Disable DCO if proxy is set via management

Commit

    45a1cb2 ("Disable DCO if proxy is set via management")

attempted to disable DCO when proxy is set via management interface. However,
at least on Windows this doesn't work, since:

 - setting tuntap_options->disable_dco to true is not enough to disable DCO
 - at this point it is a bit too late, since we've already done DCO-specific
   adjustments

Since proxy can be set via management only if --management-query-proxy is
specified, the better way is to add a check to dco_check_startup_option().

Github: fixes #522

Change-Id: I16d6a9fefa317d7d4a195e786618328445bdbca8
Signed-off-by: Lev Stipakov <lev@openvpn.net>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20240318181744.20625-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg28415.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

src/openvpn/dco.c

@@ -387,6 +387,12 @@ dco_check_startup_option(int msglevel, const struct options *o)
         return false;
     }
 
+    if (o->management_flags & MF_QUERY_PROXY)
+    {
+        msg(msglevel, "Note: --management-query-proxy disables data channel offload.");
+        return false;
+    }
+
     /* now that all options have been confirmed to be supported, check
      * if DCO is truly available on the system
      */

src/openvpn/init.c

@@ -221,12 +221,6 @@ management_callback_proxy_cmd(void *arg, const char **p)
     }
     else if (p[2] && p[3])
     {
-        if (dco_enabled(&c->options))
-        {
-            msg(M_INFO, "Proxy set via management, disabling Data Channel Offload.");
-            c->options.tuntap_options.disable_dco = true;
-        }
-
         if (streq(p[1], "HTTP"))
         {
             struct http_proxy_options *ho;