net/dns: set IPv4 auto mode in NM, so it lets us set DNS.
Part of
@@ -183,6 +183,25 @@ func (m *nmManager) trySet(ctx context.Context, config OSConfig) error {
// settings here, but that led to #1870.
ipv4Map := settings["ipv4"]
+ // In some versions of NM, you can only provide DNS configuration
+ // if the interface is in "auto" or "manual" mode (defaults to
+ // "disabled").
+ //
+ // In "manual" mode we'd have to also give NM all our IP and
+ // routing configuration, which we don't want to do. So instead,
+ // we set the ipv4 mode to "auto", and then tell it to ignore any
+ // information it might get from DHCP (which is none, since we
+ // don't do DHCP on tailscale0). This is the documented way to
+ // provide only DNS configuration to NetworkManager.
+ //
+ // Some versions of NM don't need this, and will accept DNS
+ // configuration even for disabled interfaces, but there's no harm
+ // in telling those versions to do DHCP and ignore all results,
+ // hence why we have a single codepath here.
+ ipv4Map["method"] = dbus.MakeVariant("auto")
+ ipv4Map["ignore-auto-routes"] = dbus.MakeVariant(true)
+ ipv4Map["ignore-auto-dns"] = dbus.MakeVariant(true)
+ ipv4Map["never-default"] = dbus.MakeVariant(true)
ipv4Map["dns"] = dbus.MakeVariant(dnsv4)
ipv4Map["dns-search"] = dbus.MakeVariant(search)
// We should only request priority if we have nameservers to set.
@@ -202,18 +221,9 @@ func (m *nmManager) trySet(ctx context.Context, config OSConfig) error {
}
ipv6Map := settings["ipv6"]
- // In IPv6 settings, you're only allowed to provide additional
- // static DNS settings in "auto" (SLAAC) or "manual" mode. In
- // "manual" mode you also have to specify IP addresses, so we use
- // "auto".
- //
- // NM actually documents that to set just DNS servers, you should
- // use "auto" mode and then set ignore auto routes and DNS, which
- // basically means "autoconfigure but ignore any autoconfiguration
- // results you might get". As a safety, we also say that
- // NetworkManager should never try to make us the default route
- // (none of its business anyway, we handle our own default
- // routing).
+ // Same logic as above for IPv4 - request autoconfiguration, tell
+ // NM to ignore all autoconfiguration results, and provide manual
+ // DNS settings.
ipv6Map["method"] = dbus.MakeVariant("auto")
if len(addrs6) > 0 {
ipv6Map["address-data"] = dbus.MakeVariant(addrs6)
