linux-kernel - Re: [PATCH v3 09/18] nvmet-fcloop: prevent double port deletion

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Message-ID: <dbef52cf-a112-4fbd-b1ad-c9eebc1f4787@flourine.local>
Date: Tue, 18 Mar 2025 14:55:44 +0100
From: Daniel Wagner <dwagner@...e.de>
To: Hannes Reinecke <hare@...e.de>
Cc: Daniel Wagner <wagi@...nel.org>, 
	James Smart <james.smart@...adcom.com>, Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>, 
	Chaitanya Kulkarni <kch@...dia.com>, Keith Busch <kbusch@...nel.org>, linux-nvme@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 09/18] nvmet-fcloop: prevent double port deletion

On Tue, Mar 18, 2025 at 12:15:04PM +0100, Hannes Reinecke wrote:
> >   fcloop_remoteport_delete(struct nvme_fc_remote_port *remoteport)
> >   {
> >   	struct fcloop_rport *rport = remoteport->private;
> > +	bool delete_port = true;
> >   	unsigned long flags;
> >   	flush_work(&rport->ls_work);
> >   	spin_lock_irqsave(&fcloop_lock, flags);
> > +	if (test_and_set_bit(PORT_DELETE, &rport->flags))
> > +		delete_port = false;
> >   	rport->nport->rport = NULL;
> >   	spin_unlock_irqrestore(&fcloop_lock, flags);
> Can't you just check for a NULL rport->nport->rport pointer
> and do away with the PORT_DELETE flag?

Unfortunately, nport->rport is also set to NULL in __unlink_remote_port
and __unlink_target_port. If we would just update the pointer here, it
would be possible.

I played a bit around when to clear the nport->rport pointer but it
didn't work. There were always some UAFs or NULL pointer accesses. With
the flags I was able to get it fixed. I am not insisting on this
solution, just trying to explain why I choosed it.