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

YueHaibing
2019-02-20T09:10:38Z

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@huawei.com>
>>> ---
>>> 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
>
>
> .
>