security: reject traversal segments before permission checks

chfs-ng/internal/api/server.go

@@ -123,6 +123,16 @@ func writeJSONError(w http.ResponseWriter, status int, message string) {
 	w.WriteHeader(status)
 	_ = json.NewEncoder(w).Encode(map[string]string{"error": message})
 }
+func unsafePath(p string) bool {
+	p = strings.ReplaceAll(p, "\\", "/")
+	for _, part := range strings.Split(p, "/") {
+		if part == ".." {
+			return true
+		}
+	}
+	return false
+}
+
 func qpath(r *http.Request) string {
 	return strings.Trim(strings.ReplaceAll(r.URL.Query().Get("filepath"), "\\", "/"), "/")
 }
@@ -167,6 +177,10 @@ func writeCreated(w http.ResponseWriter) { w.WriteHeader(http.StatusCreated) }
 
 func (s *Server) files(w http.ResponseWriter, r *http.Request) {
 	a := account(r, s)
+	if unsafePath(r.URL.Query().Get("filepath")) {
+		writeJSONError(w, http.StatusBadRequest, "invalid parameter")
+		return
+	}
 	p := qpath(r)
 	m := a.MaskFor(p)
 	if !m.HasRead() {
@@ -213,6 +227,10 @@ func (s *Server) newdir(w http.ResponseWriter, r *http.Request) {
 	_ = r.ParseMultipartForm(16 << 20)
 	_ = r.ParseForm()
 	p := qpath(r)
+	if unsafePath(r.URL.Query().Get("filepath")) || unsafePath(r.FormValue("filepath")) {
+		writeJSONError(w, http.StatusBadRequest, "invalid parameter")
+		return
+	}
 	if p == "" {
 		p = strings.Trim(strings.ReplaceAll(r.FormValue("filepath"), "\\", "/"), "/")
 	}
@@ -536,6 +554,10 @@ func (s *Server) shared(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	p := strings.Trim(strings.TrimPrefix(r.URL.Path, "/chfs/shared/"), "/")
+	if unsafePath(p) {
+		http.NotFound(w, r)
+		return
+	}
 	fi, err := s.Store.Stat(p)
 	if err != nil {
 		http.NotFound(w, r)
@@ -716,6 +738,10 @@ func (s *Server) webdav(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	vp := strings.Trim(strings.TrimPrefix(r.URL.Path, "/webdav"), "/")
+	if unsafePath(vp) {
+		writeJSONError(w, http.StatusBadRequest, "invalid parameter")
+		return
+	}
 	old := r.URL.Path
 	r.URL.Path = "/" + vp
 	defer func() { r.URL.Path = old }()