Re: [PATCH 1/2] xfs: use setattr_copy to set vfs inode attributes

[Dave Chinner <david@fromorbit.com>]

On Wed, Mar 09, 2022 at 11:22:11AM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> Filipe Manana pointed out that XFS' behavior w.r.t. setuid/setgid
> revocation isn't consistent with btrfs[1] or ext4.  Those two
> filesystems use the VFS function setattr_copy to convey certain
> attributes from struct iattr into the VFS inode structure.
> 
> Andrey Zhadchenko reported[2] that XFS uses the wrong user namespace to
> decide if it should clear setgid and setuid on a file attribute update.
> This is a second symptom of the problem that Filipe noticed.
> 
> XFS, on the other hand, open-codes setattr_copy in xfs_setattr_mode,
> xfs_setattr_nonsize, and xfs_setattr_time.  Regrettably, setattr_copy is
> /not/ a simple copy function; it contains additional logic to clear the
> setgid bit when setting the mode, and XFS' version no longer matches.
> 
> The VFS implements its own setuid/setgid stripping logic, which
> establishes consistent behavior.  It's a tad unfortunate that it's
> scattered across notify_change, should_remove_suid, and setattr_copy but
> XFS should really follow the Linux VFS.  Adapt XFS to use the VFS
> functions and get rid of the old functions.
> 
> [1] https://lore.kernel.org/fstests/CAL3q7H47iNQ=Wmk83WcGB-KBJVOEtR9+qGczzCeXJ9Y2KCV25Q@mail.gmail.com/
> [2] https://lore.kernel.org/linux-xfs/20220221182218.748084-1-andrey.zhadchenko@virtuozzo.com/
> 
> Fixes: f736d93d76d3 ("xfs: support idmapped mounts")
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
>  fs/xfs/xfs_iops.c |   56 +++--------------------------------------------------
>  fs/xfs/xfs_pnfs.c |    3 ++-
>  2 files changed, 5 insertions(+), 54 deletions(-)

Looks good, nice cleanup as well as being more correct.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
-- 
Dave Chinner
david@fromorbit.com