From 05bd06e405d34b53eed1c0812d846d28038bb14a Mon Sep 17 00:00:00 2001
From: "xinjun.jiang" <xinjun.jiang@daocloud.io>
Date: Tue, 22 Sep 2026 15:57:24 +0800
Subject: [PATCH] fix: handle null Docker runtimes

A JSON null runtimes entry decodes to a nil interface. Adding, removing,
or looking up a runtime currently asserts that value to a map and panics.
Treat a null runtimes entry like an absent entry before the assertion.

Cover all three operations using a configuration loaded from a file and
verify unrelated settings survive saving the updated configuration.

Signed-off-by: xinjun.jiang <xinjun.jiang@daocloud.io>
---
 pkg/config/engine/docker/docker.go      |  6 ++---
 pkg/config/engine/docker/docker_test.go | 33 +++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/pkg/config/engine/docker/docker.go b/pkg/config/engine/docker/docker.go
index fb6f502f5..696a3ae9f 100644
--- a/pkg/config/engine/docker/docker.go
+++ b/pkg/config/engine/docker/docker.go
@@ -74,7 +74,7 @@ func (c *Config) AddRuntime(name string, path string, setAsDefault bool) error {
 
 	// Read the existing runtimes
 	runtimes := make(map[string]any)
-	if _, exists := config["runtimes"]; exists {
+	if config["runtimes"] != nil {
 		runtimes = config["runtimes"].(map[string]any)
 	}
 
@@ -135,7 +135,7 @@ func (c *Config) RemoveRuntime(name string) error {
 		}
 	}
 
-	if _, exists := config["runtimes"]; exists {
+	if config["runtimes"] != nil {
 		runtimes := config["runtimes"].(map[string]any)
 
 		delete(runtimes, name)
@@ -203,7 +203,7 @@ func (c *Config) GetRuntimeConfig(name string) (engine.RuntimeConfig, error) {
 	cfg := *c
 
 	var runtimes map[string]any
-	if _, ok := cfg["runtimes"]; ok {
+	if cfg["runtimes"] != nil {
 		runtimes = cfg["runtimes"].(map[string]any)
 		if r, ok := runtimes[name]; ok {
 			dr := dockerRuntime(r.(map[string]any))
diff --git a/pkg/config/engine/docker/docker_test.go b/pkg/config/engine/docker/docker_test.go
index b5ea75c03..ce9dc1497 100644
--- a/pkg/config/engine/docker/docker_test.go
+++ b/pkg/config/engine/docker/docker_test.go
@@ -250,6 +250,39 @@ func TestGetRuntimeConfig(t *testing.T) {
 	}
 }
 
+func TestNullRuntimesFromFile(t *testing.T) {
+	for _, action := range []string{"add", "remove", "get"} {
+		t.Run(action, func(t *testing.T) {
+			configPath := filepath.Join(t.TempDir(), "daemon.json")
+			require.NoError(t, os.WriteFile(configPath, []byte(`{"runtimes":null,"log-driver":"json-file"}`), 0600))
+			config, err := New(WithPath(configPath))
+			require.NoError(t, err)
+
+			switch action {
+			case "add":
+				require.NoError(t, config.AddRuntime("nvidia", "/usr/bin/nvidia-container-runtime", false))
+				runtime, err := config.GetRuntimeConfig("nvidia")
+				require.NoError(t, err)
+				require.Equal(t, "/usr/bin/nvidia-container-runtime", runtime.GetBinaryPath())
+			case "remove":
+				require.NoError(t, config.RemoveRuntime("nvidia"))
+			case "get":
+				runtime, err := config.GetRuntimeConfig("nvidia")
+				require.NoError(t, err)
+				require.Empty(t, runtime.GetBinaryPath())
+			}
+
+			_, err = config.Save(configPath)
+			require.NoError(t, err)
+			contents, err := os.ReadFile(configPath)
+			require.NoError(t, err)
+			var saved map[string]any
+			require.NoError(t, json.Unmarshal(contents, &saved))
+			require.Equal(t, "json-file", saved["log-driver"])
+		})
+	}
+}
+
 func TestEnableCDIPreservesFeaturesFromFile(t *testing.T) {
 	tests := []struct {
 		name     string