GNU bug report logs - #49723
28.0.50; Test in coding.c for NUL bytes in filenames is not reliable

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From: Federico Tedin <federicotedin <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: phst <at> google.com, 49723 <at> debbugs.gnu.org
Subject: bug#49723: 28.0.50; Test in coding.c for NUL bytes in filenames is not reliable
Date: Wed, 15 Sep 2021 00:17:33 +0200

[Message part 1 (text/plain, inline)]

Ok! Here's my first try at this. I ended up skipping the check on
DEFAULT-DIRECTORY since as you mentioned, its value is used with
expand-file-name itself. In the other case, if default-directory is
picked up, then I checked the value of that variable.

[expand-file-name.patch (text/x-diff, attachment)]

[Message part 3 (text/plain, inline)]

Eli Zaretskii <eliz <at> gnu.org> writes:

>> From: Federico Tedin <federicotedin <at> gmail.com>
>> Cc: 49723 <at> debbugs.gnu.org,  Philipp Stephani <phst <at> google.com>
>> Date: Tue, 14 Sep 2021 21:01:16 +0200
>> 
>> I'm interested in looking into this one since I want to learn more about
>> the C side of the codebase. However, I wasn't able to find a call to
>> expand-file-name in encode_file_name or encode_file_name_1. I did find
>> the null byte check though (CHECK_TYPE + memchr). Maybe I am missing
>> something out.
>
> My description was inaccurate: the expand-file-name call usually
> precedes the call to ENCODE_FILE, it is not part of encode_file_name.
>
>> I assume that a similar check on expand-file-name should be applied to
>> both input arguments, NAME and DEFAULT-DIRECTORY?
>
> I don't think we need that because expand-file-name calls itself on
> DEFAULT-DIRECTORY internally.  But we may need to perform the check on
> default-directory, if we use it inside expand-file-name.

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