[Openvpn-devel,6/8] Cleanup: Remove special case code for old poor man's NCP.

Message ID 20200709101603.11941-6-arne@rfc2549.org
State Accepted
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  • [Openvpn-devel,1/8] Deprecate ncp-disable and add improved ncp to Changes.rst
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Commit Message

Arne Schwabe July 9, 2020, 10:16 a.m.
Ever since the NCPv2 the ncp_get_best_cipher uses the global
options->ncp_enabled option and ignore the tls_session->ncp_enabled

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
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>
 src/openvpn/init.c |  2 ++
 src/openvpn/ssl.c  | 21 +++++++--------------
 2 files changed, 9 insertions(+), 14 deletions(-)


Gert Doering July 10, 2020, 4:51 p.m. | #1
Acked-by: Gert Doering <gert@greenie.muc.de>

Tested on client and server side (and server vs. 2.3/2.4/master clients)
and all works, including --ncp-disable clients.  I'm fairly sure I have
not all corner cases covered (like, master client talking to a 2.3 server
with poor man's NCP), so more testing is needed in the 2.5-beta phase...

Your patch has been applied to the master branch.

commit e539c95dc8d240327be17e8647e52556dd7fd92d
Author: Arne Schwabe
Date:   Thu Jul 9 12:16:01 2020 +0200

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

     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>

kind regards,

Gert Doering


diff --git a/src/openvpn/init.c b/src/openvpn/init.c
index 91b919d5..e9c01629 100644
--- 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 f3fe0ecf..668bcbd9 100644
--- a/src/openvpn/ssl.c
+++ b/src/openvpn/ssl.c
@@ -1986,6 +1986,12 @@  tls_session_update_crypto_params(struct tls_session *session,
             options->keysize = 0;
+    else
+    {
+      /* Very hacky workaround and quick fix for our calculation
+       * not correct to avoid a regression */
+        return tls_session_generate_data_channel_keys(session);
+    }
     init_key_type(&session->opt->key_type, options->ciphername,
                   options->authname, options->keysize, true, true);
@@ -2463,8 +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)
@@ -2616,18 +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 */