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Date: Fri, 6 Oct 2017 07:57:01 -0700
From: Matthew Wilcox <willy@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: "J. Bruce Fields" <bfields@fieldses.org>,
        "Theodore Ts'o" <tytso@mit.edu>, Adam Borowski <kilobyte@angband.pl>,
        Al Viro <viro@ZenIV.linux.org.uk>, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] vfs: hard-ban creating files with control characters in
 the name
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On Fri, Oct 06, 2017 at 01:09:42PM +1100, Dave Chinner wrote:
> On Thu, Oct 05, 2017 at 12:16:19PM -0400, J. Bruce Fields wrote:
> > This kind of restriction sounds more like a permanent feature of the
> > filesystem--something you'd set at mkfs time.
> > 
> > We already have filesystems with these kinds of restrictions, don't we?
> 
> In general, no. Filename storage typically defined  in the
> filesystem on-disk formats as an opaque string of bytes - the
> filesystem has no business parsing them to determine validity of the
> bytes. Think encrypted filenames and the like - control characters
> in the on-disk format are most definitely necessary and therefore
> must be legal.

Umm.  But filenames still can't have / or \0 in them, so your encryption
already has to avoid at least two special characters.

I agree with your main point though; there is no advantage to doing this
in each individual filesystem.