Treat PRs with agit flow as fork PRs when triggering actions. (#23884)

There is no fork concept in agit flow, anyone with read permission can
push `refs/for/<target-branch>/<topic-branch>` to the repo. So we should
treat it as a fork pull request because it may be from an untrusted
user.

models/actions/run.go

@@ -36,7 +36,7 @@ type ActionRun struct {
 	TriggerUser       *user_model.User       `xorm:"-"`
 	Ref               string
 	CommitSHA         string
-	IsForkPullRequest bool
+	IsForkPullRequest bool  // If this is triggered by a PR from a forked repository or an untrusted user, we need to check if it is approved and limit permissions when running the workflow.
 	NeedApproval      bool  // may need approval if it's a fork pull request
 	ApprovedBy        int64 `xorm:"index"` // who approved
 	Event             webhook_module.HookEventType

services/actions/notifier_helper.go

@@ -152,6 +152,21 @@ func notify(ctx context.Context, input *notifyInput) error {
 		return fmt.Errorf("json.Marshal: %w", err)
 	}
 
+	isForkPullRequest := false
+	if pr := input.PullRequest; pr != nil {
+		switch pr.Flow {
+		case issues_model.PullRequestFlowGithub:
+			isForkPullRequest = pr.IsFromFork()
+		case issues_model.PullRequestFlowAGit:
+			// There is no fork concept in agit flow, anyone with read permission can push refs/for/<target-branch>/<topic-branch> to the repo.
+			// So we can treat it as a fork pull request because it may be from an untrusted user
+			isForkPullRequest = true
+		default:
+			// unknown flow, assume it's a fork pull request to be safe
+			isForkPullRequest = true
+		}
+	}
+
 	for id, content := range workflows {
 		run := &actions_model.ActionRun{
 			Title:             strings.SplitN(commit.CommitMessage, "\n", 2)[0],
@@ -161,7 +176,7 @@ func notify(ctx context.Context, input *notifyInput) error {
 			TriggerUserID:     input.Doer.ID,
 			Ref:               ref,
 			CommitSHA:         commit.ID.String(),
-			IsForkPullRequest: input.PullRequest != nil && input.PullRequest.IsFromFork(),
+			IsForkPullRequest: isForkPullRequest,
 			Event:             input.Event,
 			EventPayload:      string(p),
 			Status:            actions_model.StatusWaiting,