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

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Message-ID: <bfe3b0a0-5f42-6c32-6de7-4d989544e488@microchip.com>
Date:   Thu, 30 Jun 2022 15:46:54 +0200
From:   Nicolas Ferre <nicolas.ferre@...rochip.com>
To:     Vladimir Oltean <vladimir.oltean@....com>, <netdev@...r.kernel.org>
CC:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Russell King <linux@...linux.org.uk>,
        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

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

Best regards,
   Nicolas


-- 
Nicolas Ferre