Re: [PATCH -next] btrfs: Fix type conversion in btrfs_read_root_item

[YueHaibing]

On 2019/2/20 14:10, Dan Carpenter wrote:
> On Wed, Feb 20, 2019 at 08:58:43AM +0300, Dan Carpenter wrote:
>> On Wed, Feb 20, 2019 at 03:08:40AM +0000, YueHaibing wrote:
>>> btrfs_item_size_nr return value is u32, convert it to int may result
>>> in truncation.Also read_extent_buffer expect a unsigned param, so
>>> min_t should use type u32 to compare.
>>>
>>> Fixes: 8ea05e3a4262 ("Btrfs: introduce subvol uuids and times")
>>> Signed-off-by: YueHaibing <yuehaibing@xxxxxxxxxx>
>>> ---
>>>  fs/btrfs/root-tree.c | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/btrfs/root-tree.c b/fs/btrfs/root-tree.c
>>> index 02d1a57af78b..893d12fbfda0 100644
>>> --- a/fs/btrfs/root-tree.c
>>> +++ b/fs/btrfs/root-tree.c
>>> @@ -21,12 +21,12 @@ static void btrfs_read_root_item(struct extent_buffer *eb, int slot,
>>>  				struct btrfs_root_item *item)
>>>  {
>>>  	uuid_le uuid;
>>> -	int len;
>>> +	u32 len;
>>>  	int need_reset = 0;
>>>  
>>>  	len = btrfs_item_size_nr(eb, slot);
>>>  	read_extent_buffer(eb, item, btrfs_item_ptr_offset(eb, slot),
>>> -			min_t(int, len, (int)sizeof(*item)));
>>                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>> Yeah, min_t() should normally cast to unsigned and the extra cast is
>> silly.
>>
> 
> Btw, I shouldn't have had to dig through the patch to find the *real*
> reason you wrote it.  A better description would have said:
> 
>     There is a messy cast here:
> 
> 	min_t(int, len, (int)sizeof(*item)));
> 
>     min_t() should normally cast to unsigned.  It's not possible for
>     "len" to be negative, but if it were then then we definitely
>     wouldn't want to pass negatives to read_extent_buffer().  Also there
>     is an extra cast.
> 
>     This patch shouldn't affect runtime, it's just a clean up.

Yes, This just a cleanup, Thanks!

> 
> regards,
> dan carpenter
> 
> 
> .
>