linux-kernel - Re: A pass-through support for NFSv4 style ACL

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Date:   Wed, 17 May 2023 05:58:37 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Christian Brauner <brauner@...nel.org>
Cc:     Ondrej Valousek <ondrej.valousek.xm@...esas.com>,
        "trondmy@...merspace.com" <trondmy@...merspace.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andreas Gruenbacher <agruenba@...hat.com>
Subject: Re: A pass-through support for NFSv4 style ACL

On Wed, 2023-05-17 at 09:42 +0200, Christian Brauner wrote:
> On Tue, May 16, 2023 at 05:22:30PM -0400, Jeff Layton wrote:
> > On Tue, 2023-05-16 at 20:50 +0000, Ondrej Valousek wrote:
> > > 
> > > Hi Christian,
> > > 
> > > Would it be possible to patch kernel the way it accepts native (i.e no
> > > conversion to Posix ACL) NFSv4 style ACLs for filesystems that can
> > > support them?
> > > I.E. OpenZFS, NTFS, could be also interesting for Microsofts WSL2  or
> > > Samba right?
> > > 
> > > I mean, I am not trying to push richacl again knowing they have been
> > > rejected, but just NFS4 style Acls as they are so similar to Windows
> > > ACLs.
> > > 
> > 
> > Erm, except you kind of are if you want to do this. I don't see how this
> > idea works unless you resurrect RichACLs or something like them.
> 
> I have no idea about the original flame war that ended RichACLs in
> additition to having no clear clue what RichACLs are supposed to
> achieve. My current knowledge extends to "Christoph didn't like them".
> 
> > 
> > > The idea here would be that we could
> > > - mount NTFS/ZFS filesystem and inspect ACLs using existing tools
> > > (nfs4_getacl)
> > > - share with NFSv4 in a pass through mode
> > > - in Windows WSL2 we could inspect local filesystem ACLs using the
> > > same tools
> > > 
> > > Does it make any sense or it would require lot of changes to VFS
> > > subsystem or its a nonsense altogether?
> 
> Yes, very likely.
> 
> We'd either have to change the current inode operations for getting and
> setting acls to take a new struct acl that can contain either posix acls
> or rich acls or add new ones just for these new fangled ones.
> 
> Choosing the first - more sensible - of these two options will mean
> updating each filesystem's acl inode operations. Might turn out to not
> be invasive code as it might boil down to struct posix_acl *acl =
> acl->posix at the beginning of each method but still.
> 
> Then we'd probably also need to:
> 
> * handle permission checking (see Jeff's comment below)
> * change/update the ACL caching layer
> * if the past hast taught me anything then overlayfs would probably need
>   some additional logic as well
> 

Yeah, it's a significant project.

> > > 
> > 
> > Eventually you have to actually enforce the ACL. Do NTFS/ZFS already
> > have code to do this? If not then someone would need to write it.
> > 
> > Also windows and nfs acls do have some differences, so you'll need a
> > translation layer too.
> 
> Jeff, I know you have some knowledge in this area you probably are
> better equipped to judge the sanity and feasibility of this.

I know a bit, but Andreas (cc'ed) is the undisputed expert. If you're
looking to resurrect this effort, then you should definitely loop him
in.

-- 
Jeff Layton <jlayton@...nel.org>