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

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

[Kory Maincent]

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.

Tested-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reported-by: Claudiu Beznea <claudiu.beznea.uj@bp.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@bootlin.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;
-- 
2.34.1

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

[Kory Maincent]

On Fri, 17 Jan 2025 15:14:45 +0100
Kory Maincent <kory.maincent@bootlin.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@bp.renesas.com>
> Reported-by: Claudiu Beznea <claudiu.beznea.uj@bp.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@bootlin.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