wgengine/router: dns: unify on *BSD, multimode on Linux, Magic DNS (#536)

Signed-off-by: Dmytro Shynkevych <dmytro@tailscale.com>

wgengine/router/router_openbsd.go

@@ -5,20 +5,14 @@
 package router
 
 import (
-	"bytes"
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"log"
-	"os"
 	"os/exec"
-	"path/filepath"
-	"strings"
 
 	"github.com/tailscale/wireguard-go/device"
 	"github.com/tailscale/wireguard-go/tun"
 	"inet.af/netaddr"
-	"tailscale.com/atomicfile"
 	"tailscale.com/types/logger"
 )
 
@@ -31,6 +25,8 @@ type openbsdRouter struct {
 	tunname string
 	local   netaddr.IPPrefix
 	routes  map[netaddr.IPPrefix]struct{}
+
+	dnsConfig DNSConfig
 }
 
 func newUserspaceRouter(logf logger.Logf, _ *device.Device, tundev tun.Device) (Router, error) {
@@ -159,112 +155,28 @@ func (r *openbsdRouter) Set(cfg *Config) error {
 	r.local = localAddr
 	r.routes = newRoutes
 
-	if err := r.replaceResolvConf(cfg.DNS, cfg.DNSDomains); err != nil {
-		errq = fmt.Errorf("replacing resolv.conf failed: %v", err)
+	if !r.dnsConfig.EquivalentTo(cfg.DNSConfig) {
+		if err := dnsDirectUp(cfg.DNSConfig); err != nil {
+			errq = fmt.Errorf("dns up: direct: %v", err)
+		} else {
+			r.dnsConfig = cfg.DNSConfig
+		}
 	}
 
 	return errq
 }
 
 func (r *openbsdRouter) Close() error {
-	out, err := cmd("ifconfig", r.tunname, "down").CombinedOutput()
+	cleanup(r.logf, r.tunname)
+	return nil
+}
+
+func cleanup(logf logger.Logf, interfaceName string) {
+	if err := dnsDirectDown(); err != nil {
+		logf("dns down: direct: %v", err)
+	}
+	out, err := cmd("ifconfig", interfaceName, "down").CombinedOutput()
 	if err != nil {
-		r.logf("running ifconfig failed: %v\n%s", err, out)
+		logf("ifconfig down: %v\n%s", err, out)
 	}
-
-	if err := r.restoreResolvConf(); err != nil {
-		r.logf("failed to restore system resolv.conf: %v", err)
-	}
-
-	return nil
-}
-
-const (
-	tsConf     = "/etc/resolv.tailscale.conf"
-	backupConf = "/etc/resolv.pre-tailscale-backup.conf"
-	resolvConf = "/etc/resolv.conf"
-)
-
-func (r *openbsdRouter) replaceResolvConf(servers []netaddr.IP, domains []string) error {
-	if len(servers) == 0 {
-		return r.restoreResolvConf()
-	}
-
-	// Write the tsConf file.
-	buf := new(bytes.Buffer)
-	fmt.Fprintf(buf, "# resolv.conf(5) file generated by tailscale\n")
-	fmt.Fprintf(buf, "# DO NOT EDIT THIS FILE BY HAND -- CHANGES WILL BE OVERWRITTEN\n\n")
-	for _, ns := range servers {
-		fmt.Fprintf(buf, "nameserver %s\n", ns)
-	}
-	if len(domains) > 0 {
-		fmt.Fprintf(buf, "search "+strings.Join(domains, " ")+"\n")
-	}
-	tf, err := ioutil.TempFile(filepath.Dir(tsConf), filepath.Base(tsConf)+".*")
-	if err != nil {
-		return err
-	}
-	tempName := tf.Name()
-	tf.Close()
-
-	if err := atomicfile.WriteFile(tempName, buf.Bytes(), 0644); err != nil {
-		return err
-	}
-	if err := os.Rename(tempName, tsConf); err != nil {
-		return err
-	}
-
-	if linkPath, err := os.Readlink(resolvConf); err != nil {
-		// Remove any old backup that may exist.
-		os.Remove(backupConf)
-
-		// Backup the existing /etc/resolv.conf file.
-		contents, err := ioutil.ReadFile(resolvConf)
-		if os.IsNotExist(err) {
-			// No existing /etc/resolv.conf file to backup.
-			// Nothing to do.
-			return nil
-		} else if err != nil {
-			return err
-		}
-		if err := atomicfile.WriteFile(backupConf, contents, 0644); err != nil {
-			return err
-		}
-	} else if linkPath != tsConf {
-		// Backup the existing symlink.
-		os.Remove(backupConf)
-		if err := os.Symlink(linkPath, backupConf); err != nil {
-			return err
-		}
-	} else {
-		// Nothing to do, resolvConf already points to tsConf.
-		return nil
-	}
-
-	os.Remove(resolvConf)
-	if err := os.Symlink(tsConf, resolvConf); err != nil {
-		return nil
-	}
-
-	return nil
-}
-
-func (r *openbsdRouter) restoreResolvConf() error {
-	if _, err := os.Stat(backupConf); err != nil {
-		if os.IsNotExist(err) {
-			return nil // No backup resolv.conf to restore.
-		}
-		return err
-	}
-	if ln, err := os.Readlink(resolvConf); err != nil {
-		return err
-	} else if ln != tsConf {
-		return fmt.Errorf("resolv.conf is not a symlink to %s", tsConf)
-	}
-	if err := os.Rename(backupConf, resolvConf); err != nil {
-		return err
-	}
-	os.Remove(tsConf) // Best effort removal.
-
-	return nil
 }