mirror of https://github.com/tailscale/tailscale/
health: introduce captive-portal-detected Warnable (#12707)
Updates tailscale/tailscale#1634 This PR introduces a new `captive-portal-detected` Warnable which is set to an unhealthy state whenever a captive portal is detected on the local network, preventing Tailscale from connecting. ipn/ipnlocal: fix captive portal loop shutdown Change-Id: I7cafdbce68463a16260091bcec1741501a070c95 net/captivedetection: fix mutex misuse ipn/ipnlocal: ensure that we don't fail to start the timer Change-Id: I3e43fb19264d793e8707c5031c0898e48e3e7465 Signed-off-by: Andrew Dunham <andrew@du.nham.ca> Signed-off-by: Andrea Gottardo <andrea@gottardo.me>pull/12928/merge
Andrea Gottardo
4 months ago
committed by
GitHub
parent
cf97cff33b
commit
90be06bd5b
@ -0,0 +1,217 @@
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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// Package captivedetection provides a way to detect if the system is connected to a network that has
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// a captive portal. It does this by making HTTP requests to known captive portal detection endpoints
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// and checking if the HTTP responses indicate that a captive portal might be present.
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package captivedetection
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import (
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"context"
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"net"
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"net/http"
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"runtime"
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"strings"
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"sync"
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"syscall"
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"time"
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"tailscale.com/net/netmon"
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"tailscale.com/tailcfg"
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"tailscale.com/types/logger"
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)
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// Detector checks whether the system is behind a captive portal.
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type Detector struct {
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// httpClient is the HTTP client that is used for captive portal detection. It is configured
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// to not follow redirects, have a short timeout and no keep-alive.
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httpClient *http.Client
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// currIfIndex is the index of the interface that is currently being used by the httpClient.
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currIfIndex int
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// mu guards currIfIndex.
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mu sync.Mutex
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// logf is the logger used for logging messages. If it is nil, log.Printf is used.
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logf logger.Logf
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}
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// NewDetector creates a new Detector instance for captive portal detection.
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func NewDetector(logf logger.Logf) *Detector {
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d := &Detector{logf: logf}
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d.httpClient = &http.Client{
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// No redirects allowed
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CheckRedirect: func(req *http.Request, via []*http.Request) error {
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return http.ErrUseLastResponse
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},
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Transport: &http.Transport{
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DialContext: d.dialContext,
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DisableKeepAlives: true,
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},
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Timeout: Timeout,
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}
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return d
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}
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// Timeout is the timeout for captive portal detection requests. Because the captive portal intercepting our requests
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// is usually located on the LAN, this is a relatively short timeout.
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const Timeout = 3 * time.Second
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// Detect is the entry point to the API. It attempts to detect if the system is behind a captive portal
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// by making HTTP requests to known captive portal detection Endpoints. If any of the requests return a response code
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// or body that looks like a captive portal, Detect returns true. It returns false in all other cases, including when any
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// error occurs during a detection attempt.
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//
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// This function might take a while to return, as it will attempt to detect a captive portal on all available interfaces
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// by performing multiple HTTP requests. It should be called in a separate goroutine if you want to avoid blocking.
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func (d *Detector) Detect(ctx context.Context, netMon *netmon.Monitor, derpMap *tailcfg.DERPMap, preferredDERPRegionID int) (found bool) {
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return d.detectCaptivePortalWithGOOS(ctx, netMon, derpMap, preferredDERPRegionID, runtime.GOOS)
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}
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func (d *Detector) detectCaptivePortalWithGOOS(ctx context.Context, netMon *netmon.Monitor, derpMap *tailcfg.DERPMap, preferredDERPRegionID int, goos string) (found bool) {
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ifState := netMon.InterfaceState()
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if !ifState.AnyInterfaceUp() {
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d.logf("[v2] DetectCaptivePortal: no interfaces up, returning false")
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return false
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}
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endpoints := availableEndpoints(derpMap, preferredDERPRegionID, d.logf, goos)
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// Here we try detecting a captive portal using *all* available interfaces on the system
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// that have a IPv4 address. We consider to have found a captive portal when any interface
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// reports one may exists. This is necessary because most systems have multiple interfaces,
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// and most importantly on macOS no default route interface is set until the user has accepted
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// the captive portal alert thrown by the system. If no default route interface is known,
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// we need to try with anything that might remotely resemble a Wi-Fi interface.
