Extend push-remove to also handle 'ifconfig'.

Push-remove (introduced in commit 970312f) did not handle "ifconfig"
yet, as both "ifconfig" and "ifconfig-ipv6" are handled differently from
all other pushed options.  Since there was no valid use-case to not-push
"ifconfig" (no support on the client side for running IPv6-only) this
was not an issue so far - but with the recent commits to enable ipv6-only
operation it can be a desirable feature.

The implementation is similar to "push-remove ifconfig-ipv6" - namely,
flagging via a new context option (c->options.push_ifconfig_ipv4_blocked)
and then not creating the push statement in "send_push_reply()".

While not truly elegant, it's much less invasive than the alternatives
(storing the list of "push-remove" statements somewhere and then checking
in push_option_ex())

Trac: #1072

Signed-off-by: Gert Doering <[email protected]>

Acked-by: Antonio Quartulli <[email protected]>
Message-Id: <[email protected]>
URL: https://www.mail-archive.com/[email protected]/msg17169.html
Signed-off-by: Gert Doering <[email protected]>

doc/openvpn.8

@@ -3045,6 +3045,11 @@ an option,
 can be used to first remove the old value, and then add a new
 .B \-\-push
 option with the new value.
+
+NOTE2: due to implementation details, 'ifconfig' and 'ifconfig-ipv6'
+can only be removed with an exact match on the option ("push-remove ifconfig"),
+no substring matching and no matching on the IPv4/IPv6 address argument
+is possible.
 .\"*********************************************************
 .TP
 .B \-\-push\-peer\-info

src/openvpn/options.h

@@ -425,6 +425,7 @@ struct options
     bool push_ifconfig_constraint_defined;
     in_addr_t push_ifconfig_constraint_network;
     in_addr_t push_ifconfig_constraint_netmask;
+    bool push_ifconfig_ipv4_blocked;                    /* IPv4 */
     bool push_ifconfig_ipv6_defined;                    /* IPv6 */
     struct in6_addr push_ifconfig_ipv6_local;           /* IPv6 */
     int push_ifconfig_ipv6_netbits;                     /* IPv6 */

src/openvpn/push.c

@@ -342,7 +342,8 @@ prepare_push_reply(struct context *c, struct gc_arena *gc,
 
     /* ipv4 */
     if (c->c2.push_ifconfig_defined && c->c2.push_ifconfig_local
-        && c->c2.push_ifconfig_remote_netmask)
+        && c->c2.push_ifconfig_remote_netmask
+        && !o->push_ifconfig_ipv4_blocked)
     {
         in_addr_t ifconfig_local = c->c2.push_ifconfig_local;
         if (c->c2.push_ifconfig_local_alias)
@@ -602,6 +603,13 @@ push_remove_option(struct options *o, const char *p)
 {
     msg(D_PUSH_DEBUG, "PUSH_REMOVE searching for: '%s'", p);
 
+    /* ifconfig is special, as not part of the push list */
+    if (streq(p, "ifconfig"))
+    {
+        o->push_ifconfig_ipv4_blocked = true;
+        return;
+    }
+
     /* ifconfig-ipv6 is special, as not part of the push list */
     if (streq( p, "ifconfig-ipv6" ))
     {