[PATCH net v2] net: usb: lan78xx: avoid NULL PHY dereference in WoL setup

[Prashant Sengar <prashantsengar25031@gmail.com>]

LAN7801 supports fixed-link configurations without an attached PHY.
However, lan78xx_set_wol() unconditionally passes netdev->phydev
to phy_ethtool_set_wol(), causing a NULL pointer dereference when
a userspace WoL request reaches this path.

Use phylink_expects_phy() to skip PHY WoL configuration for fixed
links, and use phylink_ethtool_set_wol() for configurations that
expect a PHY. This avoids the NULL dereference while keeping PHY
operations within the phylink API.

The issue was reproduced using USB Raw Gadget and dummy_hcd in QEMU.
An ETHTOOL_SWOL ioctl triggered a kernel Oops with the original
driver. With this change, the same request completes successfully.

Fixes: e110bc825897 ("net: usb: lan78xx: Convert to PHYLINK for improved PHY and MAC management")
Signed-off-by: Prashant Sengar <prashantsengar25031@gmail.com>
---
v2:
  - Use phylink_expects_phy() to avoid PHY WoL operations for
    fixed-link configurations.
  - Use phylink_ethtool_set_wol() instead of the direct PHY
    helper, addressing Andrew Lunn's review.
  - Preserve the existing controller WoL configuration order.
v1: https://lore.kernel.org/netdev/20261018151830.643511-1-prashantsengar25031@gmail.com/
 drivers/net/usb/lan78xx.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index 5655941f1478..1702f633d42e 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -1805,7 +1805,9 @@ static int lan78xx_set_wol(struct net_device *netdev,
 	if (ret < 0)
 		goto exit_pm_put;
 
-	ret = phy_ethtool_set_wol(netdev->phydev, wol);
+	if (phylink_expects_phy(dev->phylink))
+		ret = phylink_ethtool_set_wol(dev->phylink, wol);
+
 
 exit_pm_put:
 	usb_autopm_put_interface(dev->intf);
-- 
2.55.0