Re: [PATCH] xfs: correct statx's result_mask value

["Darrick J. Wong" <darrick.wong@oracle.com>]

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...

...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?

--D

>  
>  	if (ip->i_d.di_flags & XFS_DIFLAG_IMMUTABLE)
>  		stat->attributes |= STATX_ATTR_IMMUTABLE;
> -- 
> 2.7.4
> 
> 
>