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tailscale/client/web/auth.go

340 lines
11 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package web
import (
"context"
"crypto/rand"
"encoding/base64"
"errors"
"fmt"
"net/http"
"net/url"
"slices"
"strings"
"time"
"tailscale.com/client/tailscale/apitype"
"tailscale.com/ipn/ipnstate"
"tailscale.com/tailcfg"
)
const (
sessionCookieName = "TS-Web-Session"
sessionCookieExpiry = time.Hour * 24 * 30 // 30 days
)
// browserSession holds data about a user's browser session
// on the full management web client.
type browserSession struct {
// ID is the unique identifier for the session.
// It is passed in the user's "TS-Web-Session" browser cookie.
ID string
SrcNode tailcfg.NodeID
SrcUser tailcfg.UserID
AuthID string // from tailcfg.WebClientAuthResponse
AuthURL string // from tailcfg.WebClientAuthResponse
Created time.Time
Authenticated bool
}
// isAuthorized reports true if the given session is authorized
// to be used by its associated user to access the full management
// web client.
//
// isAuthorized is true only when s.Authenticated is true (i.e.
// the user has authenticated the session) and the session is not
// expired.
// 2023-10-05: Sessions expire by default 30 days after creation.
func (s *browserSession) isAuthorized(now time.Time) bool {
switch {
case s == nil:
return false
case !s.Authenticated:
return false // awaiting auth
case s.isExpired(now):
return false // expired
}
return true
}
// isExpired reports true if s is expired.
// 2023-10-05: Sessions expire by default 30 days after creation.
func (s *browserSession) isExpired(now time.Time) bool {
return !s.Created.IsZero() && now.After(s.expires())
}
// expires reports when the given session expires.
func (s *browserSession) expires() time.Time {
return s.Created.Add(sessionCookieExpiry)
}
var (
errNoSession = errors.New("no-browser-session")
errNotUsingTailscale = errors.New("not-using-tailscale")
errTaggedRemoteSource = errors.New("tagged-remote-source")
errTaggedLocalSource = errors.New("tagged-local-source")
errNotOwner = errors.New("not-owner")
)
// getSession retrieves the browser session associated with the request,
// if one exists.
//
// An error is returned in any of the following cases:
//
// - (errNotUsingTailscale) The request was not made over tailscale.
//
// - (errNoSession) The request does not have a session.
//
// - (errTaggedRemoteSource) The source is remote (another node) and tagged.
// Users must use their own user-owned devices to manage other nodes'
// web clients.
//
// - (errTaggedLocalSource) The source is local (the same node) and tagged.
// Tagged nodes can only be remotely managed, allowing ACLs to dictate
// access to web clients.
//
// - (errNotOwner) The source is not the owner of this client (if the
// client is user-owned). Only the owner is allowed to manage the
// node via the web client.
//
// If no error is returned, the browserSession is always non-nil.
// getTailscaleBrowserSession does not check whether the session has been
// authorized by the user. Callers can use browserSession.isAuthorized.
//
// The WhoIsResponse is always populated, with a non-nil Node and UserProfile,
// unless getTailscaleBrowserSession reports errNotUsingTailscale.
func (s *Server) getSession(r *http.Request) (*browserSession, *apitype.WhoIsResponse, *ipnstate.Status, error) {
whoIs, whoIsErr := s.lc.WhoIs(r.Context(), r.RemoteAddr)
status, statusErr := s.lc.StatusWithoutPeers(r.Context())
switch {
case whoIsErr != nil:
return nil, nil, status, errNotUsingTailscale
case statusErr != nil:
return nil, whoIs, nil, statusErr
case status.Self == nil:
return nil, whoIs, status, errors.New("missing self node in tailscale status")
case whoIs.Node.IsTagged() && whoIs.Node.StableID == status.Self.ID:
return nil, whoIs, status, errTaggedLocalSource
case whoIs.Node.IsTagged():
return nil, whoIs, status, errTaggedRemoteSource
case !status.Self.IsTagged() && status.Self.UserID != whoIs.UserProfile.ID:
return nil, whoIs, status, errNotOwner
}
srcNode := whoIs.Node.ID
srcUser := whoIs.UserProfile.ID
cookie, err := r.Cookie(sessionCookieName)
if errors.Is(err, http.ErrNoCookie) {
return nil, whoIs, status, errNoSession
} else if err != nil {
return nil, whoIs, status, err
}
v, ok := s.browserSessions.Load(cookie.Value)
if !ok {
return nil, whoIs, status, errNoSession
}
session := v.(*browserSession)
if session.SrcNode != srcNode || session.SrcUser != srcUser {
// In this case the browser cookie is associated with another tailscale node.
// Maybe the source browser's machine was logged out and then back in as a different node.
// Return errNoSession because there is no session for this user.
return nil, whoIs, status, errNoSession
} else if session.isExpired(s.timeNow()) {
// Session expired, remove from session map and return errNoSession.
s.browserSessions.Delete(session.ID)
return nil, whoIs, status, errNoSession
}
return session, whoIs, status, nil
}
// newSession creates a new session associated with the given source user/node,
// and stores it back to the session cache. Creating of a new session includes
// generating a new auth URL from the control server.
func (s *Server) newSession(ctx context.Context, src *apitype.WhoIsResponse) (*browserSession, error) {
sid, err := s.newSessionID()
if err != nil {
return nil, err
}
session := &browserSession{
ID: sid,
SrcNode: src.Node.ID,
SrcUser: src.UserProfile.ID,
Created: s.timeNow(),
}
if s.controlSupportsCheckMode(ctx) {
// control supports check mode, so get a new auth URL and return.
a, err := s.newAuthURL(ctx, src.Node.ID)
if err != nil {
return nil, err
}
session.AuthID = a.ID
session.AuthURL = a.URL
} else {
// control does not support check mode, so there is no additional auth we can do.
session.Authenticated = true
}
s.browserSessions.Store(sid, session)
return session, nil
}
// controlSupportsCheckMode returns whether the current control server supports web client check mode, to verify a user's identity.
