Fix logic when pushed cipher triggers tun reopen and ignore more options

The logic was inverted. Only when link-mtu is used, pushing a cipher can
change the MTU and not the other way round. (found by zeropath)

Also ignore a few more options that should not trigger a reopen of tun
in push message.

Reported-by: Joshua Rogers <[email protected]>
Found-by: ZeroPath (https://zeropath.com/)

Change-Id: I76eb584024610a6054a069340adbac988abf686c
Signed-off-by: Arne Schwabe <[email protected]>
Acked-by: Gert Doering <[email protected]>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1321
Message-Id: <[email protected]>
URL: https://www.mail-archive.com/[email protected]/msg33989.html
Signed-off-by: Gert Doering <[email protected]>

Author: schwabe

src/openvpn/push.c

@@ -1029,15 +1029,25 @@ push_update_digest(md_ctx_t *ctx, struct buffer *buf, const struct options *opt)
     char line[OPTION_PARM_SIZE];
     while (buf_parse(buf, ',', line, sizeof(line)))
     {
-        /* peer-id and auth-token might change on restart and this should not trigger reopening tun
+        /* peer-id and auth-token might change on restart and this should not
+         * trigger reopening tun
+         * Also other options that only affect the control channel should
+         * not trigger a reopen of the tun device
          */
-        if (strprefix(line, "peer-id ") || strprefix(line, "auth-token ")
-            || strprefix(line, "auth-token-user "))
+        if (strprefix(line, "peer-id ")
+            || strprefix(line, "auth-token ")
+            || strprefix(line, "auth-token-user")
+            || strprefix(line, "protocol-flags ")
+            || strprefix(line, "key-derivation ")
+            || strprefix(line, "explicit-exit-notify ")
+            || strprefix(line, "ping ")
+            || strprefix(line, "ping-restart ")
+            || strprefix(line, "ping-timer "))
         {
             continue;
         }
         /* tun reopen only needed if cipher change can change tun MTU */
-        if (strprefix(line, "cipher ") && !opt->ce.tun_mtu_defined)
+        if (strprefix(line, "cipher ") && opt->ce.tun_mtu_defined)
         {
             continue;
         }