bug#34373: Acknowledgement (26.1; Missing range check in rx-submatch-n)

[Andy Moreton <andrewjmoreton@gmail.com>]

On Thu 07 Feb 2019, Mattias Engdegård wrote:

> Patch.
>
> From cc7bbab39595b117f6f2ed2bcf5ea1782060e574 Mon Sep 17 00:00:00 2001
> From: =?UTF-8?q?Mattias=20Engdeg=C3=A5rd?= <mattiase@acm.org>
> Date: Thu, 7 Feb 2019 19:05:06 +0100
> Subject: [PATCH] Check validity of rx submatch-n number
>
> * lisp/emacs-lisp/rx.el (rx-submatch): Type and range check (Bug#34373).
> ---
>  lisp/emacs-lisp/rx.el | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/lisp/emacs-lisp/rx.el b/lisp/emacs-lisp/rx.el
> index 8b4551d0d3..d47beed975 100644
> --- a/lisp/emacs-lisp/rx.el
> +++ b/lisp/emacs-lisp/rx.el
> @@ -705,6 +705,8 @@ FORM is either `(repeat N FORM1)' or `(repeat N M FORMS...)'."
>  (defun rx-submatch-n (form)
>    "Parse and produce code from FORM, which is `(submatch-n N ...)'."
>    (let ((n (nth 1 form)))
> +    (unless (and (integerp n) (> n 0))
> +      (error "rx `submatch-n' argument must be positive"))
>      (concat "\\(?" (number-to-string n) ":"
>  	    (if (= 3 (length form))
>  		;; Only one sub-form.

You could use (natnump n) instead.

    AndyM