// We assume that only "tailscale.com" control servers support check mode.
// This allows the web client to be used with non-standard control servers.
// If an error occurs getting the control URL, this method returns true to fail closed.
//
// TODO(juanfont/headscale#1623): adjust or remove this when headscale supports check mode.
func (s *Server) controlSupportsCheckMode(ctx context.Context) bool {
prefs, err := s.lc.GetPrefs(ctx)
if err != nil {
return true
}
controlURL, err := url.Parse(prefs.ControlURLOrDefault())
if err != nil {
return true
}
return strings.HasSuffix(controlURL.Host, ".tailscale.com")
}
// awaitUserAuth blocks until the given session auth has been completed
// by the user on the control server, then updates the session cache upon
// completion. An error is returned if control auth failed for any reason.
func (s *Server) awaitUserAuth(ctx context.Context, session *browserSession) error {
if session.isAuthorized(s.timeNow()) {
return nil // already authorized
}
a, err := s.waitAuthURL(ctx, session.AuthID, session.SrcNode)
if err != nil {
// Clean up the session. Doing this on any error from control
// server to avoid the user getting stuck with a bad session
// cookie.
s.browserSessions.Delete(session.ID)
return err
}
if a.Complete {
session.Authenticated = a.Complete
s.browserSessions.Store(session.ID, session)
}
return nil
}
func (s *Server) newSessionID() (string, error) {
raw := make([]byte, 16)
for i := 0; i < 5; i++ {
if _, err := rand.Read(raw); err != nil {
return "", err
}
cookie := "ts-web-" + base64.RawURLEncoding.EncodeToString(raw)
if _, ok := s.browserSessions.Load(cookie); !ok {
return cookie, nil
}
}
return "", errors.New("too many collisions generating new session; please refresh page")
}
// peerCapabilities holds information about what a source
// peer is allowed to edit via the web UI.
//
// map value is true if the peer can edit the given feature.
// Only capFeatures included in validCaps will be included.
type peerCapabilities map[capFeature]bool
// canEdit is true if the peerCapabilities grant edit access
// to the given feature.
func (p peerCapabilities) canEdit(feature capFeature) bool {
if p == nil {
return false
}
if p[capFeatureAll] {
return true
}
return p[feature]
}
// isEmpty is true if p is either nil or has no capabilities
// with value true.
func (p peerCapabilities) isEmpty() bool {
if p == nil {
return true
}
for _, v := range p {
if v == true {
return false
}
}
return true
}
type capFeature string
const (
// The following values should not be edited.
// New caps can be added, but existing ones should not be changed,
// as these exact values are used by users in tailnet policy files.
//
// IMPORTANT: When adding a new cap, also update validCaps slice below.
capFeatureAll capFeature = "*" // grants peer management of all features
capFeatureSSH capFeature = "ssh" // grants peer SSH server management
capFeatureSubnets capFeature = "subnets" // grants peer subnet routes management
capFeatureExitNodes capFeature = "exitnodes" // grants peer ability to advertise-as and use exit nodes
capFeatureAccount capFeature = "account" // grants peer ability to turn on auto updates and log out of node
)
// validCaps contains the list of valid capabilities used in the web client.
// Any capabilities included in a peer's grants that do not fall into this
// list will be ignored.
var validCaps []capFeature = []capFeature{
capFeatureAll,
capFeatureSSH,
capFeatureSubnets,
capFeatureExitNodes,
capFeatureAccount,
}
type capRule struct {
CanEdit []string `json:"canEdit,omitempty"` // list of features peer is allowed to edit
}
// toPeerCapabilities parses out the web ui capabilities from the
// given whois response.
func toPeerCapabilities(status *ipnstate.Status, whois *apitype.WhoIsResponse) (peerCapabilities, error) {
if whois == nil || status == nil {
return peerCapabilities{}, nil
}
if whois.Node.IsTagged() {
// We don't allow management *from* tagged nodes, so ignore caps.
// The web client auth flow relies on having a true user identity
// that can be verified through login.
return peerCapabilities{}, nil
}
if !status.Self.IsTagged() {
// User owned nodes are only ever manageable by the owner.
if status.Self.UserID != whois.UserProfile.ID {
return peerCapabilities{}, nil
} else {
return peerCapabilities{capFeatureAll: true}, nil // owner can edit all features
}
}
// For tagged nodes, we actually look at the granted capabilities.
caps := peerCapabilities{}
rules, err := tailcfg.UnmarshalCapJSON[capRule](whois.CapMap, tailcfg.PeerCapabilityWebUI)
if err != nil {
return nil, fmt.Errorf("failed to unmarshal capability: %v", err)
}
for _, c := range rules {
for _, f := range c.CanEdit {
cap := capFeature(strings.ToLower(f))
if slices.Contains(validCaps, cap) {
caps[cap] = true
}
}
}
return caps, nil
}