linux-kernel - Re: [PATCH] ext4: avoid exposure of stale data in ext4_punch

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Message-ID: <20140221094550.GD12506@quack.suse.cz>
Date:	Fri, 21 Feb 2014 10:45:50 +0100
From:	Jan Kara <jack@...e.cz>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Jan Kara <jack@...e.cz>, Maxim Patlasov <MPatlasov@...allels.com>,
	adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ext4: avoid exposure of stale data in ext4_punch_hole()
 -v2

On Thu 20-02-14 19:21:07, Ted Tso wrote:
> On Fri, Sep 27, 2013 at 06:05:17PM +0200, Jan Kara wrote:
> > On Fri 27-09-13 19:54:03, Maxim Patlasov wrote:
> > > While handling punch-hole fallocate, it's useless to truncate page cache
> > > before removing the range from extent tree (or block map in indirect case)
> > > because page cache can be re-populated (by read-ahead or read(2) or mmap-ed
> > > read) immediately after truncating page cache, but before updating extent
> > > tree (or block map). In that case the user will see stale data even after
> > > fallocate is completed.
> > > 
> > > Changed in v2 (Thanks to Jan Kara):
> > >  - Until the problem of data corruption resulting from pages backed by
> > >    already freed blocks is fully resolved, the simple thing we can do now
> > >    is to add another truncation of pagecache after punch hole is done.
> >   The patch looks good. You can add:
> > Reviewed-by: Jan Kara <jack@...e.cz>
> 
> I was going through old patches, and it looks like this one got
> dropped.  My apologies.
> 
> As far as I can tell, the underlying problem in the VFS/MM layer
> hasn't been solved yet (Jan, can you confirm?), so I've queued this
> patch for the next merge window.
  Yes, we didn't solve it yet. Thanks for queueing the patch!

								Honza

-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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