Re: [PATCH] Allow globbing with unreadable parent directories

[Bart Schaefer <schaefer@brasslantern.com>]

On Wed, Jan 13, 2021 at 4:28 PM Devin Hussey <husseydevin@gmail.com> wrote:
>
> On Wed, Jan 13, 2021, 5:28 PM Bart Schaefer <schaefer@brasslantern.com> wrote:
>>
>> On Tue, Jan 12, 2021 at 7:04 PM Devin Hussey <husseydevin@gmail.com> wrote:
>> >
>> > POSIX specifies that when globbing, parent directories only have to be
>> > searchable, not readable.
>>
>> Lack of search permission only means that you can't tell what kind of
>> file "somefile" is (you can't read its inode data, e.g., stat() it),
>> not that you can't see the name itself.
>
> This matches the behavior of the "pure" globber, POSIX, and literally every other shell.

I tried the same test cases with "bash" and it behaved like
(unpatched) zsh.  Again, can you show me a counter-example?

> Case insensitivity should not change the output due to file permissions.

If that were a property of the filesystem, as for example on MacOS,
then I agree with you.

It's less clear when the filesystem is case-sensitive.  Why should
(#i)file not be the same as [Ff][Ii][Ll][Ee] ?

> opendir(fn) will also fail if the "folder" is a file.

Sure, but so might access(R_OK) ... and access(X_OK) might succeed on a file.

>> 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.
>
> opendir() would fail if either R_OK or X_OK was false, causing unreadable folders to be a false negative.

I don't think that's true.  opendir() is fine with only R_OK.  Again,
try "ls" on a directory having mode 444.

What you cannot do is "ls -l parent/child" when parent is not searchable.

The actual problem is that PAT_PURES is never true when NO_CASE_GLOB
is set.  That means scanner() always passes through the branch that
attempts zreaddir()+pattry(), which fails when there is an unreadable
directory.  I'm not immediately sure how to fix that without
introducing a bug/vulnerability where a filename could be constructed
such that it literally matches the internal representation of a glob
pattern.