linux-ext4 - Re: [PATCH] ext4: use atomic64_t for the per-flexbg free

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Message-ID: <20130312134519.GK18595@thunk.org>
Date:	Tue, 12 Mar 2013 09:45:19 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: use atomic64_t for the per-flexbg free_clusters
 count

On Mon, Mar 11, 2013 at 11:44:44PM -0400, Theodore Ts'o wrote:
> A user who was using a 8TB+ file system and with a very large flexbg
> size (> 65536) could cause the atomic_t used in the struct flex_groups
> to overflow.  This was detected by PaX security patchset:
> 
> http://forums.grsecurity.net/viewtopic.php?f=3&t=3289&p=12551#p12551
> 
> Fix this by using an atomic64_t for struct orlav_stats's
> free_clusters.
> 
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>

I should note that this bug was apparently introduced by commit
9f24e4208f7e, so it's been around for a while (since 2.6.30).
Fortunately it's a pretty rare corner case...

						- Ted
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