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net/dns: set IPv4 auto mode in NM, so it lets us set DNS.

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Part of #1870.

Signed-off-by: David Anderson <danderson@tailscale.com>
(cherry picked from commit 7d16c8228b)
This commit is contained in:
David Anderson 2021-05-06 14:43:04 -07:00
parent bf7c50dbdd
commit 71bcaae29e
1 changed files with 22 additions and 12 deletions
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34
net/dns/nm.go
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@ -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)