Clean up DTLS cipher selection for OpenSSL >= 1.1.0

Where we have SSL_get1_supported_ciphers(), use it to generate the list we
advertise to the server in the first place. This stops us from advertising
DES support when we're not really going to do it, for example.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>

openssl-dtls.c

@@ -680,6 +680,7 @@ void dtls_ssl_free(struct openconnect_info *vpninfo)
 	SSL_free(vpninfo->dtls_ssl);
 }
 
+#if OPENSSL_VERSION_NUMBER < 0x10100000L || defined(LIBRESSL_VERSION_NUMBER)
 void gather_dtls_ciphers(struct openconnect_info *vpninfo, struct oc_text_buf *buf,
 			 struct oc_text_buf *buf12)
 {
@@ -688,11 +689,57 @@ void gather_dtls_ciphers(struct openconnect_info *vpninfo, struct oc_text_buf *b
 	buf_append(buf, "PSK-NEGOTIATE:");
 #endif
 	buf_append(buf, "OC-DTLS1_2-AES256-GCM:OC-DTLS1_2-AES128-GCM:");
+	buf_append(buf12, "ECDHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256:AES128-GCM-SHA256:AES256-GCM-SHA384\r\n");
 #endif
 	buf_append(buf, "DHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA:");
 	buf_append(buf, "AES256-SHA:AES128-SHA:DES-CBC3-SHA:DES-CBC-SHA");
-#ifdef HAVE_DTLS12
-	buf_append(buf12, "ECDHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256:AES128-GCM-SHA256:AES256-GCM-SHA384\r\n");
-#endif
 }
+#else
+void gather_dtls_ciphers(struct openconnect_info *vpninfo, struct oc_text_buf *buf,
+			 struct oc_text_buf *buf12)
+{
+	method_const SSL_METHOD *dtls_method;
+	SSL_CTX *ctx;
+	SSL *ssl;
+	STACK_OF(SSL_CIPHER) *ciphers;
+	int i;
+
+	dtls_method = DTLS_client_method();
+	ctx = SSL_CTX_new(dtls_method);
+	if (!ctx)
+		return;
+	ssl = SSL_new(ctx);
+	if (!ssl) {
+		SSL_CTX_free(ctx);
+		return;
+	}
+
+	ciphers = SSL_get1_supported_ciphers(ssl);
+	for (i = 0; i < sk_SSL_CIPHER_num(ciphers); i++) {
+		const SSL_CIPHER *ciph = sk_SSL_CIPHER_value(ciphers, i);
+		const char *name = SSL_CIPHER_get_name(ciph);
+		const char *vers = SSL_CIPHER_get_version(ciph);
+
+		if (!strcmp(vers, "SSLv3") || !strcmp(vers, "TLSv1.0") ||
+		    !strcmp(vers, "TLSv1/SSLv3")) {
+			buf_append(buf, "%s%s",
+				   (buf_error(buf) || !buf->pos) ? "" : ":",
+				   name);
+		} else if (!strcmp(vers, "TLSv1.2")) {
+			buf_append(buf12, "%s%s:",
+				   (buf_error(buf12) || !buf12->pos) ? "" : ":",
+				   name);
+		}
+	}
+	sk_SSL_CIPHER_free(ciphers);
+	SSL_free(ssl);
+	SSL_CTX_free(ctx);
 
+	/* All DTLSv1 suites are also supported in DTLSv1.2 */
+	if (!buf_error(buf))
+		buf_append(buf12, ":%s", buf->data);
+#ifndef OPENSSL_NO_PSK
+	buf_append(buf, ":PSK-NEGOTIATE");
+#endif
+}
+#endif