linux-kernel - [PATCH 1/2] net: phy: Check phydev->drv before dereferencing it

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Message-Id: <20231126141046.3505343-2-claudiu.beznea@tuxon.dev>
Date:   Sun, 26 Nov 2023 16:10:45 +0200
From:   Claudiu Beznea <claudiu.beznea@...on.dev>
To:     nicolas.ferre@...rochip.com, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        andrew@...n.ch, hkallweit1@...il.com, linux@...linux.org.uk,
        jgarzik@...ox.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Claudiu Beznea <claudiu.beznea@...on.dev>
Subject: [PATCH 1/2] net: phy: Check phydev->drv before dereferencing it

The macb driver calls mdiobus_unregister() and mdiobus_free() in its remove
function before calling unregister_netdev(). unregister_netdev() calls the
driver-specific struct net_device_ops::ndo_stop function (macb_close()),
and macb_close() calls phylink_disconnect_phy(). This, in turn, will call:

phy_disconnect() ->
  phy_free_interrupt() ->
    phy_disable_interrupts() ->
      phy_config_interrupt()

which dereference phydev->drv, which was already freed by:
mdiobus_unregister() ->
  phy_mdio_device_remove() ->
    device_del() ->
      bus_remove_device() ->
        device_release_driver_internal() ->
          phy_remove()

from macb_close().

Although the sequence in the macb driver is not correct, check phydev->drv      
before dereferencing it in phy_config_interrupt() to avoid scenarios
like the one described.

Fixes: 00db8189d984 ("This patch adds a PHY Abstraction Layer to the Linux Kernel")
Signed-off-by: Claudiu Beznea <claudiu.beznea@...on.dev>
---
 drivers/net/phy/phy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
index a5fa077650e8..dd98a4b3ef81 100644
--- a/drivers/net/phy/phy.c
+++ b/drivers/net/phy/phy.c
@@ -165,7 +165,7 @@ EXPORT_SYMBOL_GPL(phy_get_rate_matching);
 static int phy_config_interrupt(struct phy_device *phydev, bool interrupts)
 {
 	phydev->interrupts = interrupts ? 1 : 0;
-	if (phydev->drv->config_intr)
+	if (phydev->drv && phydev->drv->config_intr)
 		return phydev->drv->config_intr(phydev);
 
 	return 0;
-- 
2.39.2