linux-kernel - Racy NLS behaviour in FAT (and possible other fs)

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Date:	Mon, 19 Feb 2007 16:53:46 +0100
From:	Pierre Ossman <drzeus-list@...eus.cx>
To:	hirofumi@...l.parknet.co.jp, LKML <linux-kernel@...r.kernel.org>
Subject: Racy NLS behaviour in FAT (and possible other fs)

Hi,

I'm experiencing a rather odd behaviour with the character set conversion. If I
mount a vfat fs with utf8 and then create a file with invalid utf-8 sequences,
the file will briefly exist with these invalid sequences, then quickly convert
to a stripped version.

I haven't found an easy way to catch the race, but if I have nautilus open it
tends to catch it now and then (I get a file name with "<?>" replacing each bad
byte).

The race also seems to corrupt the in-memory state of the fs now and then. I
managed to create a file where "ls" shows "?" for most fields. Data seemed to
have made it to disk ok though (fsck didn't complain and a remount showed
everything as it should be).

Third, there seems to be a problem with not all syscalls being subjected to the
NLS transformation. Example:

$ echo foo > baråäö.txt
$ ls
foo.txt
$ echo foo > baråäö.txt
bash: baråäö.txt: File exists

Rgds
-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  PulseAudio, core developer          http://pulseaudio.org
  rdesktop, core developer          http://www.rdesktop.org
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