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net/dns: add GetBaseConfig to CallbackRouter.

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Allow users of CallbackRouter to supply a GetBaseConfig
implementation. This is expected to be used on Android,
which currently lacks both a) platform support for
Split-DNS and b) a way to retrieve the current DNS
servers.

iOS/macOS also use the CallbackRouter but have platform
support for SplitDNS, so don't need getBaseConfig.

Updates https://github.com/tailscale/tailscale/issues/2116
Updates https://github.com/tailscale/tailscale/issues/988

Signed-off-by: Denton Gentry <dgentry@tailscale.com>
This commit is contained in:
Denton Gentry 2021-10-09 12:17:59 -07:00 committed by Denton Gentry
parent a28d280b95
commit 878a20df29
4 changed files with 17 additions and 31 deletions
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31
ipn/ipnlocal/dnsconfig_test.go
View File

@ -232,32 +232,11 @@ func TestDNSConfigForNetmap(t *testing.T) {
},
},
{
name: "android_does_need_fallbacks",
os: "android",
nm: &netmap.NetworkMap{
DNS: tailcfg.DNSConfig{
FallbackResolvers: []dnstype.Resolver{
{Addr: "8.8.4.4"},
},
Routes: map[string][]dnstype.Resolver{
"foo.com.": {{Addr: "1.2.3.4"}},
},
},
},
prefs: &ipn.Prefs{
CorpDNS: true,
},
want: &dns.Config{
Hosts: map[dnsname.FQDN][]netaddr.IP{},
DefaultResolvers: []dnstype.Resolver{
{Addr: "8.8.4.4:53"},
},
Routes: map[dnsname.FQDN][]dnstype.Resolver{
"foo.com.": {{Addr: "1.2.3.4:53"}},
},
},
},
{
// Prior to fixing https://github.com/tailscale/tailscale/issues/2116,
// Android had cases where it needed FallbackResolvers. This was the
// negative test for the case where Override-local-DNS was set, so the
// fallback resolvers did not need to be used. This test is still valid
// so we keep it, but the fallback test has been removed.
name: "android_does_NOT_need_fallbacks",
os: "android",
nm: &netmap.NetworkMap{

3
ipn/ipnlocal/local.go
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@ -2091,9 +2091,6 @@ func dnsConfigForNetmap(nm *netmap.NetworkMap, prefs *ipn.Prefs, logf logger.Log
addDefault(nm.DNS.FallbackResolvers)
case len(dcfg.Routes) == 0:
// No settings requiring split DNS, no problem.
case versionOS == "android":
// We don't support split DNS at all on Android yet.
addDefault(nm.DNS.FallbackResolvers)
}
return dcfg

12
wgengine/router/callback.go
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@ -18,6 +18,13 @@ type CallbackRouter struct {
SetBoth func(rcfg *Config, dcfg *dns.OSConfig) error
SplitDNS bool
// GetBaseConfigFunc optionally specifies a function to return the current DNS
// config in response to GetBaseConfig.
//
// If nil, reading the current config isn't supported and GetBaseConfig()
// will return ErrGetBaseConfigNotSupported.
GetBaseConfigFunc func() (dns.OSConfig, error)
mu sync.Mutex // protects all the following
rcfg *Config // last applied router config
dcfg *dns.OSConfig // last applied DNS config
@ -50,7 +57,10 @@ func (r *CallbackRouter) SupportsSplitDNS() bool {
}
func (r *CallbackRouter) GetBaseConfig() (dns.OSConfig, error) {
return dns.OSConfig{}, dns.ErrGetBaseConfigNotSupported
if r.GetBaseConfigFunc == nil {
return dns.OSConfig{}, dns.ErrGetBaseConfigNotSupported
}
return r.GetBaseConfigFunc()
}
func (r *CallbackRouter) Close() error {

2
wgengine/userspace.go
View File

@ -1199,7 +1199,7 @@ func (e *userspaceEngine) linkChange(changed bool, cur *interfaces.State) {
// suspend/resume or whenever NetworkManager is started, it
// nukes all systemd-resolved configs. So reapply our DNS
// config on major link change.
if runtime.GOOS == "linux" && changed {
if (runtime.GOOS == "linux" || runtime.GOOS == "android") && changed {
e.wgLock.Lock()
dnsCfg := e.lastDNSConfig
e.wgLock.Unlock()