linux-kernel - Re: [patch 1/9] fs: libfs buffered write leak fix

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Date:	Sun, 4 Feb 2007 04:55:49 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Jörn Engel <joern@...ybastard.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Filesystems <linux-fsdevel@...r.kernel.org>,
	Linux Memory Management <linux-mm@...ck.org>
Subject: Re: [patch 1/9] fs: libfs buffered write leak fix

On Sat, Feb 03, 2007 at 05:49:47PM +0000, Jörn Engel wrote:
> On Sat, 3 February 2007 02:33:16 +0100, Nick Piggin wrote:
> > 
> > If doing a partial-write, simply clear the whole page and set it uptodate
> > (don't need to get too tricky).
> 
> That sounds just like a bug I recently fixed in logfs.  prepare_write()
> would clear the page, commit_write() would write the whole page.  Bug
> can be reproduced with a simple testcate:
> 
> echo -n foo > foo
> echo -n bar >> foo
> cat foo
> 
> With the bug, the second write will replace "foo" with "\0\0\0" and
> cat will return "bar".  Doing a read instead of clearing the page will
> return "foobar", as would be expected.
> 
> Can you hit the same bug with your patch or did I miss something?

Yes, the page is only cleared if it is not uptodate. This is fine
for the simple filesystems.
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