Fix P2P epoch MTU accounting

P2P NCP stores the negotiated epoch flag in the live TLS options, while the MTU calculator reads imported protocol flags from the main options structure. Synchronize that flag for non-pull point-to-point sessions before calculating dynamic framing, and clear it when a later negotiation does not use epoch data keys. Preserve the normal pull-client path.

Related: #1074
Signed-off-by: Darren Carreras <carrerasdarren@gmail.com>

Author: carrerasdarren-cell

CMakeLists.txt

@@ -842,6 +842,8 @@ if (BUILD_TESTING)
         src/openvpn/crypto_mbedtls.c
         src/openvpn/crypto_openssl.c
         src/openvpn/crypto.c
+        src/openvpn/mss.c
+        src/openvpn/mtu.c
         src/openvpn/otime.c
         src/openvpn/packet_id.c
         src/openvpn/ssl_util.c

src/openvpn/ssl.c

@@ -1651,6 +1651,8 @@ tls_session_update_crypto_params(struct tls_multi *multi, struct tls_session *se
         return false;
     }
 
+    p2p_ncp_update_options(options, session);
+
     /* Import crypto settings that might be set by pull/push */
     session->opt->crypto_flags |= options->imported_protocol_flags;
 

src/openvpn/ssl_ncp.c

@@ -470,6 +470,19 @@ p2p_ncp_set_options(struct tls_multi *multi, struct tls_session *session, const
     }
 }
 
+void
+p2p_ncp_update_options(struct options *options, const struct tls_session *session)
+{
+    if (options->mode != MODE_POINT_TO_POINT || options->pull)
+    {
+        return;
+    }
+
+    options->imported_protocol_flags &= ~CO_EPOCH_DATA_KEY_FORMAT;
+    options->imported_protocol_flags |=
+        session->opt->crypto_flags & CO_EPOCH_DATA_KEY_FORMAT;
+}
+
 void
 p2p_mode_ncp(struct tls_multi *multi, struct tls_session *session)
 {

src/openvpn/ssl_ncp.h

@@ -130,6 +130,12 @@ bool tls_item_in_cipher_list(const char *item, const char *list);
  */
 void p2p_mode_ncp(struct tls_multi *multi, struct tls_session *session);
 
+/**
+ * Copy P2P-negotiated protocol flags needed outside the TLS session into the
+ * main options structure.
+ */
+void p2p_ncp_update_options(struct options *options, const struct tls_session *session);
+
 /**
  * Determines the best common cipher from both peers IV_CIPHER lists. The
  * first cipher from the tls-server that is also in the tls-client IV_CIPHER

tests/unit_tests/openvpn/Makefile.am

@@ -341,6 +341,8 @@ ncp_testdriver_SOURCES = test_ncp.c \
 	$(top_srcdir)/src/openvpn/crypto_mbedtls.c \
 	$(top_srcdir)/src/openvpn/crypto_mbedtls_legacy.c \
 	$(top_srcdir)/src/openvpn/crypto_openssl.c \
+	$(top_srcdir)/src/openvpn/mss.c \
+	$(top_srcdir)/src/openvpn/mtu.c \
 	$(top_srcdir)/src/openvpn/otime.c \
 	$(top_srcdir)/src/openvpn/packet_id.c \
 	$(top_srcdir)/src/openvpn/platform.c \

tests/unit_tests/openvpn/test_ncp.c

@@ -34,6 +34,7 @@
 #include <cmocka.h>
 
 #include "ssl_ncp.c"
+#include "mss.h"
 #include "test_common.h"
 
 /* Defines for use in the tests and the mock parse_line() */
@@ -392,6 +393,51 @@ test_ncp_expand(void **state)
     gc_free(&gc);
 }
 
+static void
+test_p2p_epoch_mssfix_mtu(void **state)
+{
+    struct tls_options tls_options = { .data_epoch_supported = true };
+    struct tls_session session = { .opt = &tls_options };
+    struct tls_multi multi = { 0 };
+    struct options o = { .mode = MODE_POINT_TO_POINT };
+    char peer_info[32];
+
+    snprintf(peer_info, sizeof(peer_info), "IV_PROTO=%u",
+             IV_PROTO_DATA_V2 | IV_PROTO_NCP_P2P | IV_PROTO_DATA_EPOCH);
+    multi.peer_info = peer_info;
+
+    p2p_ncp_set_options(&multi, &session, "AES-256-GCM");
+    assert_true(session.opt->crypto_flags & CO_EPOCH_DATA_KEY_FORMAT);
+    p2p_ncp_update_options(&o, &session);
+    assert_true(o.imported_protocol_flags & CO_EPOCH_DATA_KEY_FORMAT);
+
+    o.ce.tun_mtu = 1400;
+    o.ce.mssfix = 1000;
+    o.ce.proto = PROTO_UDP;
+    o.ciphername = "AES-256-GCM";
+    o.authname = "SHA1";
+    o.tls_client = true;
+    o.use_peer_id = true;
+
+    struct key_type kt;
+    init_key_type(&kt, o.ciphername, o.authname, true, false);
+
+    struct frame frame = { 0 };
+    frame_calculate_dynamic(&frame, &kt, &o, NULL);
+
+    /* opcode/peer-id + epoch packet-id + tag + TCP/IP headers */
+    assert_int_equal(frame.mss_fix, 1000 - 4 - 8 - 16 - 40);
+
+    session.opt->crypto_flags &= ~CO_EPOCH_DATA_KEY_FORMAT;
+    p2p_ncp_update_options(&o, &session);
+    assert_false(o.imported_protocol_flags & CO_EPOCH_DATA_KEY_FORMAT);
+
+    o.pull = true;
+    o.imported_protocol_flags |= CO_EPOCH_DATA_KEY_FORMAT;
+    p2p_ncp_update_options(&o, &session);
+    assert_true(o.imported_protocol_flags & CO_EPOCH_DATA_KEY_FORMAT);
+}
+
 
 const struct CMUnitTest ncp_tests[] = {
     cmocka_unit_test(test_check_ncp_ciphers_list),
@@ -400,6 +446,7 @@ const struct CMUnitTest ncp_tests[] = {
     cmocka_unit_test(test_ncp_best),
     cmocka_unit_test(test_ncp_default),
     cmocka_unit_test(test_ncp_expand),
+    cmocka_unit_test(test_p2p_epoch_mssfix_mtu),
 };