Correctly calculate packet id size when epoch packet format is in use

The code assumed that always when tls mode (without CFB/OFB) is in use
that the packet size is 4 bytes. With epoch packet format is incorrect
as that uses 64 bit.

Even thought packet_id_long_form has a the same size (8 byte) it is not
the same header format (32 bit time + 32 bit IV) as the epoch
format (16 bit epoch + 48 IV). Use a simple sizeof(uint64_t) to
avoid suggesting that it might be the same.

Github: closes OpenVPN/openvpn#1074

Change-Id: I5b862eabe032eb4d2229ff5b2f4f6af7406f6f4e
Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Antonio Quartulli <antonio@mandelbit.com>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1829
Message-Id: <20260729064158.15731-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg37983.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

diff --git a/src/openvpn/mtu.c b/src/openvpn/mtu.c
index e5db8ab135d55c8170f110e634cf619fb98c5b07..f3c2874870b17ffc57d5a65194bd002af0273ceb 100644 (file)
--- a/src/openvpn/mtu.c
+++ b/src/openvpn/mtu.c
@@ -35,6 +35,7 @@
 #include "crypto.h"
 
 #include "memdbg.h"
+#include "ssl_common.h"
 
 /* allocate a buffer for socket or tun layer */
 void
@@ -51,6 +52,13 @@ unsigned int
 calc_packet_id_size_dc(const struct options *options, const struct key_type *kt)
 {
     bool tlsmode = options->tls_server || options->tls_client;
+    bool epoch = options->imported_protocol_flags & CO_EPOCH_DATA_KEY_FORMAT;
+
+    /* epoch format uses a 64-bit packet id: 16 bit epoch + 48 bit per-epoch counter */
+    if (epoch)
+    {
+        return sizeof(uint64_t);
+    }
 
     bool packet_id_long_form = !tlsmode || cipher_kt_mode_ofb_cfb(kt->cipher);