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net/dns: retrample resolve.conf when another process has trampled it (#18069)

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When using the resolve.conf file for setting DNS, it is possible that
some other services will trample the file and overwrite our set DNS
server. Experiments has shown this to be a racy error depending on how
quickly processes start.

Make an attempt to trample back the file a limited number of times if
the file is changed.

Updates #16635

Signed-off-by: Claus Lensbøl <claus@tailscale.com>
This commit is contained in:
Claus Lensbøl
2025-12-09 14:55:26 -05:00
committed by GitHub
parent a9b37c510c
commit 1dfdee8521
17 changed files with 261 additions and 45 deletions
Download Patch File Download Diff File Expand all files Collapse all files
net/dns/manager_test.go
+40 -2
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@@ -6,9 +6,11 @@ package dns
import (
"errors"
"net/netip"
"reflect"
"runtime"
"strings"
"testing"
"testing/synctest"
"github.com/google/go-cmp/cmp"
"github.com/google/go-cmp/cmp/cmpopts"
@@ -936,7 +938,7 @@ func TestManager(t *testing.T) {
bus := eventbustest.NewBus(t)
dialer := tsdial.NewDialer(netmon.NewStatic())
dialer.SetBus(bus)
m := NewManager(t.Logf, &f, health.NewTracker(bus), dialer, nil, knobs, goos)
m := NewManager(t.Logf, &f, health.NewTracker(bus), dialer, nil, knobs, goos, bus)
m.resolver.TestOnlySetHook(f.SetResolver)
if err := m.Set(test.in); err != nil {
@@ -1045,7 +1047,7 @@ func TestConfigRecompilation(t *testing.T) {
bus := eventbustest.NewBus(t)
dialer := tsdial.NewDialer(netmon.NewStatic())
dialer.SetBus(bus)
m := NewManager(t.Logf, f, health.NewTracker(bus), dialer, nil, nil, "darwin")
m := NewManager(t.Logf, f, health.NewTracker(bus), dialer, nil, nil, "darwin", bus)
var managerConfig *resolver.Config
m.resolver.TestOnlySetHook(func(cfg resolver.Config) {
@@ -1078,3 +1080,39 @@ func TestConfigRecompilation(t *testing.T) {
t.Fatalf("Want non nil managerConfig. Got nil")
}
}
func TestTrampleRetrample(t *testing.T) {
synctest.Test(t, func(t *testing.T) {
f := &fakeOSConfigurator{}
f.BaseConfig = OSConfig{
Nameservers: mustIPs("1.1.1.1"),
}
config := Config{
Routes: upstreams("ts.net", "69.4.2.0", "foo.ts.net", ""),
SearchDomains: fqdns("foo.ts.net"),
}
bus := eventbustest.NewBus(t)
dialer := tsdial.NewDialer(netmon.NewStatic())
dialer.SetBus(bus)
m := NewManager(t.Logf, f, health.NewTracker(bus), dialer, nil, nil, "linux", bus)
// Initial set should error out and store the config
if err := m.Set(config); err != nil {
t.Fatalf("Want nil error. Got non-nil")
}
// Set no config
f.OSConfig = OSConfig{}
inj := eventbustest.NewInjector(t, bus)
eventbustest.Inject(inj, TrampleDNS{})
synctest.Wait()
t.Logf("OSConfig: %+v", f.OSConfig)
if reflect.DeepEqual(f.OSConfig, OSConfig{}) {
t.Errorf("Expected config to be set, got empty config")
}
})
}