Also announce IV_CIPHERS as client in OpenVPN 2.4

This improves compatbility to a OpenVPN 2.5 server and
allows to negotiate a different cipher than AES-128/256-GCM
without abusing the poor man's NCP support with --cipher.

We keep the IV_NCP=2 flag logic as broken as it is since 2.5 server
ignore the flag if IV_CIPHERS is set and this might break existing
2.4 setups.

Server support for IV_CIPHERS is not added since it would be quite
intrusive and users should rather upgrade to 2.5 on the server
if they want the full benefits.

This commit cherry picks a few parts of
868b200c3aef6ee5acfdf679770832018ebc7b70

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20200830140736.16571-3-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg20844.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

diff --git a/src/openvpn/init.c b/src/openvpn/init.c
index 9142ba5192c547d0f484df3a894fe4070bf03e0c..f35bf9c2b8d5a1513dc2c3bf913a044bb54ccd91 100644 (file)
--- a/src/openvpn/init.c
+++ b/src/openvpn/init.c
@@ -2745,6 +2745,7 @@ do_init_crypto_tls(struct context *c, const unsigned int flags)
     to.tcp_mode = link_socket_proto_connection_oriented(options->ce.proto);
     to.config_ciphername = c->c1.ciphername;
     to.config_authname = c->c1.authname;
+    to.config_ncp_ciphers = options->ncp_ciphers;
     to.ncp_enabled = options->ncp_enabled;
     to.transition_window = options->transition_window;
     to.handshake_window = options->handshake_window;

diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c
index dd9c52fb2de05f768d2995a7daabed5730c77539..c93beea6730be4fcabc6fe2ec3040d24f9cb97c2 100644 (file)
--- a/src/openvpn/ssl.c
+++ b/src/openvpn/ssl.c
@@ -2311,7 +2311,17 @@ push_peer_info(struct buffer *buf, struct tls_session *session)
         if (session->opt->ncp_enabled
             && (session->opt->mode == MODE_SERVER || session->opt->pull))
         {
+            /* We keep announcing IV_NCP=2 in OpenVPN 2.4 even though it is
+             * technically wrong to ensure not to break 2.4 setups on a
+             * minor release */
             buf_printf(&out, "IV_NCP=2\n");
+            buf_printf(&out, "IV_CIPHERS=%s", session->opt->config_ncp_ciphers);
+            if (!tls_item_in_cipher_list(session->opt->config_ciphername,
+                                         session->opt->config_ncp_ciphers))
+            {
+                buf_printf(&out, ":%s", session->opt->config_ciphername);
+            }
+            buf_printf(&out, "\n");
         }
 
         /* push compression status */

diff --git a/src/openvpn/ssl_common.h b/src/openvpn/ssl_common.h
index ac25ffa78c0145b1a2b26d5620aa35b89d85b435..378b81fdce06abb8b0c7ea68c8b2a0cd3ba83f78 100644 (file)
--- a/src/openvpn/ssl_common.h
+++ b/src/openvpn/ssl_common.h
@@ -286,6 +286,7 @@ struct tls_options
 
     const char *config_ciphername;
     const char *config_authname;
+    const char *config_ncp_ciphers;
     bool ncp_enabled;
 
     /** TLS handshake wrapping state */