Add SSL certificate verification support and enable it by default

Disable SSL certificate verification with -z/--no-check-certificate

cmdline.c

@@ -64,6 +64,9 @@ void cmdline_parser_print_help (void) {
 #endif
 "\n"
 "Additional options for specific features:\n"
+#ifdef USE_SSL
+" -z, --no-check-certficate Don't verify server SSL certificate\n"
+#endif
 " -F, --passfile=STRING     File with credentials for proxy authentication\n"
 " -P, --proxyauth=STRING    Proxy auth credentials user:pass combination\n"
 " -R, --remproxyauth=STRING Remote proxy auth credentials user:pass combination\n"
@@ -165,6 +168,7 @@ int cmdline_parser( int argc, char * const *argv, struct gengetopt_args_info *ar
 	args_info->proctitle_arg = NULL; \
 	args_info->enforcetls1_flag = 0; \
 	args_info->host_arg = NULL; \
+	args_info->no_check_cert_flag = 0; \
 }
 
 	clear_args();
@@ -209,12 +213,13 @@ int cmdline_parser( int argc, char * const *argv, struct gengetopt_args_info *ar
 			{ "encrypt-proxy",	0, NULL, 'E' },
 			{ "encrypt-remproxy",0,NULL, 'X' },
 			{ "no-ssl3",		0, NULL, 'T' },
+			{ "no-check-certificate",0,NULL,'z' },
 			{ NULL,				0, NULL, 0 }
 		};
 
-		c = getopt_long (argc, argv, "hVia:u:s:t:F:p:P:r:R:d:H:x:nvNeEXqLo:T", long_options, &option_index);
+		c = getopt_long (argc, argv, "hVia:u:s:t:F:p:P:r:R:d:H:x:nvNeEXqLo:Tz", long_options, &option_index);
 #else
-		c = getopt( argc, argv, "hVia:u:s:t:F:p:P:r:R:d:H:x:nvNeEXqLo:T" );
+		c = getopt( argc, argv, "hVia:u:s:t:F:p:P:r:R:d:H:x:nvNeEXqLo:Tz" );
 #endif
 
 		if (c == -1)
@@ -431,6 +436,12 @@ int cmdline_parser( int argc, char * const *argv, struct gengetopt_args_info *ar
 				args_info->quiet_flag = !(args_info->quiet_flag);
 				break;
 
+			case 'z':	/* Don't verify server SSL certificate */
+				args_info->no_check_cert_flag = 1;
+				if( args_info->verbose_flag )
+					message("Server SSL certificate verification disabled\n");
+				break;
+
 			case 0:	/* Long option with no short option */
 
 			case '?':	/* Invalid option.  */

cmdline.h

@@ -51,6 +51,7 @@ struct gengetopt_args_info {
 	char *proctitle_arg;	/* Override process title (default=off). */
 	int enforcetls1_flag;    /* Override default and enforce TLSv1 */
 	char *host_arg;         /* Optional Host Header */
+	int no_check_cert_flag;	/* Turn off server SSL certificate verification (default=on) */
 	int help_given;			/* Whether help was given. */
 	int version_given;		/* Whether version was given. */
 	int user_given;			/* Whether user was given. */

docs/proxytunnel.1.adoc

@@ -52,6 +52,12 @@ also be used for other proxy-traversing purposes like proxy bouncing.
 *-T*, *--no-ssl3*::
     Prevent the use of SSLv3 in encrypted connections (default: enabled)
 
+*-z*, *--no-check-certificate*::
+    Do not verify server SSL certificate when establishing an SSL connection.
+    By default, the server SSL certficate is verified and the target host name
+    is checked against the server certificate's subject alternative names if
+    any are present, or common name if there are no subject alternative names.
+
 *-F*, *--passfile*=_filename_::
     Use _filename_ for reading username and password for HTTPS proxy
     authentication, the file uses the same format as .wgetrc and can be shared

http.c

@@ -159,7 +159,7 @@ void proxy_protocol(PTSTREAM *pts) {
 
 /* If --encrypt-remproxy is specified, connect to the remote proxy using SSL */
 	if ( args_info.encryptremproxy_flag )
-		stream_enable_ssl(stunnel);
+		stream_enable_ssl(stunnel, args_info.remproxy_arg);
 
 		if( args_info.verbose_flag )
 			message( "\nTunneling to %s (destination)\n", args_info.dest_arg );

proxytunnel.c

@@ -265,7 +265,7 @@ void do_daemon()
 #ifdef USE_SSL
 			/* If --encrypt-proxy is specified, connect to the proxy using SSL */
 			if ( args_info.encryptproxy_flag )
-				stream_enable_ssl(stunnel);
+				stream_enable_ssl(stunnel, args_info.proxy_arg);
 #endif /* USE_SSL */
 
