bug: Dead `elsif` branch in `__sysopen` permission check silently bypasses parent-dir write-permission enforcement

[Koan-Bot]

Problem

In __sysopen, line 3349 returns ENOENT whenever $mock_file->{'contents'} is undef. This means that by the time execution reaches the permission block at line 3357, $mock_file->{'contents'} is always defined — the elsif ($rw =~ /w/) branch at line 3367 (which checks parent-directory write+execute permission before creating a new file) is unreachable dead code. The equivalent path in __open (line 2827) does reach its elsif and correctly enforces the parent-dir check.

Why This Matters

With set_user() active, sysopen($fh, '/protected/new', O_WRONLY|O_CREAT) will create a file in a restricted directory without error, while open($fh, '>', '/protected/new') correctly returns EACCES. This is a permissions-enforcement inconsistency that could cause tests to pass incorrectly.

Suggested Fix

Move the parent-dir permission check to before the O_CREAT initialization block (lines 3312-3313), or restructure with a flag: save my $is_new = !defined $mock_file->{'contents'} before O_CREAT sets contents to '', then test $is_new in the elsif at line 3367. Example:

my $is_new = !defined $mock_file->{'contents'};
# ... O_CREAT / O_TRUNC logic ...
if ( defined $_mock_uid ) {
    if ( !$is_new ) {
        # existing file — check file perms
    } elsif ( $rw =~ /w/ ) {
        # new file — check parent dir perms
    }
}

Details

Severity	🟠 High
Category	robustness
Location	lib/Test/MockFile.pm:3349-3374
Effort	⚡ Quick fix

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🤖 Created by Kōan from audit session