Re: [PATCH v2 1/2] btrfs: Fix superblock csum type check.

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

-------- Original Message  --------
Subject: Re: [PATCH v2 1/2] btrfs: Fix superblock csum type check.
From: David Sterba <dsterba@suse.cz>
To: Qu Wenruo <quwenruo@cn.fujitsu.com>
Date: 2015年04月27日 18:59

> On Mon, Apr 27, 2015 at 08:25:58AM +0800, Qu Wenruo wrote:
>>
>>
>> -------- Original Message  --------
>> Subject: Re: [PATCH v2 1/2] btrfs: Fix superblock csum type check.
>> From: David Sterba <dsterba@suse.cz>
>> To: Qu Wenruo <quwenruo@cn.fujitsu.com>
>> Date: 2015年04月24日 23:05
>>
>>> On Fri, Apr 24, 2015 at 09:12:40AM +0800, Qu Wenruo wrote:
>>>> --- a/fs/btrfs/ctree.h
>>>> +++ b/fs/btrfs/ctree.h
>>>> @@ -173,6 +173,7 @@ struct btrfs_ordered_sum;
>>>>
>>>>    /* csum types */
>>>>    #define BTRFS_CSUM_TYPE_CRC32	0
>>>> +#define BTRFS_CSUM_LAST_TYPE	0
>>>>
>>>>    static int btrfs_csum_sizes[] = { 4, 0 };
>>>
>>> I'd prefer to fix it by removing the 0 from btrfs_csum_sizes instead of
>>> introducing a define.
>>>
>>
>> Removing the zero seems not help for this case, as some one can still
>> craft a strange csum_type to access outside the array.
>
> The ARRAY_SIZE will be 1, so if a crafted csum will be anything than 0,
> then the check will catch it, no?
Oh, I forgot there is ARRAY_SIZE check.
Now deleting the 0 in array is definitely the cleanest fix.

Thanks,
Qu
>
>> So I introduce the new macro and use the new macro to compare with
>> csum_type without acess the array.
>
> The macro serves the same purpose as the ARRAY_SIZE macro and is always
> in sync with the btrfs_csum_size.
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