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tailscale/net/dns/direct_linux.go

115 lines
2.5 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package dns
import (
"bytes"
"context"
"github.com/illarion/gonotify"
"tailscale.com/health"
)
func (m *directManager) runFileWatcher() {
in, err := gonotify.NewInotify()
if err != nil {
// Oh well, we tried. This is all best effort for now, to
// surface warnings to users.
m.logf("dns: inotify new: %v", err)
return
}
ctx, cancel := context.WithCancel(m.ctx)
defer cancel()
go m.closeInotifyOnDone(ctx, in)
const events = gonotify.IN_ATTRIB |
gonotify.IN_CLOSE_WRITE |
gonotify.IN_CREATE |
gonotify.IN_DELETE |
gonotify.IN_MODIFY |
gonotify.IN_MOVE
if err := in.AddWatch("/etc/", events); err != nil {
m.logf("dns: inotify addwatch: %v", err)
return
}
for {
events, err := in.Read()
if ctx.Err() != nil {
return
}
if err != nil {
m.logf("dns: inotify read: %v", err)
return
}
var match bool
for _, ev := range events {
if ev.Name == resolvConf {
match = true
break
}
}
if !match {
continue
}
m.checkForFileTrample()
}
}
var resolvTrampleWarnable = health.Register(&health.Warnable{
Code: "resolv-conf-overwritten",
Severity: health.SeverityMedium,
Title: "Linux DNS configuration issue",
Text: health.StaticMessage("Linux DNS config not ideal. /etc/resolv.conf overwritten. See https://tailscale.com/s/dns-fight"),
})
// checkForFileTrample checks whether /etc/resolv.conf has been trampled
// by another program on the system. (e.g. a DHCP client)
func (m *directManager) checkForFileTrample() {
m.mu.Lock()
want := m.wantResolvConf
lastWarn := m.lastWarnContents
m.mu.Unlock()
if want == nil {
return
}
cur, err := m.fs.ReadFile(resolvConf)
if err != nil {
m.logf("trample: read error: %v", err)
return
}
if bytes.Equal(cur, want) {
m.health.SetHealthy(resolvTrampleWarnable)
if lastWarn != nil {
m.mu.Lock()
m.lastWarnContents = nil
m.mu.Unlock()
m.logf("trample: resolv.conf again matches expected content")
}
return
}
if bytes.Equal(cur, lastWarn) {
// We already logged about this, so not worth doing it again.
return
}
m.mu.Lock()
m.lastWarnContents = cur
m.mu.Unlock()
show := cur
if len(show) > 1024 {
show = show[:1024]
}
m.logf("trample: resolv.conf changed from what we expected. did some other program interfere? current contents: %q", show)
m.health.SetUnhealthy(resolvTrampleWarnable, nil)
}
func (m *directManager) closeInotifyOnDone(ctx context.Context, in *gonotify.Inotify) {
<-ctx.Done()
in.Close()
}