On 1/8/2019 2:04 AM, Eric Sandeen wrote:

On 1/7/19 11:52 AM, Darrick J. Wong wrote:

quoted

On Mon, Jan 07, 2019 at 04:53:10AM -0500, Su Yanjun wrote:

quoted

For statx syscall, xfs return the wrong result_mask.

Signed-off-by: Su Yanjun<redacted>
---
  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.

quoted

...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