Re: [patch] xfs: check for underflow in xfs_iformat_fork()

[Jeff Liu <jeff.liu@oracle.com>]

On 08/27/2013 12:12 AM, Ben Myers wrote:

> Hey Dan,
> 
> On Mon, Aug 26, 2013 at 05:37:15PM +0300, Dan Carpenter wrote:
>> On Fri, Aug 23, 2013 at 12:36:13PM -0500, Ben Myers wrote:
>>> Dan,
>>>
>>> On Fri, Aug 16, 2013 at 08:26:50AM +1000, Dave Chinner wrote:
>>>> On Thu, Aug 15, 2013 at 09:37:06AM -0500, Ben Myers wrote:
>>>>> Hey Dan & Jeff,
>>>>>
>>>>> On Thu, Aug 15, 2013 at 06:10:43PM +0800, Jeff Liu wrote:
>>>>>> On 08/15/2013 01:53 PM, Dan Carpenter wrote:
>>>>>>
>>>>>>> The "di_size" variable comes from the disk and it's a signed 64 bit.
>>>>>>> We check the upper limit but we should check for negative numbers as
>>>>>>> well.
>>>>>>>
>>>>>>> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
>>>>>>>
>>>>>>> diff --git a/fs/xfs/xfs_inode_fork.c b/fs/xfs/xfs_inode_fork.c
>>>>>>> index 123971b..849fc70 100644
>>>>>>> --- a/fs/xfs/xfs_inode_fork.c
>>>>>>> +++ b/fs/xfs/xfs_inode_fork.c
>>>>>>> @@ -167,7 +167,8 @@ xfs_iformat_fork(
>>>>>>>  			}
>>>>>>>  
>>>>>>>  			di_size = be64_to_cpu(dip->di_size);
>>>>>>> -			if (unlikely(di_size > XFS_DFORK_DSIZE(dip, ip->i_mount))) {
>>>>>>> +			if (unlikely(di_size < 0 ||
>>>>>>
>>>>>> But the di_size is initialized to ZERO while allocating a new inode on disk.
>>>>>> I wonder if that is better to ASSERT in this case because the current check
>>>>>> is used to make sure that the item is inlined, or we don't need it at all.
>>>>>
>>>>> Hmm.  Dan's additional check looks good to me.  In this case I'd say the forced
>>>>> shutdown is more appropriate than an assert, because here we're reading the
>>>>> inode from disk, as opposed to looking at a structure that is already incore
>>>>> which we think we've initialized.  We want to handle unexpected inputs from
>>>>> disk without crashing even if we are CONFIG_XFS_DEBUG.
>>>>
>>>> There are lots of places where we only check di_size to be greater
>>>> than some value, and don't check for it being less than zero. Hence
>>>> I think that a better solution might be to di_size unsigned as that
>>>> will catch "negative" sizes for all types of situations.
>>>
>>> What do you say to making di_size unsigned?  Any interest?
>>>
>>
>> I'm not the right person to change "lots of places".  Some of these
>> are probably subtle.  Just give me the reported-by and I'm happy.
> 
> I'll apply this for now, and we'll see if someone is interested enough to pick
> up the rest.

Hi Ben,

I just back from a longer vacation, will take care of the rest.

Thanks,
-Jeff

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