security: reject WebDAV virtual-root mutation

chfs-ng/internal/api/server.go

@@ -981,6 +981,9 @@ func (f *webdavStorageFS) Create(ctx context.Context, name string, body io.ReadC
 	if err != nil {
 		return nil, false, err
 	}
+	if isVirtualStorageRoot(f.store, p) {
+		return nil, false, virtualRootMutationError()
+	}
 	_, statErr := f.store.Stat(p)
 	if statErr != nil && !os.IsNotExist(statErr) {
 		return nil, false, statErr
@@ -1002,13 +1005,26 @@ func (f *webdavStorageFS) Create(ctx context.Context, name string, body io.ReadC
 	return fi, true, err
 }
 
+func isVirtualStorageRoot(store storage.Storage, p string) bool {
+	m, ok := store.(storage.Multi)
+	if !ok {
+		return false
+	}
+	_, rel, found := m.FindRoot(p)
+	return found && rel == ""
+}
+
+func virtualRootMutationError() error {
+	return webdav.NewHTTPError(http.StatusForbidden, fmt.Errorf("cannot modify virtual root"))
+}
+
 func (f *webdavStorageFS) RemoveAll(ctx context.Context, name string, opts *webdav.RemoveAllOptions) error {
 	p, err := davSafePath(name)
 	if err != nil {
 		return err
 	}
-	if p == "" {
-		return fmt.Errorf("cannot remove storage root")
+	if p == "" || isVirtualStorageRoot(f.store, p) {
+		return virtualRootMutationError()
 	}
 	if _, err := f.store.Stat(p); err != nil {
 		if os.IsNotExist(err) {
@@ -1038,8 +1054,8 @@ func (f *webdavStorageFS) Mkdir(ctx context.Context, name string) error {
 	if err != nil {
 		return err
 	}
-	if p == "" {
-		return fmt.Errorf("cannot create storage root")
+	if p == "" || isVirtualStorageRoot(f.store, p) {
+		return virtualRootMutationError()
 	}
 	if _, err := f.store.Stat(p); err == nil {
 		return webdav.NewHTTPError(http.StatusMethodNotAllowed, fmt.Errorf("resource already exists"))
@@ -1061,6 +1077,9 @@ func (f *webdavStorageFS) Copy(ctx context.Context, name, dest string, opts *web
 	if sameOrDescendantPath(src, dst) {
 		return false, webdav.NewHTTPError(http.StatusConflict, fmt.Errorf("destination is inside source"))
 	}
+	if isVirtualStorageRoot(f.store, src) || isVirtualStorageRoot(f.store, dst) {
+		return false, virtualRootMutationError()
+	}
 	_, dstErr := f.store.Stat(dst)
 	dstExists := dstErr == nil
 	if dstErr != nil && !os.IsNotExist(dstErr) {
@@ -1130,6 +1149,9 @@ func (f *webdavStorageFS) Move(ctx context.Context, name, dest string, opts *web
 	if sameOrDescendantPath(src, dst) {
 		return false, webdav.NewHTTPError(http.StatusConflict, fmt.Errorf("destination is inside source"))
 	}
+	if isVirtualStorageRoot(f.store, src) || isVirtualStorageRoot(f.store, dst) {
+		return false, virtualRootMutationError()
+	}
 	if _, err := f.store.Stat(dst); err == nil {
 		// CHFS v4 MOVE does not overwrite an existing destination, even when
 		// Overwrite is omitted/T and the caller has delete permission.