linux-kernel - Re: [PATCH] FS: ext4: fix integer overflow in alloc_flex

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Message-ID: <4F43C825.1040501@redhat.com>
Date:	Tue, 21 Feb 2012 10:36:53 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Xi Wang <xi.wang@...il.com>
CC:	Haogang Chen <haogangchen@...il.com>, Theodore Tso <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
	Yongqiang Yang <xiaoqiangnk@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] FS: ext4: fix integer overflow in alloc_flex_gd()

On 02/21/2012 07:55 AM, Xi Wang wrote:
> 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@...hat.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?

Depends on the "flex_bg" design intent, I guess.

I don't know if the 2^31 was an intended design limit, or just a
mathematical limit that based on container sizes etc...

I'd have to look at the resize code more carefully but I can't imagine
that it's imperative to allocate this stuff all at once.

-Eric

> - xi
> 

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