Re: [PATCH] Allow globbing with unreadable parent directories

[Devin Hussey <husseydevin@gmail.com>]

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On Wed, Jan 13, 2021, 8:33 PM Lawrence Velázquez <vq@larryv.me> wrote:

> > On Jan 13, 2021, at 7:27 PM, Devin Hussey <husseydevin@gmail.com> wrote:
> >
> >> On Wed, Jan 13, 2021, 5:28 PM Bart Schaefer <schaefer@brasslantern.com>
> wrote:
> >>
> >> As far as I can tell, the patch
> >> would only cause globbing to fail in more cases, not succeed where it
> >> previously did not.
> >
> > No, that is definitely not the case.
>
> But your patch *does* cause globbing to fail in cases for which it
> currently doesn't.
>
>         % mkdir -p notsearchable/{dir,DIR}
>         % touch notsearchable/{dir,DIR}/file
>         % chmod 600 notsearchable
>         % zsh -fc 'echo notsearchable/*'
>         notsearchable/DIR notsearchable/dir
>         % ./zsh-patched -fc 'echo notsearchable/*'
>         zsh:1: no matches found: notsearchable/*
>

Huh. Yeah, that is a bug.

I don't yet understand enough of the logic.

> opendir() would fail if either R_OK or X_OK was false, causing unreadable
> folders to be a false negative.
> >
> > This is allowing certain combinations where opendir() would fail.
>
> If I'm understanding your intention correctly, you would like
> "literal" segments (e.g., lacking special characters) of
> case-insensitive glob patterns to match literally if the "parent"
> lacks read permissions. This doesn't seem to work, though. Am I
> missing something?
>

That is correct.

To reiterate the problem:

 - Case-sensitive (and POSIX) globs seemingly only fail if the parent
directory is unsearchable or if the target directory is unreadable, as it
only opens the globbed directory.

 - The case-insensitive ("impure") glob will fail if ANY parent is
unreadable or unsearchable. This is because unlike the normal glob, the
impure glob will try to recursively opendir() from "/".

 - If I ignore EACCES entirely like in my first patch, case-insensitive
globs would succeed if the parent is unsearchable, causing the opposite bug
where case-sensitive globs fail.

 - The current patch does not handle the target directory being readable
but not searchable.

I admit that I know very little about the Zsh source tree, so I have tunnel
vision when it comes to the program logic. It is likely I who is missing
something obvious.

The only reason that I found the cause of this bug was via strace.

        % mkdir -p notreadable/dir
>         % touch notreadable/dir/file
>         % chmod 300 notreadable
>         % zsh -f +o CASE_GLOB -c 'echo notreadable/dir/*'
>         zsh:1: no matches found: notreadable/dir/*
>         % ./zsh-patched -f +o CASE_GLOB -c 'echo notreadable/dir/*'
>         zsh:1: no matches found: notreadable/dir/*


I didn't do anything that would directly affect CASE_GLOB, as CASE_GLOB
uses the "pure" codepath. It is expected that the behavior would not change.

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