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0112da6070
Updates tailscale/tailscale#177 It appears that the OSS distribution of `tailscaled` is currently unable to get the current system base DNS configuration, as GetBaseConfig() in manager_darwin.go is unimplemented. This PR adds a basic implementation that reads the current values in `/etc/resolv.conf`, to at least unblock DNS resolution via Quad100 if `--accept-dns` is enabled. Signed-off-by: Andrea Gottardo <andrea@gottardo.me>
157 lines
4.5 KiB
Go
157 lines
4.5 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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"os"
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"go4.org/mem"
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"tailscale.com/control/controlknobs"
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"tailscale.com/health"
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"tailscale.com/net/dns/resolvconffile"
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"tailscale.com/net/tsaddr"
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"tailscale.com/types/logger"
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"tailscale.com/util/mak"
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)
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// NewOSConfigurator creates a new OS configurator.
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//
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// The health tracker and the knobs may be nil and are ignored on this platform.
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func NewOSConfigurator(logf logger.Logf, _ *health.Tracker, _ *controlknobs.Knobs, ifName string) (OSConfigurator, error) {
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return &darwinConfigurator{logf: logf, ifName: ifName}, nil
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}
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// darwinConfigurator is the tailscaled-on-macOS DNS OS configurator that
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// maintains the Split DNS nameserver entries pointing MagicDNS DNS suffixes
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// to 100.100.100.100 using the macOS /etc/resolver/$SUFFIX files.
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type darwinConfigurator struct {
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logf logger.Logf
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ifName string
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}
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func (c *darwinConfigurator) Close() error {
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c.removeResolverFiles(func(domain string) bool { return true })
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return nil
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}
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func (c *darwinConfigurator) SupportsSplitDNS() bool {
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return true
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}
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func (c *darwinConfigurator) SetDNS(cfg OSConfig) error {
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var buf bytes.Buffer
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buf.WriteString(macResolverFileHeader)
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for _, ip := range cfg.Nameservers {
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buf.WriteString("nameserver ")
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buf.WriteString(ip.String())
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buf.WriteString("\n")
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}
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if err := os.MkdirAll("/etc/resolver", 0755); err != nil {
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return err
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}
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var keep map[string]bool
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// Add a dummy file to /etc/resolver with a "search ..." directive if we have
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// search suffixes to add.
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if len(cfg.SearchDomains) > 0 {
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const searchFile = "search.tailscale" // fake DNS suffix+TLD to put our search
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mak.Set(&keep, searchFile, true)
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var sbuf bytes.Buffer
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sbuf.WriteString(macResolverFileHeader)
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sbuf.WriteString("search")
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for _, d := range cfg.SearchDomains {
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sbuf.WriteString(" ")
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sbuf.WriteString(string(d.WithoutTrailingDot()))
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}
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sbuf.WriteString("\n")
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if err := os.WriteFile("/etc/resolver/"+searchFile, sbuf.Bytes(), 0644); err != nil {
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return err
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}
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}
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for _, d := range cfg.MatchDomains {
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fileBase := string(d.WithoutTrailingDot())
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mak.Set(&keep, fileBase, true)
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fullPath := "/etc/resolver/" + fileBase
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if err := os.WriteFile(fullPath, buf.Bytes(), 0644); err != nil {
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return err
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}
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}
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return c.removeResolverFiles(func(domain string) bool { return !keep[domain] })
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}
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// GetBaseConfig returns the current OS DNS configuration, extracting it from /etc/resolv.conf.
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// We should really be using the SystemConfiguration framework to get this information, as this
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// is not a stable public API, and is provided mostly as a compatibility effort with Unix
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// tools. Apple might break this in the future. But honestly, parsing the output of `scutil --dns`
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// is *even more* likely to break in the future.
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func (c *darwinConfigurator) GetBaseConfig() (OSConfig, error) {
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cfg := OSConfig{}
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resolvConf, err := resolvconffile.ParseFile("/etc/resolv.conf")
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if err != nil {
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c.logf("failed to parse /etc/resolv.conf: %v", err)
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return cfg, ErrGetBaseConfigNotSupported
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}
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for _, ns := range resolvConf.Nameservers {
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if ns == tsaddr.TailscaleServiceIP() || ns == tsaddr.TailscaleServiceIPv6() {
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// If we find Quad100 in /etc/resolv.conf, we should ignore it
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c.logf("ignoring 100.100.100.100 resolver IP found in /etc/resolv.conf")
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continue
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}
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cfg.Nameservers = append(cfg.Nameservers, ns)
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}
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cfg.SearchDomains = resolvConf.SearchDomains
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if len(cfg.Nameservers) == 0 {
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// Log a warning in case we couldn't find any nameservers in /etc/resolv.conf.
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c.logf("no nameservers found in /etc/resolv.conf, DNS resolution might fail")
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}
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return cfg, nil
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}
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const macResolverFileHeader = "# Added by tailscaled\n"
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// removeResolverFiles deletes all files in /etc/resolver for which the shouldDelete
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// func returns true.
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func (c *darwinConfigurator) removeResolverFiles(shouldDelete func(domain string) bool) error {
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dents, err := os.ReadDir("/etc/resolver")
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if os.IsNotExist(err) {
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return nil
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}
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if err != nil {
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return err
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}
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for _, de := range dents {
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if !de.Type().IsRegular() {
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continue
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}
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name := de.Name()
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if !shouldDelete(name) {
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continue
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}
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fullPath := "/etc/resolver/" + name
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contents, err := os.ReadFile(fullPath)
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if err != nil {
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if os.IsNotExist(err) { // race?
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continue
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}
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return err
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}
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if !mem.HasPrefix(mem.B(contents), mem.S(macResolverFileHeader)) {
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continue
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}
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if err := os.Remove(fullPath); err != nil {
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return err
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}
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}
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return nil
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}
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