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for ifName, i := range ifState.Interface {
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if !i.IsUp() || i.IsLoopback() || interfaceNameDoesNotNeedCaptiveDetection(ifName, goos) {
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continue
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}
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addrs, err := i.Addrs()
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if err != nil {
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d.logf("[v1] DetectCaptivePortal: failed to get addresses for interface %s: %v", ifName, err)
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continue
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}
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if len(addrs) == 0 {
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continue
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}
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d.logf("[v2] attempting to do captive portal detection on interface %s", ifName)
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res := d.detectOnInterface(ctx, i.Index, endpoints)
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if res {
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d.logf("DetectCaptivePortal(found=true,ifName=%s)", found, ifName)
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return true
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}
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}
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d.logf("DetectCaptivePortal(found=false)")
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return false
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}
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func interfaceNameDoesNotNeedCaptiveDetection(ifName string, goos string) bool {
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ifName = strings.ToLower(ifName)
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excludedPrefixes := []string{"tailscale", "tun", "tap", "docker", "kube", "wg"}
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if goos == "windows" {
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excludedPrefixes = append(excludedPrefixes, "loopback", "tunnel", "ppp", "isatap", "teredo", "6to4")
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} else if goos == "darwin" || goos == "ios" {
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excludedPrefixes = append(excludedPrefixes, "awdl", "bridge", "ap", "utun", "tap", "llw", "anpi", "lo", "stf", "gif", "xhc")
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}
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for _, prefix := range excludedPrefixes {
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if strings.HasPrefix(ifName, prefix) {
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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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// detectOnInterface reports whether or not we think the system is behind a
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// captive portal, detected by making a request to a URL that we know should
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// return a "204 No Content" response and checking if that's what we get.
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//
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// The boolean return is whether we think we have a captive portal.
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func (d *Detector) detectOnInterface(ctx context.Context, ifIndex int, endpoints []Endpoint) bool {
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defer d.httpClient.CloseIdleConnections()
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d.logf("[v2] %d available captive portal detection endpoints: %v", len(endpoints), endpoints)
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// We try to detect the captive portal more quickly by making requests to multiple endpoints concurrently.
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var wg sync.WaitGroup
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resultCh := make(chan bool, len(endpoints))
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for i, e := range endpoints {
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if i >= 5 {
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// Try a maximum of 5 endpoints, break out (returning false) if we run of attempts.
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break
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}
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wg.Add(1)
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go func(endpoint Endpoint) {
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defer wg.Done()
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found, err := d.verifyCaptivePortalEndpoint(ctx, endpoint, ifIndex)
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if err != nil {
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d.logf("[v1] checkCaptivePortalEndpoint failed with endpoint %v: %v", endpoint, err)
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return
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}
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if found {
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resultCh <- true
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}
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}(e)
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}
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go func() {
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wg.Wait()
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close(resultCh)
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}()
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for result := range resultCh {
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if result {
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// If any of the endpoints seems to be a captive portal, we consider the system to be behind one.
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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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// verifyCaptivePortalEndpoint checks if the given Endpoint is a captive portal by making an HTTP request to the
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// given Endpoint URL using the interface with index ifIndex, and checking if the response looks like a captive portal.
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func (d *Detector) verifyCaptivePortalEndpoint(ctx context.Context, e Endpoint, ifIndex int) (found bool, err error) {
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req, err := http.NewRequestWithContext(ctx, "GET", e.URL.String(), nil)
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if err != nil {
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return false, err
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}
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// Attach the Tailscale challenge header if the endpoint supports it. Not all captive portal detection endpoints
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// support this, so we only attach it if the endpoint does.
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if e.SupportsTailscaleChallenge {
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// Note: the set of valid characters in a challenge and the total
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// length is limited; see isChallengeChar in cmd/derper for more
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// details.
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chal := "ts_" + e.URL.Host
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req.Header.Set("X-Tailscale-Challenge", chal)
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}
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d.mu.Lock()
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d.currIfIndex = ifIndex
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d.mu.Unlock()
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// Make the actual request, and check if the response looks like a captive portal or not.
