linux-kernel - Re: [PATCH] fat: Support fallocate on fat.

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Message-ID: <CAKYAXd-OD_3Z8=6mBQMvBApje9sN0EiPX8drMXc6pSeMgG8Nnw@mail.gmail.com>
Date:	Mon, 9 Jul 2012 20:14:50 +0900
From:	Namjae Jeon <linkinjeon@...il.com>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Ravishankar N <cyberax82@...il.com>,
	Amit Sahrawat <amit.sahrawat83@...il.com>
Subject: Re: [PATCH] fat: Support fallocate on fat.

2012/7/9, OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>:
> Namjae Jeon <linkinjeon@...il.com> writes:
>
>>>> +	/*
>>>> +	 * calculate i_blocks and mmu_private from the actual number of
>>>> +	 * allocated clusters instead of doing it from file size.This ensures
>>>> +	 * that the preallocated disk space using FALLOC_FL_KEEP_SIZE is
>>>> +	 * persistent across remounts and writes go into the allocated
>>>> clusters.
>>>> +	 */
>>>> +	fat_calc_dir_size(inode);
>>>
>>> Looks like the wrong. If you didn't initialize preallocated space, the
>>> data never be exposed to userland. It is security bug.
>> As explained above, if we do append write instead of seeking into a
>> random offset, there is no security risk.
>
> So it means? - if we didn't, there is.
Yes, right.
>
>> The main disadvantage with initializing the preallocated space (as is
>> done in case of without FALLOC_FL_KEEP_SIZE ) is it takes long time
>> for bigger allocation sizes. It took ~70 seconds to preallocate 2GB on
>> our target if FALLOC_FL_KEEP_SIZE is not set.
>
> It doesn't become the reason to expose uninitialized data.
I agree.. If I try to change code for initializing the preallocated
space, Is this patch acceptable ?

Thanks Ogawa.
>
> Thanks.
> --
> OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
>
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