
search.h \
ssl.c \
+ ssl_verify.c \
ssl.h \
tcp.c \
tcp.h \
diff --git a/src/ssl.c b/src/ssl.c
index 6c7ae75..fc1ef05 100644
--- a/src/ssl.c
+++ b/src/ssl.c
@@ -71,7 +71,7 @@ ssl_startup(void)
SSL *
ssl_connect(int fd, char *hostname, char *message)
{
-
+ X509 *server_cert;
SSL_CTX *ssl_ctx;
SSL *ssl;
@@ -92,9 +92,33 @@ ssl_connect(int fd, char *hostname, char *message)
if (err <= 0) {
sprintf(message, _("SSL error: %s\n"),
ERR_reason_error_string(ERR_get_error()));
+ SSL_CTX_free(ssl_ctx);
+ return NULL;
+ }
+
+ err = SSL_get_verify_result(ssl);
+ if (err != X509_V_OK) {
+ fprintf(stderr, _("SSL error: Certificate error"));
+ SSL_CTX_free(ssl_ctx);
return NULL;
}
+ server_cert = SSL_get_peer_certificate(ssl);
+ if (server_cert == NULL) {
+ fprintf(stderr, _("SSL error: Certificate not found"));
+ SSL_CTX_free(ssl_ctx);
+ return NULL;
+ }
+
+ if (!ssl_validate_hostname(hostname, server_cert)) {
+ fprintf(stderr, _("SSL error: Hostname verification failed"));
+ X509_free(server_cert);
+ SSL_CTX_free(ssl_ctx);
+ return NULL;
+ }
+
+ X509_free(server_cert);
+
return ssl;
}
diff --git a/src/ssl.h b/src/ssl.h
index cc00eaf..64fb933 100644
--- a/src/ssl.h
+++ b/src/ssl.h
@@ -44,5 +44,6 @@
void ssl_init(conf_t *conf);
SSL *ssl_connect(int fd, char *hostname, char *message);
void ssl_disconnect(SSL *ssl);
+bool ssl_validate_hostname(const char *hostname, const X509 *server_cert);
#endif /* AXEL_SSL_H */
diff --git a/src/ssl_verify.c b/src/ssl_verify.c
new file mode 100644
index 0000000..8a67a3c
--- /dev/null
+++ b/src/ssl_verify.c
@@ -0,0 +1,147 @@
+/*
+ Helper functions to perform basic hostname validation using OpenSSL.
+
+ Author: Alban Diquet
+ Copyright (C) 2012, iSEC Partners.
+
+ Permission is hereby granted, free of charge, to any person obtaining a copy of
+ this software and associated documentation files (the "Software"), to deal in
+ the Software without restriction, including without limitation the rights to
+ use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+ of the Software, and to permit persons to whom the Software is furnished to do
+ so, subject to the following conditions:
+
+ The above copyright notice and this permission notice shall be included in all
+ copies or substantial portions of the Software.
+
+ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ SOFTWARE.
+ */
+
+#include "axel.h"
+
+#ifdef HAVE_SSL
+
+#include <openssl/ssl.h>
+#include <openssl/x509v3.h>
+
+#if OPENSSL_VERSION_NUMBER < 0x10101000L
+#define ASN1_STRING_data_compat ASN1_STRING_data
+#else
+#define ASN1_STRING_data_compat ASN1_STRING_get0_data
+#endif
+
+typedef enum {
+ MatchFound,
+ MatchNotFound,
+ NoSANPresent,
+ MalformedCertificate,
+ Error
+} validate_result;
+
+static validate_result
+ssl_matches_common_name(const char *hostname, const X509 *server_cert)
+{
+ int common_name_loc = -1;
+ X509_NAME_ENTRY *common_name_entry = NULL;
+ ASN1_STRING *common_name_asn1 = NULL;
+ char *common_name_str = NULL;
+
+ // Find the position of the CN field in the Subject field of the certificate
+ common_name_loc = X509_NAME_get_index_by_NID(X509_get_subject_name((X509 *) server_cert), NID_commonName, -1);
+ if (common_name_loc < 0) {
+ return Error;
+ }
+
+ // Extract the CN field
+ common_name_entry = X509_NAME_get_entry(X509_get_subject_name((X509 *) server_cert), common_name_loc);
+ if (common_name_entry == NULL) {
+ return Error;
+ }
+
+ // Convert the CN field to a C string
+ common_name_asn1 = X509_NAME_ENTRY_get_data(common_name_entry);
+ if (common_name_asn1 == NULL) {
+ return Error;
+ }
+ common_name_str = (char *) ASN1_STRING_data_compat(common_name_asn1);
+
+ // Make sure there isn't an embedded NUL character in the CN
+ if ((size_t) ASN1_STRING_length(common_name_asn1) != strlen(common_name_str)) {
+ return MalformedCertificate;
+ }
+
+ // Compare expected hostname with the CN
+ if (strcasecmp(hostname, common_name_str) == 0) {
+ return MatchFound;
+ } else {
+ return MatchNotFound;
+ }
+}
+
+static validate_result
+ssl_matches_subject_alternative_name(const char *hostname, const X509 *server_cert)
+{
+ validate_result result = MatchNotFound;
+ int i;
+ int san_names_nb = -1;
+ STACK_OF(GENERAL_NAME) *san_names = NULL;
+
+ // Try to extract the names within the SAN extension from the certificate
+ san_names = X509_get_ext_d2i((X509 *) server_cert, NID_subject_alt_name, NULL, NULL);
+ if (san_names == NULL) {
+ return NoSANPresent;
+ }
+ san_names_nb = sk_GENERAL_NAME_num(san_names);
+
+ // Check each name within the extension
+ for (i = 0; i < san_names_nb; i++) {
+ const GENERAL_NAME *current_name = sk_GENERAL_NAME_value(san_names, i);
+
+ if (current_name->type == GEN_DNS) {
+ // Current name is a DNS name, let's check it
+ char *dns_name = (char *) ASN1_STRING_data_compat(current_name->d.dNSName);
+
+ // Make sure there isn't an embedded NUL character in the DNS name
+ if ((size_t) ASN1_STRING_length(current_name->d.dNSName) != strlen(dns_name)) {
+ result = MalformedCertificate;
+ break;
+ } else {
+ // Compare expected hostname with the DNS name
+ if (strcasecmp(hostname, dns_name) == 0) {
+ result = MatchFound;
+ break;
+ }
+ }
+ }
+ }
+ sk_GENERAL_NAME_pop_free(san_names, GENERAL_NAME_free);
+
+ return result;
+}
+
+bool
+ssl_validate_hostname(const char *hostname, const X509 *server_cert)
+{
+ validate_result result;
+
+ if ((hostname == NULL) || (server_cert == NULL)) {
+ return false;
+ }
+
+ // First try the Subject Alternative Names extension
+ result = ssl_matches_subject_alternative_name(hostname, server_cert);
+ if (result == NoSANPresent) {
+ // Extension was not found: try the Common Name
+ result = ssl_matches_common_name(hostname, server_cert);
+ }
+
+ return result == MatchFound;
+}
+
+#endif /* HAVE_SSL */
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