93 lines
2.5 KiB
Go
93 lines
2.5 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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// Package tun creates a tuntap device, working around OS-specific
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// quirks if necessary.
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package tstun
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import (
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"errors"
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"os"
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"runtime"
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"strconv"
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"strings"
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"time"
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"golang.zx2c4.com/wireguard/tun"
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"tailscale.com/types/logger"
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)
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// tunMTU is the MTU we set on tailscale's TUN interface. wireguard-go
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// defaults to 1420 bytes, which only works if the "outer" MTU is 1500
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// bytes. This breaks on DSL connections (typically 1492 MTU) and on
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// GCE (1460 MTU?!).
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//
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// 1280 is the smallest MTU allowed for IPv6, which is a sensible
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// "probably works everywhere" setting until we develop proper PMTU
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// discovery.
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var tunMTU = 1280
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func init() {
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if mtu, _ := strconv.Atoi(os.Getenv("TS_DEBUG_MTU")); mtu != 0 {
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tunMTU = mtu
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}
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}
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// createTAP is non-nil on Linux.
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var createTAP func(tapName, bridgeName string) (tun.Device, error)
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// New returns a tun.Device for the requested device name, along with
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// the OS-dependent name that was allocated to the device.
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func New(logf logger.Logf, tunName string) (tun.Device, string, error) {
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var dev tun.Device
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var err error
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if strings.HasPrefix(tunName, "tap:") {
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if runtime.GOOS != "linux" {
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return nil, "", errors.New("tap only works on Linux")
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}
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f := strings.Split(tunName, ":")
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var tapName, bridgeName string
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switch len(f) {
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case 2:
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tapName = f[1]
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case 3:
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tapName, bridgeName = f[1], f[2]
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default:
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return nil, "", errors.New("bogus tap argument")
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}
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dev, err = createTAP(tapName, bridgeName)
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} else {
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dev, err = tun.CreateTUN(tunName, tunMTU)
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}
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if err != nil {
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return nil, "", err
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}
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if err := waitInterfaceUp(dev, 90*time.Second, logf); err != nil {
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dev.Close()
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return nil, "", err
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}
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name, err := interfaceName(dev)
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if err != nil {
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dev.Close()
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return nil, "", err
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}
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return dev, name, nil
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}
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// tunDiagnoseFailure, if non-nil, does OS-specific diagnostics of why
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// TUN failed to work.
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var tunDiagnoseFailure func(tunName string, logf logger.Logf)
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// Diagnose tries to explain a tuntap device creation failure.
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// It pokes around the system and logs some diagnostic info that might
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// help debug why tun creation failed. Because device creation has
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// already failed and the program's about to end, log a lot.
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func Diagnose(logf logger.Logf, tunName string) {
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if tunDiagnoseFailure != nil {
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tunDiagnoseFailure(tunName, logf)
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} else {
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logf("no TUN failure diagnostics for OS %q", runtime.GOOS)
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}
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}
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