netsh: Clear existing IPv6 DNS servers before configuring new ones

When there are no IPv6 DNS published, the adapter state is not
sanitized and might contain IPv6 DNS server from a previous session.

netsh_ifconfig_options() clears DNS servers for IPv4 already.

Signed-off-by: Simon Rozman <simon@rozman.si>
Acked-by: Lev Stipakov <lstipakov@gmail.com>
Message-Id: <20200924064452.1001-2-simon@rozman.si>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg21078.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

diff --git a/src/openvpn/tun.c b/src/openvpn/tun.c
index 8fd3229f161d06175a0df47c1e976f1b05c94e62..b1cd7a1b5ec4aa20c294596489299918a4ed23ba 100644 (file)
--- a/src/openvpn/tun.c
+++ b/src/openvpn/tun.c
@@ -5281,7 +5281,6 @@ ip_addr_member_of(const in_addr_t addr, const IP_ADDR_STRING *ias)
  * Set the ipv6 dns servers on the specified interface.
  * The list of dns servers currently set on the interface
  * are cleared first.
- * No action is taken if number of addresses (addr_len) < 1.
  */
 static void
 netsh_set_dns6_servers(const struct in6_addr *addr_list,
@@ -5291,6 +5290,13 @@ netsh_set_dns6_servers(const struct in6_addr *addr_list,
     struct gc_arena gc = gc_new();
     struct argv argv = argv_new();
 
+    /* delete existing DNS settings from TAP interface */
+    argv_printf(&argv, "%s%s interface ipv6 delete dns %lu all",
+                get_win_sys_path(),
+                NETSH_PATH_SUFFIX,
+                adapter_index);
+    netsh_command(&argv, 2, M_FATAL);
+
     for (int i = 0; i < addr_len; ++i)
     {
         const char *fmt = (i == 0) ?