Re: [PATCH 08/26] xfs: hide metadata inodes from everyone because they are special

[Dave Chinner <david@fromorbit.com>]

On Thu, Aug 22, 2024 at 05:04:14PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> Metadata inodes are private files and therefore cannot be exposed to
> userspace.  This means no bulkstat, no open-by-handle, no linking them
> into the directory tree, and no feeding them to LSMs.  As such, we mark
> them S_PRIVATE, which stops all that.

Can you merge this back up into the initial iget support code?

> 
> While we're at it, put them in a separate lockdep class so that it won't
> get confused by "recursive" i_rwsem locking such as what happens when we
> write to a rt file and need to allocate from the rt bitmap file.  The
> static function that we use to do this will be exported in the rtgroups
> patchset.

Stale commit message? There's nothing of the sort in this patch....

> 
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
>  fs/xfs/scrub/tempfile.c |    8 ++++++++
>  fs/xfs/xfs_iops.c       |   15 ++++++++++++++-
>  2 files changed, 22 insertions(+), 1 deletion(-)
> 
> 
> diff --git a/fs/xfs/scrub/tempfile.c b/fs/xfs/scrub/tempfile.c
> index 177f922acfaf1..3c5a1d77fefae 100644
> --- a/fs/xfs/scrub/tempfile.c
> +++ b/fs/xfs/scrub/tempfile.c
> @@ -844,6 +844,14 @@ xrep_is_tempfile(
>  	const struct xfs_inode	*ip)
>  {
>  	const struct inode	*inode = &ip->i_vnode;
> +	struct xfs_mount	*mp = ip->i_mount;
> +
> +	/*
> +	 * Files in the metadata directory tree also have S_PRIVATE set and
> +	 * IOP_XATTR unset, so we must distinguish them separately.
> +	 */
> +	if (xfs_has_metadir(mp) && (ip->i_diflags2 & XFS_DIFLAG2_METADATA))
> +		return false;

Why do you need to check both xfs_has_metadir() and the inode flag
here? The latter should only be set if the former is set, yes?
If it's the other way around, then we have an on-disk corruption...

>  	if (IS_PRIVATE(inode) && !(inode->i_opflags & IOP_XATTR))
>  		return true;

> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 1cdc8034f54d9..c1686163299a0 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -42,7 +42,9 @@
>   * held. For regular files, the lock order is the other way around - the
>   * mmap_lock is taken during the page fault, and then we lock the ilock to do
>   * block mapping. Hence we need a different class for the directory ilock so
> - * that lockdep can tell them apart.
> + * that lockdep can tell them apart.  Directories in the metadata directory
> + * tree get a separate class so that lockdep reports will warn us if someone
> + * ever tries to lock regular directories after locking metadata directories.
>   */
>  static struct lock_class_key xfs_nondir_ilock_class;
>  static struct lock_class_key xfs_dir_ilock_class;
> @@ -1299,6 +1301,7 @@ xfs_setup_inode(
>  {
>  	struct inode		*inode = &ip->i_vnode;
>  	gfp_t			gfp_mask;
> +	bool			is_meta = xfs_is_metadata_inode(ip);
>  
>  	inode->i_ino = ip->i_ino;
>  	inode->i_state |= I_NEW;
> @@ -1310,6 +1313,16 @@ xfs_setup_inode(
>  	i_size_write(inode, ip->i_disk_size);
>  	xfs_diflags_to_iflags(ip, true);
>  
> +	/*
> +	 * Mark our metadata files as private so that LSMs and the ACL code
> +	 * don't try to add their own metadata or reason about these files,
> +	 * and users cannot ever obtain file handles to them.
> +	 */
> +	if (is_meta) {
> +		inode->i_flags |= S_PRIVATE;
> +		inode->i_opflags &= ~IOP_XATTR;
> +	}

No need for a temporary variable here.

-Dave.
-- 
Dave Chinner
david@fromorbit.com