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r, err := d.httpClient.Do(req)
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if err != nil {
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return false, err
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}
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return e.responseLooksLikeCaptive(r, d.logf), nil
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}
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func (d *Detector) dialContext(ctx context.Context, network, addr string) (net.Conn, error) {
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d.mu.Lock()
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defer d.mu.Unlock()
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ifIndex := d.currIfIndex
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dl := net.Dialer{
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Control: func(network, address string, c syscall.RawConn) error {
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return setSocketInterfaceIndex(c, ifIndex, d.logf)
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},
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}
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return dl.DialContext(ctx, network, addr)
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}
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package captivedetection
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import (
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"context"
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"runtime"
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"sync"
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"testing"
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"tailscale.com/net/netmon"
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)
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func TestAvailableEndpointsAlwaysAtLeastTwo(t *testing.T) {
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endpoints := availableEndpoints(nil, 0, t.Logf, runtime.GOOS)
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if len(endpoints) == 0 {
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t.Errorf("Expected non-empty AvailableEndpoints, got an empty slice instead")
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}
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if len(endpoints) == 1 {
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t.Errorf("Expected at least two AvailableEndpoints for redundancy, got only one instead")
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}
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for _, e := range endpoints {
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if e.URL.Scheme != "http" {
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t.Errorf("Expected HTTP URL in Endpoint, got HTTPS")
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}
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}
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}
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func TestDetectCaptivePortalReturnsFalse(t *testing.T) {
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d := NewDetector(t.Logf)
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found := d.Detect(context.Background(), netmon.NewStatic(), nil, 0)
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if found {
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t.Errorf("DetectCaptivePortal returned true, expected false.")
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}
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}
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func TestAllEndpointsAreUpAndReturnExpectedResponse(t *testing.T) {
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d := NewDetector(t.Logf)
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endpoints := availableEndpoints(nil, 0, t.Logf, runtime.GOOS)
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var wg sync.WaitGroup
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for _, e := range endpoints {
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wg.Add(1)
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go func(endpoint Endpoint) {
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defer wg.Done()
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found, err := d.verifyCaptivePortalEndpoint(context.Background(), endpoint, 0)
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if err != nil {
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t.Errorf("verifyCaptivePortalEndpoint failed with endpoint %v: %v", endpoint, err)
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}
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if found {
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t.Errorf("verifyCaptivePortalEndpoint with endpoint %v says we're behind a captive portal, but we aren't", endpoint)
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}
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}(e)
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}
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wg.Wait()
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}
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package captivedetection
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import (
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"cmp"
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"fmt"
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"io"
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"net/http"
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"net/url"
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"slices"
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"go4.org/mem"
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"tailscale.com/net/dnsfallback"
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"tailscale.com/tailcfg"
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"tailscale.com/types/logger"
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)
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// EndpointProvider is an enum that represents the source of an Endpoint.
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type EndpointProvider int
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const (
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// DERPMapPreferred is used for an endpoint that is a DERP node contained in the current preferred DERP region,
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// as provided by the DERPMap.
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DERPMapPreferred EndpointProvider = iota
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// DERPMapOther is used for an endpoint that is a DERP node, but not contained in the current preferred DERP region.
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DERPMapOther
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// Tailscale is used for endpoints that are the Tailscale coordination server or admin console.
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Tailscale
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)
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func (p EndpointProvider) String() string {
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switch p {
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case DERPMapPreferred:
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return "DERPMapPreferred"
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case Tailscale:
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return "Tailscale"
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case DERPMapOther:
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return "DERPMapOther"
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default:
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return fmt.Sprintf("EndpointProvider(%d)", p)
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}
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}
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// Endpoint represents a URL that can be used to detect a captive portal, along with the expected
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// result of the HTTP request.
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type Endpoint struct {
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// URL is the URL that we make an HTTP request to as part of the captive portal detection process.
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URL *url.URL
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// StatusCode is the expected HTTP status code that we expect to see in the response.
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StatusCode int
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// ExpectedContent is a string that we expect to see contained in the response body. If this is non-empty,
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// we will check that the response body contains this string. If it is empty, we will not check the response body
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// and only check the status code.
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ExpectedContent string
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// SupportsTailscaleChallenge is true if the endpoint will return the sent value of the X-Tailscale-Challenge
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// HTTP header in its HTTP response.
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SupportsTailscaleChallenge bool
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// Provider is the source of the endpoint. This is used to prioritize certain endpoints over others
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// (for example, a DERP node in the preferred region should always be used first).
