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ssh/tailssh: move some user-related code into new user.go

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The previous commit 58ab66e added ssh/tailssh/user.go as part of
working on #4945. So move some more user-related code over to it.

Updates #cleanup

Change-Id: I24de66df25ffb8f867e1a0a540d410f9ef16d7b0
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
pull/8012/head
Brad Fitzpatrick 1 year ago committed by Brad Fitzpatrick
parent 58ab66ec51
commit a743b66f9d
2 changed files with 113 additions and 109 deletions
Show Stats Download Patch File Download Diff File

107
ssh/tailssh/incubator.go
Unescape Escape View File

@ -20,7 +20,6 @@ import (
"log/syslog"
"os"
"os/exec"
"os/user"
"path/filepath"
"runtime"
"sort"
@ -31,16 +30,12 @@ import (
"github.com/creack/pty"
"github.com/pkg/sftp"
"github.com/u-root/u-root/pkg/termios"
"go4.org/mem"
gossh "golang.org/x/crypto/ssh"
"golang.org/x/exp/slices"
"golang.org/x/sys/unix"
"tailscale.com/cmd/tailscaled/childproc"
"tailscale.com/envknob"
"tailscale.com/hostinfo"
"tailscale.com/tempfork/gliderlabs/ssh"
"tailscale.com/types/logger"
"tailscale.com/util/lineread"
"tailscale.com/version/distro"
)
@ -83,7 +78,7 @@ func (ss *sshSession) newIncubatorCommand() (cmd *exec.Cmd) {
case "sftp":
isSFTP = true
case "":
name = loginShell(ss.conn.localUser)
name = ss.conn.localUser.LoginShell()
if rawCmd := ss.RawCommand(); rawCmd != "" {
args = append(args, "-c", rawCmd)
} else {
@ -688,113 +683,15 @@ func (ss *sshSession) startWithStdPipes() (err error) {
return nil
}
func loginShell(u *userMeta) string {
if u.LoginShell != "" {
// This field should be populated on Linux, at least, because
// func userLookup on Linux uses "getent" to look up the user
// and that populates it.
return u.LoginShell
}
switch runtime.GOOS {
case "darwin":
// Note: /Users/username is key, and not the same as u.HomeDir.
out, _ := exec.Command("dscl", ".", "-read", filepath.Join("/Users", u.Username), "UserShell").Output()
// out is "UserShell: /bin/bash"
s, ok := strings.CutPrefix(string(out), "UserShell: ")
if ok {
return strings.TrimSpace(s)
}
}
if e := os.Getenv("SHELL"); e != "" {
return e
}
return "/bin/sh"
}
func envForUser(u *userMeta) []string {
return []string{
fmt.Sprintf("SHELL=" + loginShell(u)),
fmt.Sprintf("SHELL=" + u.LoginShell()),
fmt.Sprintf("USER=" + u.Username),
fmt.Sprintf("HOME=" + u.HomeDir),
fmt.Sprintf("PATH=" + defaultPathForUser(&u.User)),
}
}
// defaultPathTmpl specifies the default PATH template to use for new sessions.
//
// If empty, a default value is used based on the OS & distro to match OpenSSH's
// usually-hardcoded behavior. (see
// https://github.com/tailscale/tailscale/issues/5285 for background).
//
// The template may contain @{HOME} or @{PAM_USER} which expand to the user's
// home directory and username, respectively. (PAM is not used, despite the
// name)
var defaultPathTmpl = envknob.RegisterString("TAILSCALE_SSH_DEFAULT_PATH")
func defaultPathForUser(u *user.User) string {
if s := defaultPathTmpl(); s != "" {
return expandDefaultPathTmpl(s, u)
}
isRoot := u.Uid == "0"
switch distro.Get() {
case distro.Debian:
hi := hostinfo.New()
if hi.Distro == "ubuntu" {
// distro.Get's Debian includes Ubuntu. But see if it's actually Ubuntu.
// Ubuntu doesn't empirically seem to distinguish between root and non-root for the default.
// And it includes /snap/bin.
return "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin"
}
if isRoot {
return "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
}
return "/usr/local/bin:/usr/bin:/bin:/usr/bn/games"
case distro.NixOS:
return defaultPathForUserOnNixOS(u)
}
if isRoot {
return "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
}
return "/usr/local/bin:/usr/bin:/bin"
}
func defaultPathForUserOnNixOS(u *user.User) string {
var path string
lineread.File("/etc/pam/environment", func(lineb []byte) error {
if v := pathFromPAMEnvLine(lineb, u); v != "" {
path = v
return io.EOF // stop iteration
}
return nil
})
return path
}
func pathFromPAMEnvLine(line []byte, u *user.User) (path string) {
if !mem.HasPrefix(mem.B(line), mem.S("PATH")) {
return ""
}
rest := strings.TrimSpace(strings.TrimPrefix(string(line), "PATH"))
if quoted, ok := strings.CutPrefix(rest, "DEFAULT="); ok {
if path, err := strconv.Unquote(quoted); err == nil {
return expandDefaultPathTmpl(path, u)
}
}
return ""
}
func expandDefaultPathTmpl(t string, u *user.User) string {
p := strings.NewReplacer(
"@{HOME}", u.HomeDir,
"@{PAM_USER}", u.Username,
).Replace(t)
if strings.Contains(p, "@{") {
// If there are unknown expansions, conservatively fail closed.
return ""
}
return p
}
// updateStringInSlice mutates ss to change the first occurrence of a
// to b.
func updateStringInSlice(ss []string, a, b string) {

