Subject: Re: [PATCH] FS: ext4: fix integer overflow in alloc_flex_gd()
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From: Xi Wang <xi.wang@gmail.com>
In-Reply-To: <4F42DBA0.4090502@redhat.com>
Date: Tue, 21 Feb 2012 08:55:57 -0500
Cc: Haogang Chen <haogangchen@gmail.com>, Theodore Tso <tytso@mit.edu>,
        Andreas Dilger <adilger.kernel@dilger.ca>, linux-ext4@vger.kernel.org,
        linux-kernel@vger.kernel.org, Yongqiang Yang <xiaoqiangnk@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>
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To: Eric Sandeen <sandeen@redhat.com>
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On Feb 20, 2012, at 6:47 PM, Eric Sandeen wrote:
> Hm this raises a few questions I think.
> 
> On the one hand, making sure the kmalloc arg doesn't overflow here is
> certainly a good thing and probably the right thing to do in the short term.
> 
> So I guess:
> 
> Reviewed-by: Eric Sandeen <sandeen@redhat.com>
> 
> for that, to close the hole.

Another possibility is to wait for knalloc/kmalloc_array in the -mm
tree, which is basically the non-zeroing version of kcalloc that
performs overflow checking.

> Doesn't this also mean that a valid s_log_groups_per_flex (i.e. 31)
> will fail in this resize code?  That would be an unexpected outcome.
> 2^31 groups per flex is a little crazy, but still technically valid
> according to the limits in the code.

Or we could limit s_log_groups_per_flex/groups_per_flex to a
reasonable upper bound in ext4_fill_flex_info(), right?

- xi

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