security: harden recursive file operations

chfs-ng/internal/storage/storage.go

@@ -97,10 +97,36 @@ func (s Local) Create(path string) (*os.File, error) {
 }
 func (s Local) Remove(path string) error {
 	p, e := s.real(path)
-	if e != nil {
+	if e == nil {
+		return os.RemoveAll(p)
+	}
+	// A final symlink that points outside the root is still safe to delete:
+	// remove the link itself, but never follow it to its target. Validate its
+	// parent through real() so nested symlink escapes remain rejected.
+	clean := strings.TrimPrefix(filepath.Clean("/"+path), string(filepath.Separator))
+	if clean == "" {
 		return e
 	}
-	return os.RemoveAll(p)
+	parent := filepath.ToSlash(filepath.Dir(clean))
+	if parent == "." {
+		parent = ""
+	}
+	if _, parentErr := s.real(parent); parentErr != nil {
+		return e
+	}
+	root, rootErr := filepath.Abs(s.Root)
+	if rootErr != nil {
+		return e
+	}
+	root, rootErr = filepath.EvalSymlinks(root)
+	if rootErr != nil {
+		return e
+	}
+	candidate := filepath.Join(root, filepath.FromSlash(clean))
+	if info, lstatErr := os.Lstat(candidate); lstatErr == nil && info.Mode()&os.ModeSymlink != 0 {
+		return os.Remove(candidate)
+	}
+	return e
 }
 
 func (s Local) Trash(path string) error {

chfs-ng/internal/storage/storage_test.go

@@ -7,6 +7,29 @@ import (
 	"time"
 )
 
+func TestLocalRemoveSymlinkDoesNotDeleteTarget(t *testing.T) {
+	root := t.TempDir()
+	outside := t.TempDir()
+	target := filepath.Join(outside, "secret.txt")
+	if err := os.WriteFile(target, []byte("keep"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	link := filepath.Join(root, "link")
+	if err := os.Symlink(target, link); err != nil {
+		t.Skipf("symlink unavailable: %v", err)
+	}
+	store := Local{Root: root}
+	if err := store.Remove("link"); err != nil {
+		t.Fatalf("remove symlink: %v", err)
+	}
+	if _, err := os.Stat(target); err != nil {
+		t.Fatalf("symlink removal must not delete target: %v", err)
+	}
+	if _, err := os.Lstat(link); !os.IsNotExist(err) {
+		t.Fatalf("symlink should be removed, got %v", err)
+	}
+}
+
 func TestLocalRejectsSymlinkEscapeAndAllowsNestedCreate(t *testing.T) {
 	root := t.TempDir()
 	outside := t.TempDir()