[Openvpn-devel] [PATCH] Only announce IV_NCP=2 when we are willing to support these ciphers

[Arne Schwabe]

We currently always announce IV_NCP=2 when we support these ciphers even
when we do not accept them. This lead to a server pushing a AES-GCM-128
cipher to clients and the client then rejecting it.
---
 src/openvpn/init.c       | 1 +
 src/openvpn/openvpn.h    | 1 +
 src/openvpn/options.c    | 7 +++++++
 src/openvpn/ssl.c        | 4 +++-
 src/openvpn/ssl_common.h | 1 +
 5 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/openvpn/init.c b/src/openvpn/init.c
index b5a034dc..32f7bc7a 100644
--- a/src/openvpn/init.c
+++ b/src/openvpn/init.c
@@ -2795,6 +2795,7 @@ 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 = c->c1.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/openvpn.h b/src/openvpn/openvpn.h
index 29d21f0a..1fdbfe3c 100644
--- a/src/openvpn/openvpn.h
+++ b/src/openvpn/openvpn.h
@@ -208,6 +208,7 @@ struct context_1
 
     const char *ciphername;     /**< Data channel cipher from config file */
     const char *authname;       /**< Data channel auth from config file */
+    const char *ncp_ciphers;    /**< NCP Ciphers */
     int keysize;                /**< Data channel keysize from config file */
 #endif
 };
diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index c84b9d5e..cb25db5b 100644
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -7687,6 +7687,13 @@ add_option(struct options *options,
     {
         VERIFY_PERMISSION(OPT_P_GENERAL|OPT_P_INSTANCE);
         options->ncp_ciphers = p[1];
+
+        if (!(tls_item_in_cipher_list("AES-128-GCM", options->ncp_ciphers)
+              && tls_item_in_cipher_list("AES-256-GCM", options->ncp_ciphers)))
+        {
+            msg(M_INFO, "Not including AES-128-GCM and AES-256-GCM in 
ncp-ciphers "
+                "disables announcing NCP support with IV_NCP=2");
+        }
     }
     else if (streq(p[0], "ncp-disable") && !p[1])
     {
diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c
index d5833ac6..f1719303 100644
--- a/src/openvpn/ssl.c
+++ b/src/openvpn/ssl.c
@@ -2327,7 +2327,9 @@ push_peer_info(struct buffer *buf, struct tls_session 
*session)
 
         /* support for Negotiable Crypto Parameters */
         if (session->opt->ncp_enabled
-            && (session->opt->mode == MODE_SERVER || session->opt->pull))
+            && (session->opt->mode == MODE_SERVER || session->opt->pull)
+            && tls_item_in_cipher_list("AES-128-GCM", 
session->opt->config_ncp_ciphers)
+            && tls_item_in_cipher_list("AES-256-GCM", 
session->opt->config_ncp_ciphers))
         {
             buf_printf(&out, "IV_NCP=2\n");
         }
diff --git a/src/openvpn/ssl_common.h b/src/openvpn/ssl_common.h
index 0312c1f8..133c3c22 100644
--- a/src/openvpn/ssl_common.h
+++ b/src/openvpn/ssl_common.h
@@ -290,6 +290,7 @@ struct tls_options
 
     const char *config_ciphername;
     const char *config_authname;
+    const char *config_ncp_ciphers;
     bool ncp_enabled;
 
     bool tls_crypt_v2;
-- 
2.22.0



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