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

From: Robert Pluim <[email-masked]>
Date: Tue, 19 Feb 2019 18:37:26 +0100

Eli Zaretskii <[email-masked]> writes:

>> From: Robert Pluim <[email-masked]>
>> Date: Tue, 19 Feb 2019 11:06:37 +0100
>> Cc: [email-masked], Nicholas Drozd <[email-masked]>
>> 
>> Glenn Morris <[email-masked]> 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.
>

Since this is all due to a C-ism in the handling of content, Iʼd vote
for "\0", although this is inside Emacs, so perhaps "^@" is best.

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

I really donʼt think this is something that needs to be configurable.

Robert