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

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Message-ID: <20250117180914.76c5fb05@kmaincent-XPS-13-7390>
Date: Fri, 17 Jan 2025 18:09:14 +0100
From: Kory Maincent <kory.maincent@...tlin.com>
To: "David S. Miller" <davem@...emloft.net>, Kory Maincent
 <kory.maincent@...tlin.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: 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>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
 <pabeni@...hat.com>
Subject: Re: [PATCH net-next] net: phy: Fix suspicious rcu_dereference usage

On Fri, 17 Jan 2025 15:14:45 +0100
Kory Maincent <kory.maincent@...tlin.com> wrote:

> The phy_detach function can be called with or without the rtnl lock held.
> When the rtnl lock is not held, using rtnl_dereference() triggers a
> warning due to the lack of lock context.
> 
> Add an rcu_read_lock() to ensure the lock is acquired and to maintain
> synchronization.

Sent the wrong patch which have a ; missing.

pw-bot: cr

> 
> Tested-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> Reported-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> Closes:
> https://lore.kernel.org/netdev/4c6419d8-c06b-495c-b987-d66c2e1ff848@tuxon.dev/
> Fixes: 35f7cad1743e ("net: Add the possibility to support a selected hwtstamp
> in netdevice") Signed-off-by: Kory Maincent <kory.maincent@...tlin.com> ---
>  drivers/net/phy/phy_device.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 5b34d39d1d52..b9b9aa16c10a 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -2001,12 +2001,14 @@ void phy_detach(struct phy_device *phydev)
>  	if (dev) {
>  		struct hwtstamp_provider *hwprov;
>  
> -		hwprov = rtnl_dereference(dev->hwprov);
> +		rcu_read_lock()
> +		hwprov = rcu_dereference(dev->hwprov);
>  		/* Disable timestamp if it is the one selected */
>  		if (hwprov && hwprov->phydev == phydev) {
>  			rcu_assign_pointer(dev->hwprov, NULL);
>  			kfree_rcu(hwprov, rcu_head);
>  		}
> +		rcu_read_unlock();
>  
>  		phydev->attached_dev->phydev = NULL;
>  		phydev->attached_dev = NULL;



-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com