I would sanitize everything anyway. Although the directories are under your control, think about these:

• What if in the future you add the possibility for users to add their own directories, and then forget to go back and change this code to check them before using them?
• What if through some other means someone manages to add a directory with a weird name?

I'm not sure if data read from readdir() is considered tainted or not, but you should check everything. Come up with a regex that describes all the valid directory names that you expect to have, and check against that. Something like this:

foreach (@dir) {
  s/^(\w+)$/$1/ || do { generate some error message, or 
                        skip this directory };
}
[download]

Which will allow directory names with any alphanumeric characters plus the underscore. Remember not to check for invalid characters (you could miss some), but to only allow valid ones (like the code above).

A similar untainting should probably be applied to user-supplied data, plus checking that it is in the list of valid directories.

--ZZamboni

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