netdev - Re: [PATCH net-next v3] net: phy: Fix suspicious rcu

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Message-ID: <20250122171229.3e0b2111@kmaincent-XPS-13-7390>
Date: Wed, 22 Jan 2025 17:12:29 +0100
From: Kory Maincent <kory.maincent@...tlin.com>
To: Paul Barker <paul.barker.ct@...renesas.com>
Cc: Jakub Kicinski <kuba@...nel.org>, "David S. Miller"
 <davem@...emloft.net>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, Claudiu Beznea
 <claudiu.beznea.uj@...renesas.com>, thomas.petazzoni@...tlin.com, Andrew
 Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>, Russell King
 <linux@...linux.org.uk>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>, Niklas Söderlund
 <niklas.soderlund@...natech.se>, Sergey Shtylyov <s.shtylyov@....ru>
Subject: Re: [PATCH net-next v3] net: phy: Fix suspicious rcu_dereference
 usage

On Wed, 22 Jan 2025 14:03:37 +0000
Paul Barker <paul.barker.ct@...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@...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
https://bootlin.com