mirror of
https://github.com/tailscale/tailscale.git
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123 lines
2.8 KiB
Go
123 lines
2.8 KiB
Go
// Copyright (c) 2020 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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//go:build linux
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// +build linux
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package router
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import (
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"errors"
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"fmt"
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"os"
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"os/exec"
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"strconv"
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"strings"
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"syscall"
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"golang.org/x/sys/unix"
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)
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// commandRunner abstracts helpers to run OS commands. It exists
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// purely to swap out osCommandRunner (below) with a fake runner in
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// tests.
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type commandRunner interface {
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run(...string) error
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output(...string) ([]byte, error)
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}
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type osCommandRunner struct {
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// ambientCapNetAdmin determines whether commands are executed with
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// CAP_NET_ADMIN.
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// CAP_NET_ADMIN is required when running as non-root and executing cmds
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// like `ip rule`. Even if our process has the capability, we need to
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// explicitly grant it to the new process.
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// We specifically need this for Synology DSM7 where tailscaled no longer
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// runs as root.
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ambientCapNetAdmin bool
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}
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// errCode extracts and returns the process exit code from err, or
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// zero if err is nil.
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func errCode(err error) int {
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if err == nil {
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return 0
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}
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var e *exec.ExitError
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if ok := errors.As(err, &e); ok {
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return e.ExitCode()
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}
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s := err.Error()
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if strings.HasPrefix(s, "exitcode:") {
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code, err := strconv.Atoi(s[9:])
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if err == nil {
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return code
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}
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}
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return -42
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}
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func (o osCommandRunner) run(args ...string) error {
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_, err := o.output(args...)
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return err
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}
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func (o osCommandRunner) output(args ...string) ([]byte, error) {
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if len(args) == 0 {
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return nil, errors.New("cmd: no argv[0]")
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}
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cmd := exec.Command(args[0], args[1:]...)
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cmd.Env = append(os.Environ(), "LC_ALL=C")
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if o.ambientCapNetAdmin {
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cmd.SysProcAttr = &syscall.SysProcAttr{
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AmbientCaps: []uintptr{unix.CAP_NET_ADMIN},
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}
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}
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out, err := cmd.CombinedOutput()
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if err != nil {
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return nil, fmt.Errorf("running %q failed: %w\n%s", strings.Join(args, " "), err, out)
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}
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return out, nil
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}
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type runGroup struct {
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OkCode []int // error codes that are acceptable, other than 0, if any
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Runner commandRunner // the runner that actually runs our commands
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ErrAcc error // first error encountered, if any
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}
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func newRunGroup(okCode []int, runner commandRunner) *runGroup {
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return &runGroup{
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OkCode: okCode,
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Runner: runner,
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}
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}
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func (rg *runGroup) okCode(err error) bool {
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got := errCode(err)
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for _, want := range rg.OkCode {
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if got == want {
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return true
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}
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}
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return false
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}
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func (rg *runGroup) Output(args ...string) []byte {
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b, err := rg.Runner.output(args...)
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if rg.ErrAcc == nil && err != nil && !rg.okCode(err) {
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rg.ErrAcc = err
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}
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return b
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}
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func (rg *runGroup) Run(args ...string) {
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err := rg.Runner.run(args...)
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if rg.ErrAcc == nil && err != nil && !rg.okCode(err) {
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rg.ErrAcc = err
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}
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}
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