Fix host cleanup, volume allowlist, cache upload, and action host edge cases (#970)

## Summary
- prevent host-mode execution from deleting caller-owned workdirs
- harden `valid_volumes` checks against `..` and symlink escapes
- return immediately after artifact cache upload write failures
- default implicit remote action clone hosts to `GitHubInstance`/`github.com`

Authored with assistance from OpenAI Codex GPT-5.

---------

Co-authored-by: silverwind <me@silverwind.io>
Reviewed-on: https://gitea.com/gitea/runner/pulls/970
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>

act/runner/run_context.go

@@ -220,12 +220,12 @@ func (rc *RunContext) startHostEnvironment() common.Executor {
 		}
 		toolCache := filepath.Join(cacheDir, "tool_cache")
 		rc.JobContainer = &container.HostEnvironment{
-			Path:        path,
-			TmpDir:      runnerTmp,
-			ToolCache:   toolCache,
-			Workdir:     rc.Config.Workdir,
-			BindWorkdir: rc.Config.BindWorkdir,
-			ActPath:     actPath,
+			Path:         path,
+			TmpDir:       runnerTmp,
+			ToolCache:    toolCache,
+			Workdir:      rc.Config.Workdir,
+			CleanWorkdir: rc.Config.CleanWorkdir,
+			ActPath:      actPath,
 			CleanUp: func() {
 				os.RemoveAll(miscpath)
 			},

act/runner/runner.go

@@ -73,6 +73,7 @@ type Config struct {
 	EventJSON             string                       // the content of JSON file to use for event.json in containers, overrides EventPath
 	ContainerNamePrefix   string                       // the prefix of container name
 	ContainerMaxLifetime  time.Duration                // the max lifetime of job containers
+	CleanWorkdir          bool                         // remove host executor workdir on teardown
 	DefaultActionInstance string                       // the default actions web site
 	PlatformPicker        func(labels []string) string // platform picker, it will take precedence over Platforms if isn't nil
 	JobLoggerLevel        *log.Level                   // the level of job logger
@@ -91,6 +92,17 @@ func (c Config) GetToken() string {
 	return token
 }
 
+// DefaultActionURL returns the host used for implicit remote actions.
+func (c Config) DefaultActionURL() string {
+	if c.DefaultActionInstance != "" {
+		return c.DefaultActionInstance
+	}
+	if c.GitHubInstance != "" {
+		return c.GitHubInstance
+	}
+	return "github.com"
+}
+
 type caller struct {
 	runContext *RunContext
 

act/runner/step_action_remote.go

@@ -113,9 +113,10 @@ func (sar *stepActionRemote) prepareActionExecutor() common.Executor {
 		}
 
 		actionDir := fmt.Sprintf("%s/%s", sar.RunContext.ActionCacheDir(), sar.Step.UsesHash())
-		token := getGitCloneToken(sar.getRunContext().Config, sar.remoteAction.CloneURL(sar.RunContext.Config.DefaultActionInstance))
+		defaultActionURL := sar.RunContext.Config.DefaultActionURL()
+		token := getGitCloneToken(sar.getRunContext().Config, sar.remoteAction.CloneURL(defaultActionURL))
 		gitClone := stepActionRemoteNewCloneExecutor(git.NewGitCloneExecutorInput{
-			URL:         sar.remoteAction.CloneURL(sar.RunContext.Config.DefaultActionInstance),
+			URL:         sar.remoteAction.CloneURL(defaultActionURL),
 			Ref:         sar.remoteAction.Ref,
 			Dir:         actionDir,
 			Token:       token,
@@ -274,7 +275,7 @@ func (sar *stepActionRemote) cloneSkipTLS() bool {
 	if sar.remoteAction.URL == "" {
 		// Empty URL means the default action instance should be used
 		// Return true if the URL of the Gitea instance is the same as the URL of the default action instance
-		return sar.RunContext.Config.DefaultActionInstance == sar.RunContext.Config.GitHubInstance
+		return sar.RunContext.Config.DefaultActionURL() == sar.RunContext.Config.GitHubInstance
 	}
 	// Return true if the URL of the remote action is the same as the URL of the Gitea instance
 	return sar.remoteAction.URL == sar.RunContext.Config.GitHubInstance

act/runner/step_action_remote_test.go

@@ -20,6 +20,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/mock"
+	"github.com/stretchr/testify/require"
 	"go.yaml.in/yaml/v4"
 )
 
@@ -434,6 +435,57 @@ func TestStepActionRemotePreThroughActionToken(t *testing.T) {
 	}
 }
 
+func TestStepActionRemoteUsesGitHubInstanceWhenDefaultActionInstanceEmpty(t *testing.T) {
+	ctx := context.Background()
+
+	var actualURL string
+	sarm := &stepActionRemoteMocks{}
+
+	origStepAtionRemoteNewCloneExecutor := stepActionRemoteNewCloneExecutor
+	stepActionRemoteNewCloneExecutor = func(input git.NewGitCloneExecutorInput) common.Executor {
+		return func(ctx context.Context) error {
+			actualURL = input.URL
+			return nil
+		}
+	}
+	defer func() {
+		stepActionRemoteNewCloneExecutor = origStepAtionRemoteNewCloneExecutor
+	}()
+
+	sar := &stepActionRemote{
+		Step: &model.Step{
+			Uses: "actions/setup-go@v4",
+		},
+		RunContext: &RunContext{
+			Config: &Config{
+				GitHubInstance:        "gitea.example",
+				DefaultActionInstance: "",
+				ActionCacheDir:        t.TempDir(),
+			},
+			Run: &model.Run{
+				JobID: "1",
+				Workflow: &model.Workflow{
+					Jobs: map[string]*model.Job{
+						"1": {},
+					},
+				},
+			},
+		},
+		readAction: sarm.readAction,
+	}
+
+	suffixMatcher := func(suffix string) any {
+		return mock.MatchedBy(func(actionDir string) bool {
+			return strings.HasSuffix(actionDir, suffix)
+		})
+	}
+	sarm.On("readAction", sar.Step, suffixMatcher(sar.Step.UsesHash()), "", mock.Anything, mock.Anything).Return(&model.Action{}, nil)
+
+	require.NoError(t, sar.prepareActionExecutor()(ctx))
+	assert.Equal(t, "https://gitea.example/actions/setup-go", actualURL)
+	sarm.AssertExpectations(t)
+}
+
 func TestStepActionRemotePost(t *testing.T) {
 	table := []struct {
 		name               string