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From:   "Su Yanjun <suyj.fnst@cn.fujitsu.com>" <suyj.fnst@cn.fujitsu.com>
Subject: Re: [PATCH] xfs: correct statx's result_mask value
To:     Eric Sandeen <sandeen@sandeen.net>,
        "Darrick J. Wong" <darrick.wong@oracle.com>
CC:     <linux-xfs@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <suyanjun218@gmail.com>
References: <1546854790-5233-1-git-send-email-suyj.fnst@cn.fujitsu.com>
 <20190107175229.GJ12689@magnolia>
 <2b27e2ec-368b-d24c-8443-e265f87e417c@sandeen.net>
Message-ID: <67e03af1-6e11-4236-76e6-6127b6cfb9b9@cn.fujitsu.com>
Date:   Tue, 8 Jan 2019 12:58:43 +0800
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On 1/8/2019 2:04 AM, Eric Sandeen wrote:
> On 1/7/19 11:52 AM, Darrick J. Wong wrote:
>> On Mon, Jan 07, 2019 at 04:53:10AM -0500, Su Yanjun wrote:
>>> For statx syscall, xfs return the wrong result_mask.
>>>
>>> Signed-off-by: Su Yanjun<suyj.fnst@cn.fujitsu.com>
>>> ---
>>>   fs/xfs/xfs_iops.c | 3 +++
>>>   1 file changed, 3 insertions(+)
>>>
>>> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
>>> index f48ffd7..3811457 100644
>>> --- a/fs/xfs/xfs_iops.c
>>> +++ b/fs/xfs/xfs_iops.c
>>> @@ -521,6 +521,9 @@ xfs_vn_getattr(
>>>   			stat->btime.tv_nsec = ip->i_d.di_crtime.t_nsec;
>>>   		}
>>>   	}
>>> +	
>>> +	/* Only return mask that we care */
>>> +	stat->result_mask &= request_mask;
>> Why not just:
>>
>> 	stat->result_mask = STATX_BASIC_STATS;
>>
>> at the top of the function?
>>
>> I don't see the need to mask off result_mask at all, since we could some
>> day elect to return more than what's in request_mask...
When we run xfstests with nfs, the generic/423 case runs failed. So i 
review the nfs'
nfs_getattr code it does validate the request_mask.

Then i review the xfs' getattr code, it has no such check. Whatever 
request_mask
  is set, the stat's result_mask always the 0x7ff.

Maybe it has Unclear semantics about statx's result_mask.
>> ...waitaminute, are you seeing garbage in the result_mask that's
>> returned to userspace?  I also noticed the vfs stat functions declare
>> "struct kstat stat;" without explicitly zeroing the structure fields,
>> which means (I think) that we can leak stack information if the kernel
>> isn't built with the stackleak plugin?
No such problem.
> A clear problem statement and reproducer steps would be hugely useful
> here.
>
> -Eric
Thanks,
Su