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Provider EndpointProvider
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}
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func (e Endpoint) String() string {
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return fmt.Sprintf("Endpoint{URL=%q, StatusCode=%d, ExpectedContent=%q, SupportsTailscaleChallenge=%v, Provider=%s}", e.URL, e.StatusCode, e.ExpectedContent, e.SupportsTailscaleChallenge, e.Provider.String())
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}
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func (e Endpoint) Equal(other Endpoint) bool {
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return e.URL.String() == other.URL.String() &&
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e.StatusCode == other.StatusCode &&
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e.ExpectedContent == other.ExpectedContent &&
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e.SupportsTailscaleChallenge == other.SupportsTailscaleChallenge &&
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e.Provider == other.Provider
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}
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// availableEndpoints returns a set of Endpoints which can be used for captive portal detection by performing
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// one or more HTTP requests and looking at the response. The returned Endpoints are ordered by preference,
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// with the most preferred Endpoint being the first in the slice.
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func availableEndpoints(derpMap *tailcfg.DERPMap, preferredDERPRegionID int, logf logger.Logf, goos string) []Endpoint {
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endpoints := []Endpoint{}
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if derpMap == nil || len(derpMap.Regions) == 0 {
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||||||
|
// When the client first starts, we don't have a DERPMap in LocalBackend yet. In this case,
|
||||||
|
// we use the static DERPMap from dnsfallback.
|
||||||
|
logf("captivedetection: current DERPMap is empty, using map from dnsfallback")
|
||||||
|
derpMap = dnsfallback.GetDERPMap()
|
||||||
|
}
|
||||||
|
// Use the DERP IPs as captive portal detection endpoints. Using IPs is better than hostnames
|
||||||
|
// because they do not depend on DNS resolution.
|
||||||
|
for _, region := range derpMap.Regions {
|
||||||
|
if region.Avoid {
|
||||||
|
continue
|
||||||
|
}
|
||||||
|
for _, node := range region.Nodes {
|
||||||
|
if node.IPv4 == "" || !node.CanPort80 {
|
||||||
|
continue
|
||||||
|
}
|
||||||
|
str := "http://" + node.IPv4 + "/generate_204"
|
||||||
|
u, err := url.Parse(str)
|
||||||
|
if err != nil {
|
||||||
|
logf("captivedetection: failed to parse DERP node URL %q: %v", str, err)
|
||||||
|
continue
|
||||||
|
}
|
||||||
|
p := DERPMapOther
|
||||||
|
if region.RegionID == preferredDERPRegionID {
|
||||||
|
p = DERPMapPreferred
|
||||||
|
}
|
||||||
|
e := Endpoint{u, http.StatusNoContent, "", true, p}
|
||||||
|
endpoints = append(endpoints, e)
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
// Let's also try the default Tailscale coordination server and admin console.
|
||||||
|
// These are likely to be blocked on some networks.
|
||||||
|
appendTailscaleEndpoint := func(urlString string) {
|
||||||
|
u, err := url.Parse(urlString)
|
||||||
|
if err != nil {
|
||||||
|
logf("captivedetection: failed to parse Tailscale URL %q: %v", urlString, err)
|
||||||
|
return
|
||||||
|
}
|
||||||
|
endpoints = append(endpoints, Endpoint{u, http.StatusNoContent, "", false, Tailscale})
|
||||||
|
}
|
||||||
|
appendTailscaleEndpoint("http://controlplane.tailscale.com/generate_204")
|
||||||
|
appendTailscaleEndpoint("http://login.tailscale.com/generate_204")
|
||||||
|
|
||||||
|
// Sort the endpoints by provider so that we can prioritize DERP nodes in the preferred region, followed by
|
||||||
|
// any other DERP server elsewhere, then followed by Tailscale endpoints.
|
||||||
|
slices.SortFunc(endpoints, func(x, y Endpoint) int {
|
||||||
|
return cmp.Compare(x.Provider, y.Provider)
|
||||||
|
})
|
||||||
|
|
||||||
|
return endpoints
|
||||||
|
}
|
||||||
|
|
||||||
|
// responseLooksLikeCaptive checks if the given HTTP response matches the expected response for the Endpoint.
|
||||||
|
func (e Endpoint) responseLooksLikeCaptive(r *http.Response, logf logger.Logf) bool {
|
||||||
|
defer r.Body.Close()
|
||||||
|
|
||||||
|
// Check the status code first.
