Re: [PATCH net-next v3] net: phy: Fix suspicious rcu_dereference usage

Kory Maincent
2025-01-22T16:12:34Z

On Wed, 22 Jan 2025 14:03:37 +0000
Paul Barker <paul.barker.ct@bp.renesas.com> wrote:

> On 21/01/2025 16:11, Kory Maincent wrote:
> > On Tue, 21 Jan 2025 15:44:34 +0000
> > Paul Barker <paul.barker.ct@bp.renesas.com> wrote:
> >
> >> On 21/01/2025 13:01, Kory Maincent wrote:
> >>
> [...]
> [...]
> [...]
> >>
> >> ravb_ptp_stop() modifies a couple of device registers and calls
> >> ptp_clock_unregister(). I don't see anything to suggest that this
> >> requires the rtnl lock to be held, unless I am missing something.
> >
> > What happens if two ptp_clock_unregister() with the same ptp_clock pointer
> > are called simultaneously? From ravb_suspend and ravb_set_ringparam for
> > example. It may cause some errors.
> > For example the ptp->kworker pointer could be used after a kfree.
> > https://elixir.bootlin.com/linux/v6.12.6/source/drivers/ptp/ptp_clock.c#L416
> >
>
> I've dug into this some more today and looked at the suspend/resume
> paths of other Ethernet drivers for comparison.
>
> netif_device_detach() and netif_device_attach() seem to be safe to call
> without holding the rtnl lock, e.g. the stmmac driver does this.
>
> In the suspend path, we should hold the rtnl lock across the calls to
> ravb_wol_setup() and ravb_close().
>
> In the resume path, we should hold the rtnl lock across the calls to
> ravb_wol_restore() and ravb_open(). I don't think there is any harm in
> holding the rtnl lock while we call pm_runtime_force_resume(), so we can
> take the lock before checking priv->wol_enabled and release after
> calling ravb_open().
>
> How does that sound?

Yes that sound nice, and similar to what I thought.
I will send a patch, I also found the same issue on sh_eth driver.

Regards
--
Köry Maincent, Bootlin
Embedded Linux and kernel engineering