 			/* Open the tunnel */
@@ -274,7 +274,7 @@ void do_daemon()
 #ifdef USE_SSL
 			/* If --encrypt is specified, wrap all traffic after the proxy handoff in SSL */
 			if( args_info.encrypt_flag )
-				stream_enable_ssl(stunnel);
+				stream_enable_ssl(stunnel, args_info.dest_arg);
 #endif /* USE_SSL */
 
 #ifdef SETPROCTITLE
@@ -387,7 +387,7 @@ int main( int argc, char *argv[] ) {
 		/* If --encrypt-proxy is specified, connect to the proxy using SSL */
 #ifdef USE_SSL
 		if ( args_info.encryptproxy_flag )
-			stream_enable_ssl(stunnel);
+			stream_enable_ssl(stunnel, args_info.proxy_arg);
 #endif /* USE_SSL */
 
 		/* Open the tunnel */
@@ -396,7 +396,7 @@ int main( int argc, char *argv[] ) {
 		/* If --encrypt is specified, wrap all traffic after the proxy handoff in SSL */
 #ifdef USE_SSL
 		if( args_info.encrypt_flag )
-			stream_enable_ssl(stunnel);
+			stream_enable_ssl(stunnel, args_info.dest_arg);
 #endif /* USE_SSL */
 
 #ifdef SETPROCTITLE

ptstream.c

@@ -19,6 +19,8 @@
 
 /* ptstream.c */
 
+#include <arpa/inet.h>
+#include <openssl/x509v3.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -142,15 +144,109 @@ int stream_copy(PTSTREAM *pts_from, PTSTREAM *pts_to) {
 }
 
 
+/* Check the certificate host name against the expected host name */
+/* Return 1 if peer hostname is valid, any other value indicates failure */
+int check_cert_valid_host(const char *cert_host, const char *peer_host) {
+	if (cert_host == NULL || peer_host == NULL) {
+		return 0;
+	}
+	if (cert_host[0] == '*') {
+		if (strncmp(cert_host, "*.", 2) != 0) {
+			/* Invalid wildcard hostname */
+			return 0;
+		}
+		/* Skip "*." */
+		cert_host += 2;
+		/* Wildcards can only match the first subdomain component */
+		while (*peer_host++ != '.' && *peer_host != '\0')
+			;;
+	}
+	if (strlen(cert_host) == 0 || strlen(peer_host) == 0) {
+		return 0;
+	}
+	return strcmp(cert_host, peer_host) == 0;
+}
+
+
+int check_cert_valid_ip6(const unsigned char *cert_ip_data, const int cert_ip_len, const struct in6_addr *addr6) {
+	int i;
+	for (i = 0; i < cert_ip_len; i++) {
+		if (cert_ip_data[i] != addr6->s6_addr[i]) {
+			return 0;
+		}
+	}
+	return 1;
+}
+
+
+int check_cert_valid_ip(const unsigned char *cert_ip_data, const int cert_ip_len, const struct in_addr *addr) {
+	int i;
+	for (i = 0; i < cert_ip_len; i++) {
+		if (cert_ip_data[i] != ((addr->s_addr >> (i * 8)) & 0xFF)) {
+			return 0;
+		}
+	}
+	return 1;
+}
+
+
+int check_cert_names(X509 *cert, char *peer_host) {
+	char peer_cn[256];
+	const GENERAL_NAME *gn;
+	STACK_OF(GENERAL_NAME) *gen_names;
+	struct in_addr addr;
+	struct in6_addr addr6;
+	int peer_host_is_ipv4 = 0, peer_host_is_ipv6 = 0;
+	int i, san_count;
+
+	gen_names = X509_get_ext_d2i(cert, NID_subject_alt_name, NULL, NULL);
+	san_count = sk_GENERAL_NAME_num(gen_names);
+	if (san_count > 0) {
+		peer_host_is_ipv4 = (inet_pton(AF_INET, peer_host, &addr) == 1);
+		peer_host_is_ipv6 = (peer_host_is_ipv4 ? 0 : inet_pton(AF_INET6, peer_host, &addr6) == 1);
+		for (i = 0; i < san_count; i++) {
+			gn = sk_GENERAL_NAME_value(gen_names, i);
+			if (gn->type == GEN_DNS && !(peer_host_is_ipv4 || peer_host_is_ipv6)) {
+				if (check_cert_valid_host((char*)ASN1_STRING_data(gn->d.ia5), peer_host)) {
+					return 1;
+				}
+			} else if (gn->type == GEN_IPADD) {
+				if (gn->d.ip->length == 4 && peer_host_is_ipv4) {
+					if (check_cert_valid_ip(gn->d.ip->data, gn->d.ip->length, &addr)) {
+						return 1;
+					}
+				} else if (gn->d.ip->length == 16 && peer_host_is_ipv6) {
+					if (check_cert_valid_ip6(gn->d.ip->data, gn->d.ip->length, &addr6)) {
+						return 1;
+					}
+				}
+			}
+		}
+		message("Host name %s does not match certificate subject alternative names\n", peer_host);
+	} else {
+		X509_NAME_get_text_by_NID(X509_get_subject_name(cert), NID_commonName, peer_cn, sizeof(peer_cn));
+		message("Host name %s does not match certificate common name %s or any subject alternative names\n", peer_host, peer_cn);
+		return check_cert_valid_host(peer_cn, peer_host);
+	}
+	return 0;
+}
+
 /* Initiate an SSL handshake on this stream and encrypt all subsequent data */
-int stream_enable_ssl(PTSTREAM *pts) {
+int stream_enable_ssl(PTSTREAM *pts, const char *proxy_arg) {
 #ifdef USE_SSL
 	const SSL_METHOD *meth;
 	SSL *ssl;
 	SSL_CTX *ctx;
 	long res = 1;
 	long ssl_options = 0;
-	
+
+	X509* cert = NULL;
+	const char *ca_dir = "/etc/ssl/certs/"; /* Default cert directory if none given */
+	long vresult;
+	char *peer_host = NULL;
+	char proxy_arg_fmt[32];
+	size_t proxy_arg_len;
+
 	/* Initialise the connection */
 	SSLeay_add_ssl_algorithms();
 	if (args_info.enforcetls1_flag) {
@@ -165,6 +261,14 @@ int stream_enable_ssl(PTSTREAM *pts) {
 		ssl_options |= SSL_OP_NO_SSLv3;
 	}
 	SSL_CTX_set_options (ctx, ssl_options);
+
+	if ( !args_info.no_check_cert_flag ) {
+		if (!SSL_CTX_load_verify_locations(ctx, NULL, ca_dir)) {
+			message("Error loading certificates from %s\n", ca_dir);
+			goto fail;
+		}
+	}
+
 	ssl = SSL_new (ctx);
 	
