18529 nomad executes any file in plugins (#18530)

Co-authored-by: James Rasell <jrasell@hashicorp.com>

.changelog/18530.txt

@@ -0,0 +1,3 @@
+```release-note:breaking-change
+agent: Plugins stored within the `plugin_dir` will now only be executed when they have a corresponding `plugin` configuration block. Any plugin found without a corresponding configuration block will be skipped.
+```

helper/pluginutils/loader/init.go

@@ -264,10 +264,15 @@ func (l *PluginLoader) fingerprintPlugins(plugins []os.FileInfo, configs map[str
 	fingerprinted := make(map[PluginID]*pluginInfo, len(plugins))
 	for _, p := range plugins {
 		name := cleanPluginExecutable(p.Name())
+
+		// Use the cleaned plugin name to check whether it is configured by the
+		// operator for use. If it is not, skip loading it and log a message, so
+		// operators can easily see this.
 		c, ok := configs[name]
 		if !ok {
-			// COMPAT(1.7): Skip executing unconfigured plugins in 1.8 or later.
-			l.logger.Warn("plugin not referenced in the agent configuration file, future versions of Nomad will not load this plugin until the agent configuration is updated", "plugin", name)
+			l.logger.Warn("plugin not referenced in the agent configuration file, loading skipped",
+				"plugin", name)
+			continue
 		}
 		info, err := l.fingerprintPlugin(p, c)
 		if err != nil {

helper/pluginutils/loader/loader_test.go

@@ -102,8 +102,9 @@ func TestPluginLoader_External(t *testing.T) {
 	ci.Parallel(t)
 	require := require.New(t)
 
-	// Create two plugins
-	plugins := []string{"mock-device", "mock-device-2"}
+	// Create three plugins. Only two will be referenced within the agent config
+	// meaning the third should not be loaded.
+	plugins := []string{"mock-device", "mock-device-2", "mock-device-3"}
 	pluginVersions := []string{"v0.0.1", "v0.0.2"}
 	h := newHarness(t, plugins)
 
@@ -133,6 +134,8 @@ func TestPluginLoader_External(t *testing.T) {
 	require.NoError(err)
 
 	// Get the catalog and assert we have the two plugins
+	//
+	// Note: mock-device-3 is ignored because it does not have a related config.
 	c := l.Catalog()
 	require.Len(c, 1)
 	require.Contains(c, base.PluginTypeDevice)

website/content/docs/upgrade/upgrade-specific.mdx

@@ -36,6 +36,13 @@ Drivers with the `RemoteTasks` capability will no longer be detached in the even
 the allocation is lost, nor will remote tasks be detached when a node is drained.
 Workloads running as remote tasks should be migrated prior to upgrading.
 
+#### Loading Binaries from `plugin_dir` Without Configuration
+
+Plugins stored within the [`plugin_dir`](/nomad/docs/configuration#plugin_dir)
+will now only be loaded when they have a corresponding
+[`plugin`](/nomad/docs/configuration/plugin) block in the agent configuration
+file.
+
 ## Nomad 1.9.5
 
 #### CNI plugins