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tsweb: add EnforceHostname helper for DNS rebinding mitigation
Signed-off-by: Will Norris <will@tailscale.com>
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parent
b45b948776
commit
f9fa174e11
@ -25,9 +25,11 @@
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"strconv"
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"strconv"
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"strings"
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"strings"
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"sync"
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"sync"
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"sync/atomic"
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"time"
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"time"
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"go4.org/mem"
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"go4.org/mem"
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"tailscale.com/client/tailscale"
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"tailscale.com/envknob"
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"tailscale.com/envknob"
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"tailscale.com/metrics"
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"tailscale.com/metrics"
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"tailscale.com/net/tsaddr"
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"tailscale.com/net/tsaddr"
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@ -779,3 +781,67 @@ func (r expVarPromStructRoot) String() string { panic("unused
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_ PrometheusMetricsReflectRooter = expVarPromStructRoot{}
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_ PrometheusMetricsReflectRooter = expVarPromStructRoot{}
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_ expvar.Var = expVarPromStructRoot{}
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_ expvar.Var = expVarPromStructRoot{}
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)
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)
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type hostEnforcer struct {
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expiry time.Time
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hosts []string
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once sync.Once
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}
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func (he *hostEnforcer) allowedHosts(ctx context.Context, client *tailscale.LocalClient) ([]string, error) {
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var statusErr error
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he.once.Do(func() {
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status, err := client.StatusWithoutPeers(ctx)
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if err != nil {
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statusErr = err
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return
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}
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dnsName := strings.TrimSuffix(status.Self.DNSName, ".") // node.tailnet.ts.net
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bareHost := strings.TrimSuffix(dnsName, "."+status.MagicDNSSuffix) // node
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he.hosts = []string{dnsName, bareHost}
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})
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if statusErr != nil {
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return nil, statusErr
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}
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return he.hosts, nil
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}
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// EnforceHostname wraps a handler and enforces that all inbound requests have a Host header that matches the local Tailscale node.
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// Acceptable Host headers are bare IP addresses, the node's full DNS name (node.tailnet.ts.net) and the node's bare hostname.
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// This is used to help protect against DNS rebinding attacks.
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// If client is nil, a default client will be used.
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func EnforceHostname(h http.Handler, client *tailscale.LocalClient) http.Handler {
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if client == nil {
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client = &tailscale.LocalClient{}
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}
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enforcerAtomic := atomic.Pointer[hostEnforcer]{}
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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// always allow bare IP addresses
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if _, err := netip.ParseAddr(r.Host); err == nil {
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h.ServeHTTP(w, r)
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return
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}
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enforcer := enforcerAtomic.Load()
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// refresh the list of allowed hosts every 5 seconds
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if now := time.Now(); enforcer == nil || now.After(enforcer.expiry) {
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newEnforcer := &hostEnforcer{expiry: now.Add(5 * time.Second)}
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if enforcerAtomic.CompareAndSwap(enforcer, newEnforcer) {
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enforcer = enforcerAtomic.Load()
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}
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}
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allowedHosts, err := enforcer.allowedHosts(r.Context(), client)
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if err != nil {
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http.Error(w, "unable to get tailscale status", http.StatusInternalServerError)
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return
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}
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for _, host := range allowedHosts {
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if r.Host == host {
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h.ServeHTTP(w, r)
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return
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}
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}
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http.Error(w, "invalid Host header", http.StatusBadRequest)
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})
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}
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