 	SSL_set_rfd (ssl, stream_get_incoming_fd(pts));
@@ -182,6 +286,42 @@ int stream_enable_ssl(PTSTREAM *pts) {
 	
 	SSL_connect (ssl);
 
+	if ( !args_info.no_check_cert_flag ) {
+		/* Make sure peer presented a certificate */
+		cert = SSL_get_peer_certificate(ssl);
+		if (cert == NULL) {
+			message("No certificate presented\n");
+			goto fail;
+		}
+
+		/* Check that the certificate is valid */
+		vresult = SSL_get_verify_result(ssl);
+		if (vresult != X509_V_OK) {
+			message("Certificate verification failed (%s)\n",
+					X509_verify_cert_error_string(vresult));
+			goto fail;
+		}
+
+		/* Determine the host name we are connecting to */
+		proxy_arg_len = strlen(proxy_arg);
+		if ((peer_host = malloc(proxy_arg_len + 1)) == NULL) {
+			message("Out of memory\n");
+			goto fail;
+		}
+		snprintf( proxy_arg_fmt, sizeof(proxy_arg_fmt), proxy_arg[0] == '[' ? "[%%%zu[^]]]" : "%%%zu[^:]", proxy_arg_len - 1 );
+		if ( sscanf( proxy_arg, proxy_arg_fmt, peer_host ) != 1 ) {
+			goto fail;
+		}
+
+		/* Verify the certificate name matches the host we are connecting to */
+		if (!check_cert_names(cert, peer_host)) {
+			goto fail;
+		}
+
+		free(peer_host);
+		X509_free(cert);
+	}
+
 	/* Store ssl and ctx parameters */
 	pts->ssl = ssl;
 	pts->ctx = ctx;
@@ -190,6 +330,17 @@ int stream_enable_ssl(PTSTREAM *pts) {
 #endif /* USE_SSL */
 
 	return 1;
+
+fail:
+#ifdef USE_SSL
+	if (cert != NULL) {
+		X509_free(cert);
+	}
+	if (peer_host != NULL) {
+		free(peer_host);
+	}
+#endif /* USE_SSL */
+	exit(1);
 }
 
 

ptstream.h

@@ -44,7 +44,7 @@ int stream_close(PTSTREAM *pts);
 int stream_read(PTSTREAM *pts, void *buf, size_t len);
 int stream_write(PTSTREAM *pts, void *buf, size_t len);
 int stream_copy(PTSTREAM *pts_from, PTSTREAM *pts_to);
-int stream_enable_ssl(PTSTREAM *pts);
+int stream_enable_ssl(PTSTREAM *pts, const char *proxy_arg);
 int stream_get_incoming_fd(PTSTREAM *pts);
 int stream_get_outgoing_fd(PTSTREAM *pts);