linux-ext4 - Re: [PATCH 00/12] acl: remove remaining posix acl handlers

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Date:   Mon, 30 Jan 2023 10:16:15 +0100
From:   Christoph Hellwig <hch@....de>
To:     Christian Brauner <brauner@...nel.org>
Cc:     linux-fsdevel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        Al Viro <viro@...iv.linux.org.uk>,
        Seth Forshee <sforshee@...nel.org>,
        linux-erofs@...ts.ozlabs.org, Jan Kara <jack@...e.com>,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-mtd@...ts.infradead.org, ocfs2-devel@....oracle.com,
        reiserfs-devel@...r.kernel.org
Subject: Re: [PATCH 00/12] acl: remove remaining posix acl handlers

On Mon, Jan 30, 2023 at 10:10:52AM +0100, Christian Brauner wrote:
> However, a few filesystems still rely on the ->list() method of the
> generix POSIX ACL xattr handlers in their ->listxattr() inode operation.
> This is a very limited set of filesystems. For most of them there is no
> dependence on the generic POSIX ACL xattr handler in any way.
> 
> In addition, during inode initalization in inode_init_always() the
> registered xattr handlers in sb->s_xattr are used to raise IOP_XATTR in
> inode->i_opflags.
> 
> With the incoming removal of the legacy POSIX ACL handlers it is at
> least possible for a filesystem to only implement POSIX ACLs but no
> other xattrs. If that were to happen we would miss to raise IOP_XATTR
> because sb->s_xattr would be NULL. While there currently is no such
> filesystem we should still make sure that this just works should it ever
> happen in the future.

Now the real questions is: do we care?  Once Posix ACLs use an
entirely separate path, nothing should rely on IOP_XATTR for them.
So instead I think we're better off auditing all users of IOP_XATTR
and making sure that nothing relies on them for ACLs, as we've very
much split the VFS concept of ACLs from that from xattrs otherwise.