client confirm server hostname in cert

Openssl v1.0.2 and above have support for checking the hostname
the client side connected to against the hostname on the cert the
server presented.

This enables that feature if the necessary API is available in the
openssl version, meaning the connection will fail at ssl negotiation if the
cert isn't for the requested server

It's very easy to test, add a fake entry to /etc/hosts for the server IP with
a different name, using that will fail at ssl but using the correct dns name
matching the certificate will work.

CMakeLists.txt

@@ -943,6 +943,7 @@ endforeach()
 set (temp ${CMAKE_REQUIRED_LIBRARIES})
 set(CMAKE_REQUIRED_LIBRARIES ${LIB_LIST})
 CHECK_FUNCTION_EXISTS(SSL_CTX_set1_param LWS_HAVE_SSL_CTX_set1_param)
+CHECK_FUNCTION_EXISTS(X509_VERIFY_PARAM_set1_host LWS_HAVE_X509_VERIFY_PARAM_set1_host)
 set(CMAKE_REQUIRED_LIBRARIES ${temp})
 # Generate the lws_config.h that includes all the public compilation settings.
 configure_file(

lib/private-libwebsockets.h

@@ -221,6 +221,7 @@ static inline int compatible_close(int fd) { return close(fd); }
 #ifdef LWS_HAVE_OPENSSL_ECDH_H
 #include <openssl/ecdh.h>
 #endif
+#include <openssl/x509v3.h>
 #endif /* not USE_MBEDTLS */
 #endif /* not USE_POLARSSL */
 #endif /* not USE_WOLFSSL */

lib/ssl-client.c

@@ -38,11 +38,24 @@ lws_ssl_client_bio_create(struct lws *wsi)
 #if defined(LWS_USE_MBEDTLS)
 #else
 	struct lws_context *context = wsi->context;
-#if defined(CYASSL_SNI_HOST_NAME) || defined(WOLFSSL_SNI_HOST_NAME) || defined(SSL_CTRL_SET_TLSEXT_HOSTNAME)
 	const char *hostname = lws_hdr_simple_ptr(wsi, _WSI_TOKEN_CLIENT_HOST);
-#endif
+	X509_VERIFY_PARAM *param;
+
+	(void)hostname;
+	(void)param;
 
 	wsi->ssl = SSL_new(wsi->vhost->ssl_client_ctx);
+
+#if defined LWS_HAVE_X509_VERIFY_PARAM_set1_host
+	param = SSL_get0_param(wsi->ssl);
+	/* Enable automatic hostname checks */
+	X509_VERIFY_PARAM_set_hostflags(param,
+					X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS);
+	X509_VERIFY_PARAM_set1_host(param, hostname, 0);
+	/* Configure a non-zero callback if desired */
+	SSL_set_verify(wsi->ssl, SSL_VERIFY_PEER, 0);
+#endif
+
 #ifndef USE_WOLFSSL
 	SSL_set_mode(wsi->ssl,  SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER);
 #endif

lws_config.h.in

@@ -82,6 +82,7 @@
 /* SSL server using ECDH certificate */
 #cmakedefine LWS_SSL_SERVER_WITH_ECDH_CERT
 #cmakedefine LWS_HAVE_SSL_CTX_set1_param
+#cmakedefine LWS_HAVE_X509_VERIFY_PARAM_set1_host
 
 /* CGI apis */
 #cmakedefine LWS_WITH_CGI