Re: [PATCH] staging: erofs: harden inode lookup for 32-bit platforms

[Gao Xiang]

Hi Dan,

On 2018/10/11 19:12, Dan Carpenter wrote:
> On Thu, Oct 11, 2018 at 06:49:57PM +0800, Gao Xiang wrote:
>> Hi Dan,
>>
>> On 2018/10/11 18:18, Dan Carpenter wrote:
>>> On Thu, Oct 11, 2018 at 05:46:26PM +0800, Gao Xiang wrote:
>>>>
>>>>
>>>> On 2018/10/11 16:44, Dan Carpenter wrote:
>>>>> On Tue, Oct 09, 2018 at 10:07:13PM +0800, Gao Xiang wrote:
>>>>>> This patch introduces inode hash function, test and set callbacks,
>>>>>> and iget5_locked to find the right inode for 32-bit platforms.
>>>>>>
>>>>>
>>>>> The way I read this changelog, we're trying to deal with corrupt file
>>>>> systems?  Is that correct?  Presumably in the current code it could lead
>>>>> to a Oops or something?
>>>>
>>>> No, this commit isn't trying to deal with corrupt file systems.
>>>> In EROFS, the nid is not continuous and it represents the inode offset
>>>> inode offset = nid * 32.
>>>> Therefore the nid is 64-bit both for 32-bit and 64-bit platforms. However,
>>>> i_ino is 'unsigned long', which means for 32-bit platforms, i_ino is not enough
>>>> to contain the nid.
>>>>
>>>> Therefore, we should use iget5_locked for this case.
>>>
>>> I guess what I'm saying is, what are the user visible effects of this
>>> patch?  It's hard for me to tell from the patch description.  Could you
>>> please re-write the description and send a v2?
>>
>> Sorry for my just hurry reply. It seems I really misunderstood your point :-(
>>
>> If all nids are less than 32-bit, the user will see the correct inode/nid number
>> for all 32-bit platforms, but if some nids are greater than 32-bit, it could be
>> collisions without this patch for 32-bit platforms.
>>
>> This patch switch the inode number by XOR the high 32-bit and the low 32-bit,
>> use customized tester to avoid collisions for 32-bit platforms.
>>
>> I will send v2 to fix the commit message...but it seems Greg is already merged in
>> https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git/commit/?h=staging-testing&id=2abd7814138774eb56319e9dcc0abd08ece45424
>>
> 
> Oh.  Then that's fine then.  If Greg already merged it, then it's too
> late to change.  Thanks for the explanation, though.

I appended the v2 patch in the end of this reply for reference...

Thanks,
Gao Xiang

> 
> regards,
> dan carpenter
>