getchmod() can cause Fatal error

[apermo]

/wp-admin/includes/class-wp-filesystem-ftpsockets.php:326: Trying to access array offset on value of type bool

In both classes WP_Filesystem_FTPext and WP_Filesystem_ftpsockets

The function getchmod() looks like this:

<?php
public function getchmod( $file ) {
        $dir = $this->dirlist( $file );

        return $dir[ $file ]['permsn'];
}

and dirlist() can in both cases return false under certain conditions.

While it is rare and I could not yet figure out how to reproduce it, this will cause a fatal error.

I suggest to add a simple condition that will check if $dir is an array, and return either an empty string or null if it's not.

This will fix the error, without delivering wrong information.

<?php
public function getchmod( $file ) {
        $dir = $this->dirlist( $file );

        if ( ! empty( $dir[ $file ]['permsn'] ) ) {
                return $dir[ $file ]['permsn'];
        }

        return '';
}

Props to @malt3 for running into it.

Co-authored-by: @zaphir
Ref: https://core.trac.wordpress.org/ticket/63474#ticket

Fixes 63474 in the way suggested in the ticket.

Trac ticket: https://core.trac.wordpress.org/ticket/63474#ticket