full-disclosure - Re: Possibility to exploit bash "*" processing

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Date: Wed, 21 Sep 2011 12:55:33 -0400
From: Valdis.Kletnieks@...edu
To: Dan Carpenter <error27@...il.com>
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: Possibility to exploit bash "*" processing

On Wed, 21 Sep 2011 16:01:24 +0300, Dan Carpenter said:
> Seems like a good time to promote David Wheeler's filename proposal:
> http://www.dwheeler.com/essays/fixing-unix-linux-filenames.html

Unfortunately, David Wheeler's proposal has some implementation issues:

1. Forbid/escape ASCII control characters (bytes 1-31 and 127) in filenames,
including newline, escape, and tab.

3. Forbid/escape filenames that aren't a valid UTF-8 encoding.

The problem is that the UTF-8 codespace consists *mostly* of multibyte
characters, wherein at least one of the bytes, when considered by itself, is an
ASCII control character.  So if you restrict filenames to valid UTF-8, you
*still* lose if the filename is parsed by a non-UTF-8-aware program.  And if
you eliminate those valid UTF-8 names that include bytes that are ASCII control
characters, you just prevented *most* valid UTF-8 names.

On the other hand, it's a really nice summary of the issues and *does* have a
lot of good info - I hadn't seen that particular use of GLOBIGNORE, for
instance.

Bottom line - supporting filenames humans actually want to use (as opposed to a
fascist FAT 8+3 format) is *hard*. ;)

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