linux-ext4 - Re: [PATCH] ext4: Fix data corruption for mmap writes

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Message-ID: <20170526230254.rcogrq2dolk7uqfk@thunk.org>
Date:   Fri, 26 May 2017 19:02:54 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org, Michael Zimmer <michael@...rm64.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] ext4: Fix data corruption for mmap writes

On Thu, May 25, 2017 at 01:46:22PM +0200, Jan Kara wrote:
> mpage_submit_page() can race with another process growing i_size and
> writing data via mmap to the written-back page. As mpage_submit_page()
> samples i_size too early, it may happen that ext4_bio_write_page()
> zeroes out too large tail of the page and thus corrupts user data.
> 
> Fix the problem by sampling i_size only after the page has been
> write-protected in page tables by clear_page_dirty_for_io() call.
> 
> Reported-by: Michael Zimmer <michael@...rm64.com>
> CC: stable@...r.kernel.org
> Fixes: cb20d5188366f04d96d2e07b1240cc92170ade40
> Signed-off-by: Jan Kara <jack@...e.cz>

Thanks, applied.

					- Ted