netdev - Re: [PATCH net-next] net: phylink: fix NULL pl->pcs dereference during phylink_pcs_poll

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Message-ID: <Yr24QzzcS1dMVtl0@shell.armlinux.org.uk>
Date:   Thu, 30 Jun 2022 15:50:43 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Nicolas Ferre <nicolas.ferre@...rochip.com>
Cc:     Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Claudiu Beznea <Claudiu.Beznea@...rochip.com>,
        Santiago Esteban <Santiago.Esteban@...rochip.com>
Subject: Re: [PATCH net-next] net: phylink: fix NULL pl->pcs dereference
 during phylink_pcs_poll_start

On Thu, Jun 30, 2022 at 03:46:54PM +0200, Nicolas Ferre wrote:
> Vladimir, Russell,
> 
> On 29/06/2022 at 21:33, Vladimir Oltean wrote:
> > The current link mode of the phylink instance may not require an
> > attached PCS. However, phylink_major_config() unconditionally
> > dereferences this potentially NULL pointer when restarting the link poll
> > timer, which will panic the kernel.
> > 
> > Fix the problem by checking whether a PCS exists in phylink_pcs_poll_start(),
> > otherwise do nothing. The code prior to the blamed patch also only
> > looked at pcs->poll within an "if (pcs)" block.
> > 
> > Fixes: bfac8c490d60 ("net: phylink: disable PCS polling over major configuration")
> > Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> > ---
> >   drivers/net/phy/phylink.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
> > index 1a7550f5fdf5..48f0b9b39491 100644
> > --- a/drivers/net/phy/phylink.c
> > +++ b/drivers/net/phy/phylink.c
> > @@ -766,7 +766,7 @@ static void phylink_pcs_poll_stop(struct phylink *pl)
> >   static void phylink_pcs_poll_start(struct phylink *pl)
> >   {
> > -	if (pl->pcs->poll && pl->cfg_link_an_mode == MLO_AN_INBAND)
> > +	if (pl->pcs && pl->pcs->poll && pl->cfg_link_an_mode == MLO_AN_INBAND)
> >   		mod_timer(&pl->link_poll, jiffies + HZ);
> >   }
> 
> Fixes the NULL pointer on my boards:
> Tested-by: Nicolas Ferre <nicolas.ferre@...rochip.com> # on sam9x60ek

Thanks all, hopefully it'll get applied to net-next soon.

Sadly, this slipped through my testing, as the only platform I have
access to at the moment always supplies a PCS (mvneta based) so there's
no way my testing would ever have caught this. Sorry for the problems.

-- 
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