linux-kernel - Re: [PATCH 1/2] vfs: Allow filesystems with foreign owner IDs to override UID checks

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Message-ID: <20251029-brust-reden-b61f1a55dc3b@brauner>
Date: Wed, 29 Oct 2025 13:39:45 +0100
From: Christian Brauner <brauner@...nel.org>
To: David Howells <dhowells@...hat.com>
Cc: Al Viro <viro@...iv.linux.org.uk>, 
	Christian Brauner <christian@...uner.io>, Marc Dionne <marc.dionne@...istor.com>, 
	Jeffrey Altman <jaltman@...istor.com>, Steve French <sfrench@...ba.org>, linux-afs@...ts.infradead.org, 
	openafs-devel@...nafs.org, linux-cifs@...r.kernel.org, linux-nfs@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Etienne Champetier <champetier.etienne@...il.com>, Chet Ramey <chet.ramey@...e.edu>, 
	Cheyenne Wills <cwills@...enomine.net>, Mimi Zohar <zohar@...ux.ibm.com>, 
	linux-integrity@...r.kernel.org
Subject: Re: [PATCH 1/2] vfs: Allow filesystems with foreign owner IDs to
 override UID checks

On Tue, Oct 21, 2025 at 02:20:21PM +0100, David Howells wrote:
> Christian Brauner <brauner@...nel.org> wrote:
> 
> > > +	if (unlikely(inode->i_op->have_same_owner)) {
> > 
> > Same, as above: similar to IOP_FASTPERM this should use a flag to avoid pointer derefs.
> 
> Can we do these IOP_* flags better?  Surely we can determine at the point the
> inode has its ->i_op assigned that these things are provided?  This optimises
> the case where they don't exist at the expense of the case where they do (we
> still have to check the pointer every time).
> 
> > > +	if (unlikely(inode->i_op->have_same_owner)) {

I think I mentioned this off-list. It looks like we can but I don't know
if there was any history behind not doing it that way. But please try.