115
ssh/tailssh/user.go
Unescape Escape View File

@ -8,14 +8,22 @@ package tailssh
import (
"context"
"errors"
"io"
"log"
"os"
"os/exec"
"os/user"
"path/filepath"
"runtime"
"strconv"
"strings"
"time"
"unicode/utf8"
"go4.org/mem"
"tailscale.com/envknob"
"tailscale.com/hostinfo"
"tailscale.com/util/lineread"
"tailscale.com/version/distro"
)
@ -23,8 +31,9 @@ import (
type userMeta struct {
user.User
// LoginShell is the user's login shell.
LoginShell string
// loginShellCached is the user's login shell, if known
// at the time of userLookup.
loginShellCached string
}
// GroupIds returns the list of group IDs that the user is a member of.
@ -50,7 +59,7 @@ func userLookup(uid string) (*userMeta, error) {
if distro.Get() == distro.Gokrazy {
um, err := userLookupStd(uid)
if err == nil {
um.LoginShell = "/tmp/serial-busybox/ash"
um.loginShellCached = "/tmp/serial-busybox/ash"
}
return um, err
}
@ -102,7 +111,7 @@ func userLookupGetent(uid string) (*userMeta, error) {
Name: f[4],
HomeDir: f[5],
},
LoginShell: f[6],
loginShellCached: f[6],
}
return um, nil
}
@ -114,3 +123,101 @@ func userLookupStd(uid string) (*userMeta, error) {
}
return &userMeta{User: *u}, nil
}
func (u *userMeta) LoginShell() string {
if u.loginShellCached != "" {
// This field should be populated on Linux, at least, because
// func userLookup on Linux uses "getent" to look up the user
// and that populates it.
return u.loginShellCached
}
switch runtime.GOOS {
case "darwin":
// Note: /Users/username is key, and not the same as u.HomeDir.
out, _ := exec.Command("dscl", ".", "-read", filepath.Join("/Users", u.Username), "UserShell").Output()
// out is "UserShell: /bin/bash"
s, ok := strings.CutPrefix(string(out), "UserShell: ")
if ok {
return strings.TrimSpace(s)
}
}
if e := os.Getenv("SHELL"); e != "" {
return e
}
return "/bin/sh"
}
// defaultPathTmpl specifies the default PATH template to use for new sessions.
//
// If empty, a default value is used based on the OS & distro to match OpenSSH's
// usually-hardcoded behavior. (see
// https://github.com/tailscale/tailscale/issues/5285 for background).
//
// The template may contain @{HOME} or @{PAM_USER} which expand to the user's
// home directory and username, respectively. (PAM is not used, despite the
// name)
var defaultPathTmpl = envknob.RegisterString("TAILSCALE_SSH_DEFAULT_PATH")
func defaultPathForUser(u *user.User) string {
if s := defaultPathTmpl(); s != "" {
return expandDefaultPathTmpl(s, u)
}
isRoot := u.Uid == "0"
switch distro.Get() {
case distro.Debian:
hi := hostinfo.New()
if hi.Distro == "ubuntu" {
// distro.Get's Debian includes Ubuntu. But see if it's actually Ubuntu.
// Ubuntu doesn't empirically seem to distinguish between root and non-root for the default.
// And it includes /snap/bin.
return "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin"
}
if isRoot {
return "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
}
return "/usr/local/bin:/usr/bin:/bin:/usr/bn/games"
case distro.NixOS:
return defaultPathForUserOnNixOS(u)
}
if isRoot {
return "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
}
return "/usr/local/bin:/usr/bin:/bin"
}
func defaultPathForUserOnNixOS(u *user.User) string {
var path string
lineread.File("/etc/pam/environment", func(lineb []byte) error {
if v := pathFromPAMEnvLine(lineb, u); v != "" {
path = v
return io.EOF // stop iteration
}
return nil
})
return path
}
func pathFromPAMEnvLine(line []byte, u *user.User) (path string) {
if !mem.HasPrefix(mem.B(line), mem.S("PATH")) {
return ""
}
rest := strings.TrimSpace(strings.TrimPrefix(string(line), "PATH"))
if quoted, ok := strings.CutPrefix(rest, "DEFAULT="); ok {
if path, err := strconv.Unquote(quoted); err == nil {
return expandDefaultPathTmpl(path, u)
}
}
return ""
}
func expandDefaultPathTmpl(t string, u *user.User) string {
p := strings.NewReplacer(
"@{HOME}", u.HomeDir,
"@{PAM_USER}", u.Username,
).Replace(t)
if strings.Contains(p, "@{") {
// If there are unknown expansions, conservatively fail closed.
return ""
}
return p
}

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