tailscale/ipn/ipnauth/ipnauth.go

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// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package ipnauth controls access to the LocalAPI.
package ipnauth
import (
"fmt"
"net"
"net/netip"
"os"
"os/user"
"runtime"
"strconv"
"inet.af/peercred"
"tailscale.com/envknob"
"tailscale.com/ipn"
"tailscale.com/net/netstat"
"tailscale.com/safesocket"
"tailscale.com/types/logger"
"tailscale.com/util/clientmetric"
"tailscale.com/util/groupmember"
"tailscale.com/util/winutil"
"tailscale.com/version/distro"
)
// ConnIdentity represents the owner of a localhost TCP or unix socket connection
// connecting to the LocalAPI.
type ConnIdentity struct {
conn net.Conn
notWindows bool // runtime.GOOS != "windows"
// Fields used when NotWindows:
isUnixSock bool // Conn is a *net.UnixConn
creds *peercred.Creds // or nil
// Used on Windows:
// TODO(bradfitz): merge these into the peercreds package and
// use that for all.
pid int
userID ipn.WindowsUserID
user *user.User
}
// WindowsUserID returns the local machine's userid of the connection
// if it's on Windows. Otherwise it returns the empty string.
//
// It's suitable for passing to LookupUserFromID (os/user.LookupId) on any
// operating system.
func (ci *ConnIdentity) WindowsUserID() ipn.WindowsUserID {
if envknob.GOOS() != "windows" {
return ""
}
if ci.userID != "" {
return ci.userID
}
// For Linux tests running as Windows:
const isBroken = true // TODO(bradfitz,maisem): fix tests; this doesn't work yet
if ci.creds != nil && !isBroken {
if uid, ok := ci.creds.UserID(); ok {
return ipn.WindowsUserID(uid)
}
}
return ""
}
func (ci *ConnIdentity) User() *user.User { return ci.user }
func (ci *ConnIdentity) Pid() int { return ci.pid }
func (ci *ConnIdentity) IsUnixSock() bool { return ci.isUnixSock }
func (ci *ConnIdentity) Creds() *peercred.Creds { return ci.creds }
var metricIssue869Workaround = clientmetric.NewCounter("issue_869_workaround")
// LookupUserFromID is a wrapper around os/user.LookupId that works around some
// issues on Windows. On non-Windows platforms it's identical to user.LookupId.
func LookupUserFromID(logf logger.Logf, uid string) (*user.User, error) {
u, err := user.LookupId(uid)
if err != nil && runtime.GOOS == "windows" {
// See if uid resolves as a pseudo-user. Temporary workaround until
// https://github.com/golang/go/issues/49509 resolves and ships.
if u, err := winutil.LookupPseudoUser(uid); err == nil {
return u, nil
}
// TODO(aaron): With LookupPseudoUser in place, I don't expect us to reach
// this point anymore. Leaving the below workaround in for now to confirm
// that pseudo-user resolution sufficiently handles this problem.
// The below workaround is only applicable when uid represents a
// valid security principal. Omitting this check causes us to succeed
// even when uid represents a deleted user.
if !winutil.IsSIDValidPrincipal(uid) {
return nil, err
}
metricIssue869Workaround.Add(1)
logf("[warning] issue 869: os/user.LookupId failed; ignoring")
// Work around https://github.com/tailscale/tailscale/issues/869 for
// now. We don't strictly need the username. It's just a nice-to-have.
// So make up a *user.User if their machine is broken in this way.
return &user.User{
Uid: uid,
Username: "unknown-user-" + uid,
Name: "unknown user " + uid,
}, nil
}
return u, err
}
// IsReadonlyConn reports whether the connection should be considered read-only,
// meaning it's not allowed to change the state of the node.
//
// Read-only also means it's not allowed to access sensitive information, which
// admittedly doesn't follow from the name. Consider this "IsUnprivileged".
// Also, Windows doesn't use this. For Windows it always returns false.
//
// TODO(bradfitz): rename it? Also make Windows use this.
func (ci *ConnIdentity) IsReadonlyConn(operatorUID string, logf logger.Logf) bool {
if runtime.GOOS == "windows" {
// Windows doesn't need/use this mechanism, at least yet. It
// has a different last-user-wins auth model.
return false
}
const ro = true
const rw = false
if !safesocket.PlatformUsesPeerCreds() {
return rw
}
creds := ci.creds
if creds == nil {
logf("connection from unknown peer; read-only")
return ro
}
uid, ok := creds.UserID()
if !ok {
logf("connection from peer with unknown userid; read-only")
return ro
}
if uid == "0" {
logf("connection from userid %v; root has access", uid)
return rw
}
if selfUID := os.Getuid(); selfUID != 0 && uid == strconv.Itoa(selfUID) {
logf("connection from userid %v; connection from non-root user matching daemon has access", uid)
return rw
}
if operatorUID != "" && uid == operatorUID {
logf("connection from userid %v; is configured operator", uid)
return rw
}
if yes, err := isLocalAdmin(uid); err != nil {
logf("connection from userid %v; read-only; %v", uid, err)
return ro
} else if yes {
logf("connection from userid %v; is local admin, has access", uid)
return rw
}
logf("connection from userid %v; read-only", uid)
return ro
}
func isLocalAdmin(uid string) (bool, error) {
u, err := user.LookupId(uid)
if err != nil {
return false, err
}
var adminGroup string
switch {
case runtime.GOOS == "darwin":
adminGroup = "admin"
case distro.Get() == distro.QNAP:
adminGroup = "administrators"
default:
return false, fmt.Errorf("no system admin group found")
}
return groupmember.IsMemberOfGroup(adminGroup, u.Username)
}
func peerPid(entries []netstat.Entry, la, ra netip.AddrPort) int {
for _, e := range entries {
if e.Local == ra && e.Remote == la {
return e.Pid
}
}
return 0
}