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net/dns: add GetBaseConfig to CallbackRouter. 

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>
pull/3544/head
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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
ipn/ipnlocal/dnsconfig_test.go
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@ -232,32 +232,11 @@ func TestDNSConfigForNetmap(t *testing.T) {
}, },
}, },
{ {
name: "android_does_need_fallbacks", // Prior to fixing https://github.com/tailscale/tailscale/issues/2116,
os: "android", // Android had cases where it needed FallbackResolvers. This was the
nm: &netmap.NetworkMap{ // negative test for the case where Override-local-DNS was set, so the
DNS: tailcfg.DNSConfig{ // fallback resolvers did not need to be used. This test is still valid
FallbackResolvers: []dnstype.Resolver{ // so we keep it, but the fallback test has been removed.
{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"}},
},
},
},
{
name: "android_does_NOT_need_fallbacks", name: "android_does_NOT_need_fallbacks",
os: "android", os: "android",
nm: &netmap.NetworkMap{ nm: &netmap.NetworkMap{

3
ipn/ipnlocal/local.go
View File

@ -2091,9 +2091,6 @@ func dnsConfigForNetmap(nm *netmap.NetworkMap, prefs *ipn.Prefs, logf logger.Log
addDefault(nm.DNS.FallbackResolvers) addDefault(nm.DNS.FallbackResolvers)
case len(dcfg.Routes) == 0: case len(dcfg.Routes) == 0:
// No settings requiring split DNS, no problem. // 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 return dcfg

10
wgengine/router/callback.go
View File

@ -18,6 +18,13 @@ type CallbackRouter struct {
SetBoth func(rcfg *Config, dcfg *dns.OSConfig) error SetBoth func(rcfg *Config, dcfg *dns.OSConfig) error
SplitDNS bool 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 mu sync.Mutex // protects all the following
rcfg *Config // last applied router config rcfg *Config // last applied router config
dcfg *dns.OSConfig // last applied DNS config dcfg *dns.OSConfig // last applied DNS config
@ -50,8 +57,11 @@ func (r *CallbackRouter) SupportsSplitDNS() bool {
} }
func (r *CallbackRouter) GetBaseConfig() (dns.OSConfig, error) { func (r *CallbackRouter) GetBaseConfig() (dns.OSConfig, error) {
if r.GetBaseConfigFunc == nil {
return dns.OSConfig{}, dns.ErrGetBaseConfigNotSupported return dns.OSConfig{}, dns.ErrGetBaseConfigNotSupported
} }
return r.GetBaseConfigFunc()
}
func (r *CallbackRouter) Close() error { func (r *CallbackRouter) Close() error {
return r.SetBoth(nil, nil) // TODO: check if makes sense return r.SetBoth(nil, nil) // TODO: check if makes sense

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 // suspend/resume or whenever NetworkManager is started, it
// nukes all systemd-resolved configs. So reapply our DNS // nukes all systemd-resolved configs. So reapply our DNS
// config on major link change. // config on major link change.
if runtime.GOOS == "linux" && changed { if (runtime.GOOS == "linux" || runtime.GOOS == "android") && changed {
e.wgLock.Lock() e.wgLock.Lock()
dnsCfg := e.lastDNSConfig dnsCfg := e.lastDNSConfig
e.wgLock.Unlock() e.wgLock.Unlock()