|
||||||
|
if r.StatusCode != e.StatusCode {
|
||||||
|
logf("[v1] unexpected status code in captive portal response: want=%d, got=%d", e.StatusCode, r.StatusCode)
|
||||||
|
return true
|
||||||
|
}
|
||||||
|
|
||||||
|
// If the endpoint supports the Tailscale challenge header, check that the response contains the expected header.
|
||||||
|
if e.SupportsTailscaleChallenge {
|
||||||
|
expectedResponse := "response ts_" + e.URL.Host
|
||||||
|
hasResponse := r.Header.Get("X-Tailscale-Response") == expectedResponse
|
||||||
|
if !hasResponse {
|
||||||
|
// The response did not contain the expected X-Tailscale-Response header, which means we are most likely
|
||||||
|
// behind a captive portal (somebody is tampering with the response headers).
|
||||||
|
logf("captive portal check response did not contain expected X-Tailscale-Response header: want=%q, got=%q", expectedResponse, r.Header.Get("X-Tailscale-Response"))
|
||||||
|
return true
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
// If we don't have an expected content string, we don't need to check the response body.
|
||||||
|
if e.ExpectedContent == "" {
|
||||||
|
return false
|
||||||
|
}
|
||||||
|
|
||||||
|
// Read the response body and check if it contains the expected content.
|
||||||
|
b, err := io.ReadAll(io.LimitReader(r.Body, 4096))
|
||||||
|
if err != nil {
|
||||||
|
logf("reading captive portal check response body failed: %v", err)
|
||||||
|
return false
|
||||||
|
}
|
||||||
|
hasExpectedContent := mem.Contains(mem.B(b), mem.S(e.ExpectedContent))
|
||||||
|
if !hasExpectedContent {
|
||||||
|
// The response body did not contain the expected content, that means we are most likely behind a captive portal.
|
||||||
|
logf("[v1] captive portal check response body did not contain expected content: want=%q", e.ExpectedContent)
|
||||||
|
return true
|
||||||
|
}
|
||||||
|
|
||||||
|
// If we got here, the response looks good.
|
||||||
|
return false
|
||||||
|
}
|
||||||
@ -0,0 +1,19 @@
|
|||||||
|
// Copyright (c) Tailscale Inc & AUTHORS
|
||||||
|
// SPDX-License-Identifier: BSD-3-Clause
|
||||||
|
|
||||||
|
//go:build !(ios || darwin)
|
||||||
|
|
||||||
|
package captivedetection
|
||||||
|
|
||||||
|
import (
|
||||||
|
"syscall"
|
||||||
|
|
||||||
|
"tailscale.com/types/logger"
|
||||||
|
)
|
||||||
|
|
||||||
|
// setSocketInterfaceIndex sets the IP_BOUND_IF socket option on the given RawConn.
|
||||||
|
// This forces the socket to use the given interface.
|
||||||
|
func setSocketInterfaceIndex(c syscall.RawConn, ifIndex int, logf logger.Logf) error {
|
||||||
|
// No-op on non-Darwin platforms.
|
||||||
|
return nil
|
||||||
|
}
|
||||||
@ -0,0 +1,24 @@
|
|||||||
|
// Copyright (c) Tailscale Inc & AUTHORS
|
||||||
|
// SPDX-License-Identifier: BSD-3-Clause
|
||||||
|
|
||||||
|
//go:build ios || darwin
|
||||||
|
|
||||||
|
package captivedetection
|
||||||
|
|
||||||
|
import (
|
||||||
|
"syscall"
|
||||||
|
|
||||||
|
"golang.org/x/sys/unix"
|
||||||
|
"tailscale.com/types/logger"
|
||||||
|
)
|
||||||
|
|
||||||
|
// setSocketInterfaceIndex sets the IP_BOUND_IF socket option on the given RawConn.
|
||||||
|
// This forces the socket to use the given interface.
|
||||||
|
func setSocketInterfaceIndex(c syscall.RawConn, ifIndex int, logf logger.Logf) error {
|
||||||
|
return c.Control((func(fd uintptr) {
|
||||||
|
err := unix.SetsockoptInt(int(fd), unix.IPPROTO_IP, unix.IP_BOUND_IF, ifIndex)
|
||||||
|
if err != nil {
|
||||||
|
logf("captivedetection: failed to set IP_BOUND_IF (ifIndex=%d): %v", ifIndex, err)
|
||||||
|
}
|
||||||
|
}))
|
||||||
|
}
|
||||||
Loading…
Reference in New Issue