Reject special files before preparing inputs

internal/stage/prepare.go

@@ -635,6 +635,13 @@ func requireRegularReadableFile(path string, label string) error {
 	if strings.TrimSpace(path) == "" {
 		return fmt.Errorf("%s path is required", label)
 	}
+	declared, err := os.Lstat(path)
+	if err != nil {
+		return fmt.Errorf("inspect %s %q: %w", label, path, err)
+	}
+	if declared.Mode()&os.ModeSymlink != 0 || !declared.Mode().IsRegular() {
+		return fmt.Errorf("%s %q is not a regular file without symlinks", label, path)
+	}
 	file, err := os.Open(path)
 	if err != nil {
 		return fmt.Errorf("open %s %q: %w", label, path, err)
@@ -644,8 +651,13 @@ func requireRegularReadableFile(path string, label string) error {
 	if statErr != nil {
 		return fmt.Errorf("stat %s %q: %w", label, path, statErr)
 	}
-	if !info.Mode().IsRegular() {
-		return fmt.Errorf("%s %q is not a regular file", label, path)
+	current, currentErr := os.Lstat(path)
+	if currentErr != nil {
+		return fmt.Errorf("reinspect %s %q: %w", label, path, currentErr)
+	}
+	if !info.Mode().IsRegular() || current.Mode()&os.ModeSymlink != 0 || !current.Mode().IsRegular() ||
+		!os.SameFile(info, declared) || !os.SameFile(info, current) {
+		return fmt.Errorf("%s %q changed while being opened", label, path)
 	}
 	if closeErr != nil {
 		return fmt.Errorf("close %s %q: %w", label, path, closeErr)

internal/stage/prepare_fifo_test.go

@@ -0,0 +1,45 @@
+//go:build unix
+
+package stage
+
+import (
+	"context"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/config"
+	"golang.org/x/sys/unix"
+)
+
+func TestPrepareStageRejectsSpellCatalogFIFOWithoutBlocking(t *testing.T) {
+	env, m := setupPrepareEnv(t)
+	root := filepath.Dir(env.Config.SessionPath)
+	writeFile(t, filepath.Join(root, "audio", "a.flac"), "audio")
+	env.Config.Session.Inputs.AudioFiles = []string{"./audio/a.flac"}
+
+	sourcePath := filepath.Join(root, "spells.fifo")
+	if err := unix.Mkfifo(sourcePath, 0o644); err != nil {
+		t.Fatalf("Mkfifo() error = %v", err)
+	}
+	env.Config.StableInputs.SpellCatalogFile = config.ResolvedInputFile{
+		Path:       "./spells.fifo",
+		ConfigPath: env.Config.CampaignPath,
+		Source:     "campaign_config",
+	}
+
+	done := make(chan error, 1)
+	go func() {
+		_, err := (prepareStage{}).Run(context.Background(), env, m)
+		done <- err
+	}()
+	select {
+	case err := <-done:
+		if err == nil || !strings.Contains(err.Error(), "not a regular file") {
+			t.Fatalf("prepare.Run() error = %v, want regular-file rejection", err)
+		}
+	case <-time.After(time.Second):
+		t.Fatal("prepare.Run() blocked while inspecting a FIFO spell catalog")
+	}
+}