admin: Enforce and refactor origin checking

Using URLs seems a little cleaner and more correct

cf: https://caddy.community/t/protect-admin-endpoint/15114

(This used to work. Something must have changed recently.)

admin.go

@@ -42,6 +42,7 @@ import (
 	"github.com/caddyserver/certmagic"
 	"github.com/prometheus/client_golang/prometheus"
 	"go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
 )
 
 // AdminConfig configures Caddy's API endpoint, which is used
@@ -192,6 +193,7 @@ func (admin AdminConfig) newAdminHandler(addr NetworkAddress, remote bool) admin
 	} else {
 		muxWrap.enforceHost = !addr.isWildcardInterface()
 		muxWrap.allowedOrigins = admin.allowedOrigins(addr)
+		muxWrap.enforceOrigin = admin.EnforceOrigin
 	}
 
 	addRouteWithMetrics := func(pattern string, handlerLabel string, h http.Handler) {
@@ -252,7 +254,7 @@ func (admin AdminConfig) newAdminHandler(addr NetworkAddress, remote bool) admin
 // will be used as the default origin. If admin.Origins is
 // empty, no origins will be allowed, effectively bricking the
 // endpoint for non-unix-socket endpoints, but whatever.
-func (admin AdminConfig) allowedOrigins(addr NetworkAddress) []string {
+func (admin AdminConfig) allowedOrigins(addr NetworkAddress) []*url.URL {
 	uniqueOrigins := make(map[string]struct{})
 	for _, o := range admin.Origins {
 		uniqueOrigins[o] = struct{}{}
@@ -276,8 +278,23 @@ func (admin AdminConfig) allowedOrigins(addr NetworkAddress) []string {
 			uniqueOrigins[addr.JoinHostPort(0)] = struct{}{}
 		}
 	}
-	allowed := make([]string, 0, len(uniqueOrigins))
-	for origin := range uniqueOrigins {
+	allowed := make([]*url.URL, 0, len(uniqueOrigins))
+	for originStr := range uniqueOrigins {
+		var origin *url.URL
+		if strings.Contains(originStr, "://") {
+			var err error
+			origin, err = url.Parse(originStr)
+			if err != nil {
+				continue
+			}
+			origin.Path = ""
+			origin.RawPath = ""
+			origin.Fragment = ""
+			origin.RawFragment = ""
+			origin.RawQuery = ""
+		} else {
+			origin = &url.URL{Host: originStr}
+		}
 		allowed = append(allowed, origin)
 	}
 	return allowed
@@ -358,7 +375,7 @@ func replaceLocalAdminServer(cfg *Config) error {
 	adminLogger.Info("admin endpoint started",
 		zap.String("address", addr.String()),
 		zap.Bool("enforce_origin", adminConfig.EnforceOrigin),
-		zap.Strings("origins", handler.allowedOrigins))
+		zap.Array("origins", loggableURLArray(handler.allowedOrigins)))
 
 	if !handler.enforceHost {
 		adminLogger.Warn("admin endpoint on open interface; host checking disabled",
@@ -650,10 +667,10 @@ type AdminRoute struct {
 type adminHandler struct {
 	mux *http.ServeMux
 
-	// security for local/plaintext) endpoint, on by default
+	// security for local/plaintext endpoint
 	enforceOrigin  bool
 	enforceHost    bool
-	allowedOrigins []string
+	allowedOrigins []*url.URL
 
 	// security for remote/encrypted endpoint
 	remoteControl *RemoteAdmin
@@ -779,8 +796,8 @@ func (h adminHandler) handleError(w http.ResponseWriter, r *http.Request, err er
 // rebinding attacks.
 func (h adminHandler) checkHost(r *http.Request) error {
 	var allowed bool
-	for _, allowedHost := range h.allowedOrigins {
-		if r.Host == allowedHost {
+	for _, allowedOrigin := range h.allowedOrigins {
+		if r.Host == allowedOrigin.Host {
 			allowed = true
 			break
 		}
@@ -799,43 +816,45 @@ func (h adminHandler) checkHost(r *http.Request) error {
 // sites from issuing requests to our listener. It
 // returns the origin that was obtained from r.
 func (h adminHandler) checkOrigin(r *http.Request) (string, error) {
-	origin := h.getOriginHost(r)
-	if origin == "" {
-		return origin, APIError{
+	originStr, origin := h.getOrigin(r)
+	if origin == nil {
+		return "", APIError{
 			HTTPStatus: http.StatusForbidden,
-			Err:        fmt.Errorf("missing required Origin header"),
+			Err:        fmt.Errorf("required Origin header is missing or invalid"),
 		}
 	}
 	if !h.originAllowed(origin) {
-		return origin, APIError{
+		return "", APIError{
 			HTTPStatus: http.StatusForbidden,
-			Err:        fmt.Errorf("client is not allowed to access from origin %s", origin),
+			Err:        fmt.Errorf("client is not allowed to access from origin '%s'", originStr),
 		}
 	}
-	return origin, nil
+	return origin.String(), nil
 }
 
-func (h adminHandler) getOriginHost(r *http.Request) string {
+func (h adminHandler) getOrigin(r *http.Request) (string, *url.URL) {
 	origin := r.Header.Get("Origin")
 	if origin == "" {
 		origin = r.Header.Get("Referer")
 	}
 	originURL, err := url.Parse(origin)
-	if err == nil && originURL.Host != "" {
-		origin = originURL.Host
+	if err != nil {
+		return origin, nil
 	}
-	return origin
+	originURL.Path = ""
+	originURL.RawPath = ""
+	originURL.Fragment = ""
+	originURL.RawFragment = ""
+	originURL.RawQuery = ""
+	return origin, originURL
 }
 
-func (h adminHandler) originAllowed(origin string) bool {
+func (h adminHandler) originAllowed(origin *url.URL) bool {
 	for _, allowedOrigin := range h.allowedOrigins {
-		originCopy := origin
-		if !strings.Contains(allowedOrigin, "://") {
-			// no scheme specified, so allow both
-			originCopy = strings.TrimPrefix(originCopy, "http://")
-			originCopy = strings.TrimPrefix(originCopy, "https://")
+		if allowedOrigin.Scheme != "" && origin.Scheme != allowedOrigin.Scheme {
+			continue
 		}
-		if originCopy == allowedOrigin {
+		if origin.Host == allowedOrigin.Host {
 			return true
 		}
 	}
@@ -1189,6 +1208,18 @@ func decodeBase64DERCert(certStr string) (*x509.Certificate, error) {
 	return x509.ParseCertificate(derBytes)
 }
 
+type loggableURLArray []*url.URL
+
+func (ua loggableURLArray) MarshalLogArray(enc zapcore.ArrayEncoder) error {
+	if ua == nil {
+		return nil
+	}
+	for _, u := range ua {
+		enc.AppendString(u.String())
+	}
+	return nil
+}
+
 var (
 	// DefaultAdminListen is the address for the local admin
 	// listener, if none is specified at startup.