mirror of
https://github.com/tailscale/tailscale.git
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95 lines
2.6 KiB
Go
95 lines
2.6 KiB
Go
// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build linux freebsd openbsd
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package dns
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import (
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"bytes"
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"fmt"
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"os/exec"
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"strings"
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)
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// openresolvManager manages DNS configuration using the openresolv
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// implementation of the `resolvconf` program.
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type openresolvManager struct{}
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func newOpenresolvManager() (openresolvManager, error) {
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return openresolvManager{}, nil
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}
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func (m openresolvManager) deleteTailscaleConfig() error {
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cmd := exec.Command("resolvconf", "-f", "-d", "tailscale")
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out, err := cmd.CombinedOutput()
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if err != nil {
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return fmt.Errorf("running %s: %s", cmd, out)
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}
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return nil
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}
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func (m openresolvManager) SetDNS(config OSConfig) error {
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if config.IsZero() {
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return m.deleteTailscaleConfig()
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}
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var stdin bytes.Buffer
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writeResolvConf(&stdin, config.Nameservers, config.SearchDomains)
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cmd := exec.Command("resolvconf", "-m", "0", "-x", "-a", "tailscale")
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cmd.Stdin = &stdin
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out, err := cmd.CombinedOutput()
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if err != nil {
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return fmt.Errorf("running %s: %s", cmd, out)
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}
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return nil
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}
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func (m openresolvManager) SupportsSplitDNS() bool {
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return false
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}
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func (m openresolvManager) GetBaseConfig() (OSConfig, error) {
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// List the names of all config snippets openresolv is aware
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// of. Snippets get listed in priority order (most to least),
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// which we'll exploit later.
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bs, err := exec.Command("resolvconf", "-i").CombinedOutput()
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if err != nil {
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return OSConfig{}, err
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}
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// Remove the "tailscale" snippet from the list.
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args := []string{"-l"}
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for _, f := range strings.Split(strings.TrimSpace(string(bs)), " ") {
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if f == "tailscale" {
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continue
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}
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args = append(args, f)
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}
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// List all resolvconf snippets except our own, and parse that as
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// a resolv.conf. This effectively generates a blended config of
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// "everyone except tailscale", which is what would be in use if
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// tailscale hadn't set exclusive mode.
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//
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// Note that this is not _entirely_ true. To be perfectly correct,
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// we should be looking for other interfaces marked exclusive that
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// predated tailscale, and stick to only those. However, in
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// practice, openresolv uses are generally quite limited, and boil
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// down to 1-2 DHCP leases, for which the correct outcome is a
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// blended config like the one we produce here.
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var buf bytes.Buffer
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cmd := exec.Command("resolvconf", args...)
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cmd.Stdout = &buf
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if err := cmd.Run(); err != nil {
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return OSConfig{}, err
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}
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return readResolv(&buf)
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}
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func (m openresolvManager) Close() error {
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return m.deleteTailscaleConfig()
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}
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