client/tailscale/apitype: add LocalAPIHost const, use it

Removes duplication.

Updates tailcale/corp#7948

Change-Id: I564c912ecfde31ba2293124bb1316e433c2a10f1
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

client/tailscale/apitype/apitype.go

@@ -7,6 +7,9 @@ package apitype
 
 import "tailscale.com/tailcfg"
 
+// LocalAPIHost is the Host header value used by the LocalAPI.
+const LocalAPIHost = "local-tailscaled.sock"
+
 // WhoIsResponse is the JSON type returned by tailscaled debug server's /whois?ip=$IP handler.
 type WhoIsResponse struct {
 	Node        *tailcfg.Node

client/tailscale/localclient.go

@@ -200,7 +200,7 @@ func (lc *LocalClient) send(ctx context.Context, method, path string, wantStatus
 	if jr, ok := body.(jsonReader); ok && jr.err != nil {
 		return nil, jr.err // fail early if there was a JSON marshaling error
 	}
-	req, err := http.NewRequestWithContext(ctx, method, "http://local-tailscaled.sock"+path, body)
+	req, err := http.NewRequestWithContext(ctx, method, "http://"+apitype.LocalAPIHost+path, body)
 	if err != nil {
 		return nil, err
 	}
@@ -440,7 +440,7 @@ func (lc *LocalClient) DeleteWaitingFile(ctx context.Context, baseName string) e
 }
 
 func (lc *LocalClient) GetWaitingFile(ctx context.Context, baseName string) (rc io.ReadCloser, size int64, err error) {
-	req, err := http.NewRequestWithContext(ctx, "GET", "http://local-tailscaled.sock/localapi/v0/files/"+url.PathEscape(baseName), nil)
+	req, err := http.NewRequestWithContext(ctx, "GET", "http://"+apitype.LocalAPIHost+"/localapi/v0/files/"+url.PathEscape(baseName), nil)
 	if err != nil {
 		return nil, 0, err
 	}
@@ -473,7 +473,7 @@ func (lc *LocalClient) FileTargets(ctx context.Context) ([]apitype.FileTarget, e
 // A size of -1 means unknown.
 // The name parameter is the original filename, not escaped.
 func (lc *LocalClient) PushFile(ctx context.Context, target tailcfg.StableNodeID, size int64, name string, r io.Reader) error {
-	req, err := http.NewRequestWithContext(ctx, "PUT", "http://local-tailscaled.sock/localapi/v0/file-put/"+string(target)+"/"+url.PathEscape(name), r)
+	req, err := http.NewRequestWithContext(ctx, "PUT", "http://"+apitype.LocalAPIHost+"/localapi/v0/file-put/"+string(target)+"/"+url.PathEscape(name), r)
 	if err != nil {
 		return err
 	}
@@ -584,7 +584,7 @@ func (lc *LocalClient) DialTCP(ctx context.Context, host string, port uint16) (n
 		},
 	}
 	ctx = httptrace.WithClientTrace(ctx, &trace)
-	req, err := http.NewRequestWithContext(ctx, "POST", "http://local-tailscaled.sock/localapi/v0/dial", nil)
+	req, err := http.NewRequestWithContext(ctx, "POST", "http://"+apitype.LocalAPIHost+"/localapi/v0/dial", nil)
 	if err != nil {
 		return nil, err
 	}

ipn/localapi/localapi.go

@@ -34,6 +34,7 @@ import (
 	"tailscale.com/ipn/ipnlocal"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/net/netutil"
+	"tailscale.com/safesocket"
 	"tailscale.com/tailcfg"
 	"tailscale.com/tka"
 	"tailscale.com/types/key"
@@ -137,6 +138,10 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "server has no local backend", http.StatusInternalServerError)
 		return
 	}
+	if r.Referer() != "" || r.Header.Get("Origin") != "" || !validHost(r.Host) {
+		http.Error(w, "invalid localapi request", http.StatusForbidden)
+		return
+	}
 	w.Header().Set("Tailscale-Version", version.Long)
 	if h.RequiredPassword != "" {
 		_, pass, ok := r.BasicAuth()
@@ -156,6 +161,24 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+// validHost reports whether h is a valid Host header value for a LocalAPI request.
+func validHost(h string) bool {
+	// The client code sends a hostname of "local-tailscaled.sock".
+	switch h {
+	case "", apitype.LocalAPIHost:
+		return true
+	}
+	// Otherwise, any Host header we see should at most be an ip:port.
+	ap, err := netip.ParseAddrPort(h)
+	if err != nil {
+		return false
+	}
+	if runtime.GOOS == "windows" && ap.Port() != safesocket.WindowsLocalPort {
+		return false
+	}
+	return ap.Addr().IsLoopback()
+}
+
 // handlerForPath returns the LocalAPI handler for the provided Request.URI.Path.
 // (the path doesn't include any query parameters)
 func handlerForPath(urlPath string) (h localAPIHandler, ok bool) {