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