Re: [PATCH] fat: Support fallocate on fat.

[OGAWA Hirofumi]

Namjae Jeon <linkinjeon@xxxxxxxxx> 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.

> 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.

Thanks.
-- 
OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
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