Merge 2df018666f13470b75d6390dae0963ec715c6605 into d75fcd4c9ab260e5225de590f1f0f8c0e0e12d11

context.go

@@ -716,6 +716,10 @@ func (c *Context) MultipartForm() (*multipart.Form, error) {
 }
 
 // SaveUploadedFile uploads the form file to specific dst.
+// An optional perm argument allows specifying the permission bits for any
+// newly created directories. If not provided, the default is 0750.
+// Note: permissions are only applied to directories created by this call;
+// pre-existing directories (e.g. /tmp) are not modified.
 func (c *Context) SaveUploadedFile(file *multipart.FileHeader, dst string, perm ...fs.FileMode) error {
 	src, err := file.Open()
 	if err != nil {
@@ -728,11 +732,20 @@ func (c *Context) SaveUploadedFile(file *multipart.FileHeader, dst string, perm
 		mode = perm[0]
 	}
 	dir := filepath.Dir(dst)
+	// Check if the directory already exists before calling MkdirAll so we
+	// know whether to apply chmod. We must not chmod pre-existing directories
+	// (e.g. /tmp) because the process may not own them.
+	_, statErr := os.Stat(dir)
 	if err = os.MkdirAll(dir, mode); err != nil {
 		return err
 	}
-	if err = os.Chmod(dir, mode); err != nil {
-		return err
+	// Only apply chmod when the directory was freshly created by MkdirAll.
+	// If the directory already existed, os.Stat returned nil, so we skip
+	// the chmod to avoid "operation not permitted" on unowned directories.
+	if errors.Is(statErr, os.ErrNotExist) {
+		if err = os.Chmod(dir, mode); err != nil {
+			return err
+		}
 	}
 
 	out, err := os.Create(dst)

context_test.go

@@ -275,6 +275,40 @@ func TestSaveUploadedFileWithPermissionFailed(t *testing.T) {
 	require.Error(t, c.SaveUploadedFile(f, "test/permission_test", mode))
 }
 
+// TestSaveUploadedFileToExistingDir is a regression test for issue #4622.
+// SaveUploadedFile must not call os.Chmod on a directory that already exists,
+// because the process may not own it (e.g. /tmp on Linux/macOS).
+func TestSaveUploadedFileToExistingDir(t *testing.T) {
+	buf := new(bytes.Buffer)
+	mw := multipart.NewWriter(buf)
+	w, err := mw.CreateFormFile("file", "existing_dir_test")
+	require.NoError(t, err)
+	_, err = w.Write([]byte("existing_dir_test"))
+	require.NoError(t, err)
+	mw.Close()
+
+	c, _ := CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest(http.MethodPost, "/", buf)
+	c.Request.Header.Set("Content-Type", mw.FormDataContentType())
+	f, err := c.FormFile("file")
+	require.NoError(t, err)
+
+	// Use os.TempDir() which is guaranteed to already exist and may not be
+	// owned by the current process — this is exactly the scenario from #4622.
+	dst := filepath.Join(os.TempDir(), "gin_save_uploaded_regression_test.txt")
+	t.Cleanup(func() {
+		_ = os.Remove(dst)
+	})
+
+	// Must not fail with "chmod ...: operation not permitted"
+	require.NoError(t, c.SaveUploadedFile(f, dst))
+
+	// Verify the file was actually written with correct content
+	content, err := os.ReadFile(dst)
+	require.NoError(t, err)
+	assert.Equal(t, "existing_dir_test", string(content))
+}
+
 func TestContextReset(t *testing.T) {
 	router := New()
 	c := router.allocateContext(0)