Cleanup: Remove special case code for old poor man's NCP.

Ever since the NCPv2 the ncp_get_best_cipher uses the global
options->ncp_enabled option and ignore the tls_session->ncp_enabled
option.

The server side's poor man's NCP is implemented as seeing the list
of supported ciphers from the peer as just one cipher so this special
handling for poor man's NCP of the older NCP here is not needed anymore.

Theoretically we can now get rid of tls_session->ncp_enabled but doing
so requires more refactoring since options is not available in the
methods that still use it. And when we remove ncp-disable the variable
will be removed anyway.

This commit moves the data channel key generation for the corner case of a
client not supporting NCP but having the same cipher as the server to
the same function that also generates data channel keys for NCP and
poort man's NCP.

This has an unintended side effect of changing the calculated frame
size for this special case. The old path did call
tls_session_update_crypto_params.
To avoid this change in behaviour, this patch adds a hacky
workaround for this.

A proper solution for this needs still be found but this allows the patch
set to be merged.

Document the remaining usage of tls_poor_mans_ncp better.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20200709101603.11941-6-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg20251.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

diff --git a/src/openvpn/init.c b/src/openvpn/init.c
index 91b919d5af656b8db74bcd5a57ae9cd7f85fe4ca..e9c016291d854e9f768083b1d5a7a21d0711c441 100644 (file)
--- a/src/openvpn/init.c
+++ b/src/openvpn/init.c
@@ -2376,6 +2376,8 @@ do_deferred_options(struct context *c, const unsigned int found)
         }
         else if (c->options.ncp_enabled)
         {
+            /* If the server did not push a --cipher, we will switch to the
+             * remote cipher if it is in our ncp-ciphers list */
             tls_poor_mans_ncp(&c->options, c->c2.tls_multi->remote_ciphername);
         }
         struct frame *frame_fragment = NULL;

diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c
index 3420b0dd593be46cc3a6fa703df9a7c934a826b6..54a2301133f187782f66865bd92636a2b1bdce0d 100644 (file)
--- a/src/openvpn/ssl.c
+++ b/src/openvpn/ssl.c
@@ -1985,6 +1985,13 @@ tls_session_update_crypto_params(struct tls_session *session,
             options->keysize = 0;
         }
     }
+    else
+    {
+      /* Very hacky workaround and quick fix for frame calculation
+       * different when adjusting frame size when the original and new cipher
+       * are identical to avoid a regression with client without NCP */
+        return tls_session_generate_data_channel_keys(session);
+    }
 
     init_key_type(&session->opt->key_type, options->ciphername,
                   options->authname, options->keysize, true, true);
@@ -2462,8 +2469,7 @@ key_method_2_write(struct buffer *buf, struct tls_session *session)
      * generation is postponed until after the pull/push, so we can process pushed
      * cipher directives.
      */
-    if (session->opt->server && !(session->opt->ncp_enabled
-                                  && session->opt->mode == MODE_SERVER && ks->key_id <= 0))
+    if (session->opt->server && !(session->opt->mode == MODE_SERVER && ks->key_id <= 0))
     {
         if (ks->authenticated > KS_AUTH_FALSE)
         {
@@ -2615,18 +2621,6 @@ key_method_2_read(struct buffer *buf, struct tls_multi *multi, struct tls_sessio
     multi->remote_ciphername =
         options_string_extract_option(options, "cipher", NULL);
 
-    if (!tls_peer_supports_ncp(multi->peer_info))
-    {
-        /* Peer does not support NCP, but leave NCP enabled if the local and
-         * remote cipher do not match to attempt 'poor-man's NCP'.
-         */
-        if (multi->remote_ciphername == NULL
-            || 0 == strcmp(multi->remote_ciphername, multi->opt.config_ciphername))
-        {
-            session->opt->ncp_enabled = false;
-        }
-    }
-
     if (tls_session_user_pass_enabled(session))
     {
         /* Perform username/password authentication */