linux-ext4 - Re: [PATCH] mm: add missing mutex lock arround notify

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Message-ID: <20111220224558.GA27615@thunk.org>
Date:	Tue, 20 Dec 2011 17:45:58 -0500
From:	Ted Ts'o <tytso@....edu>
To:	Al Viro <viro@...IV.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Djalal Harouni <tixxdz@...ndz.org>,
	Hugh Dickins <hughd@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Wu Fengguang <fengguang.wu@...el.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Neil Brown <neilb@...e.de>,
	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>,
	Christoph Hellwig <hch@...radead.org>,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] mm: add missing mutex lock arround notify_change

I just took a closer look, and we don't need to take immediate action;
there is no security issue here were someone could modify a writable
suid file as I had originally feared.  It's not as obvious as it could
be because of how the code is broken up, but in mext_check_arguments()
in fs/ext4/move_extent.c, we return with an error if the donor file
has the SUID or SGID bit set, so we'll never actually end up calling
file_remove_suid().  So in fact the right patch is just to remove the
call to file_remove_suid() altogether.

						- Ted
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