linux-kernel - [PATCH net-next v2] net: phy: Fix suspicious rcu

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Message-Id: <20250117173645.1107460-1-kory.maincent@bootlin.com>
Date: Fri, 17 Jan 2025 18:36:44 +0100
From: Kory Maincent <kory.maincent@...tlin.com>
To: Kory Maincent <kory.maincent@...tlin.com>,
	"David S. Miller" <davem@...emloft.net>,
	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: [PATCH net-next v2] net: phy: Fix suspicious rcu_dereference usage

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@...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>
---

Changes in v2:
- Add a missing ;
---
 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..3eeee7cba923 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