bug#34469: 26.1; EWW stops renderring web page on null byte

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Date: Tue, 19 Feb 2019 11:06:37 +0100
> Cc: 34469@debbugs.gnu.org, Nicholas Drozd <nicholasdrozd@gmail.com>
> 
> Glenn Morris <rgm@gnu.org> writes:
> 
> > Perhaps eww-display-html should replace null bytes (with whatever the
> > html standard says is appropriate) before calling
> > libxml-parse-html-region. It already replaces CRLF.
> 
> Chrome at least just strips the null byte completely.
> 
> There is apparently a class of attacks that uses the null character
> for nefarious purposes, so how about something like this:
> 
> diff --git a/lisp/net/eww.el b/lisp/net/eww.el
> index 1cc4557ce1..9b57bc43e4 100644
> --- a/lisp/net/eww.el
> +++ b/lisp/net/eww.el
> @@ -448,8 +448,8 @@ eww-display-html
>                   (decode-coding-region (point) (point-max) encode)
>                 (coding-system-error nil))
>                  (save-excursion
> -                  ;; Remove CRLF before parsing.
> -                  (while (re-search-forward "\r$" nil t)
> +                  ;; Remove CRLF and NULL before parsing.
> +                  (while (re-search-forward "\r$\\|\000" nil t)
>                      (replace-match "" t t)))

It is un-Emacsy, IMO, to remove content without a trace.  (CR is
different: we simply convert text to Unix LF-only EOL format.)  So I'd
suggest to replace with "^@" or "\000" or "NUL" or something to that
effect.  Even U+FFFD would be better than removing.

(We could get fancy and have a defcustom for those who do want the
null bytes removed.)

Thanks.